Effects of asteroid and comet impacts on habitats for ...€¦ · interior of rocks can be an...

Meteoritics amp Planetary Science 40 Nr 12 1901ndash1914 (2005)Abstract available online at httpmeteoriticsorg

1901 copy The Meteoritical Society 2005 Printed in USA

Effects of asteroid and comet impacts on habitats for lithophytic organismsmdashA synthesis

Charles S COCKELL1 Pascal LEE2 Paul BROADY3 Darlene S S LIM2 Gordon R OSINSKI4John PARNELL5 Christian KOEBERL6 Lauri PESONEN7 and Johanna SALMINEN7

1Planetary and Space Sciences Research Institute Open University Milton Keynes MK7 6AA UK2NASA Ames Research Center Moffett Field California 94035ndash1000 USA

3School of Biological Sciences University of Canterbury Private Bag 4800 Christchurch New Zealand4Canadian Space Agency 6767 Route de lrsquoAeroport Saint-Hubert Quebec J3Y 8Y9 Canada

5Department of Geology University of Aberdeen Aberdeen AB24 3UE UK6Department of Geological Sciences University of Vienna Althanstrasse 14 A-1090 Vienna Austria

7Division of Geophysics Department of Physical Sciences University of Helsinki PO Box 64 00014 University of Helsinki FinlandCorresponding author E-mail cscockellopenacuk

(Received 04 April 2005 revision accepted 03 August 2005)

AbstractndashAsteroid and comet impacts can have a profound influence on the habitats available forlithophytic microorganisms Using evidence from the Haughton impact structure Nunavut CanadianHigh Arctic we describe the role of impacts in influencing the nature of the lithophytic ecologicalniche Impact-induced increases in rock porosity and fracturing can result in the formation ofcryptoendolithic habitats In some cases and depending upon the target material an increase in rocktranslucence can yield new habitats for photosynthetic cryptoendoliths Chasmoendolithic habitatsare associated with cracks and cavities connected to the surface of the rock and are commonlyincreased in abundance as a result of impact bulking Chasmoendolithic habitats require less specificgeological conditions than are required for cryptoendolithic habitats and their formation is likely tobe common to most impact events Impact events are unlikely to have an influence on epilithic andhypolithic habitats except in rare cases where for example the formation of impact glasses mightyield new hypolithic habitats We present a synthetic understanding of the influence of asteroid andcomet impacts on the availability and characteristics of rocky habitats for microorganisms

INTRODUCTION

Rocks offer a diversity of habitats to microorganismsand although they might superficially appear to be similareach habitat can experience different microclimaticconditions and each habitat may host different colonistsThus it is of biological importance to distinguish betweenthem

To identify the different habitats in this paper we followthe terminology of Golubic et al (1981) Table 1 and Fig 1summarize the habitats with the names of the organisms thatinhabit them

The interior of rocks has merited particular attention inextreme deserts of the world as a potential habitat formicroorganisms on account of the amelioratedenvironmental conditions that are often found in thesehabitats compared with their surfaces (Friedmann 1980)Cryptoendolithic and chasmoendolithic organisms are not

limited to extreme environments Endolithic attack ofbuildings is a matter of concern in many cities and towns(Sterflinger and Krumbein 1997) Nonetheless inenvironments where the surfaces of rocks are exposed toextremes of temperature UV radiation and desiccation theinterior of rocks can be an important refugium for life

The opportunities that rock interiors afford as an escapefrom environmental extremes has made them the subject ofinterest as possible locations for life on early Earth (Westalland Folk 2003) and more speculatively on the surface ofother planets (Wierzchos et al 2003) The discovery ofPrecambrian endoliths attributed specifically to euendolithicorganisms (Campbell 1982) shows that lithic habitats haveprobably been important throughout the history of life onEarth

The manner in which microorganisms colonize rocks isof profound importance for a number of fields ofmicrobiology and earth sciences as these microbial

1902 C S Cockell et al

communities can influence weathering (Warscheid andKrumbein 1994) and rates of biogeochemical cycling(Johnston and Vestal 1989) Furthermore discrete ecosystemscan become established within rocks allowing for elementalcycling and nutrient gradients which benefit many differentmicroorganisms (Friedmann 1982)

Asteroid and comet impacts generate pressures andtemperatures that can vaporize melt shock metamorphose

andor deform a substantial volume of the pre-impact targetsequence (eg Grieve and Pesonen 1992) This profoundinfluence on target materials can change the availability andcharacteristics of habitats for lithophytic organisms (Cockellet al 2002) As impact events are a universal phenomenonand would have been more frequent on the early Earth thantoday understanding their influence on habitats formicroorganisms is a fundamental objective in microbiology

In this paper we use data gathered at the Haughtonimpact structure Nunavut Canada in combination with datafrom other craters to develop a synthetic understanding of theeffects of impact on habitats for lithophytic organisms

BIOLOGICAL CHARACTERISTICS OF THE FIELD SITE

The Haughton impact structure is located on DevonIsland Nunavut Canadian High Arctic and is centered at75deg22primeN and 89deg41primeW By geophysical criteria the structurehas an apparent diameter of about 24 km (Pohl et al 1988)

Table 1 Habitats for lithophytic organisms and some of the effects of asteroid and comet impacts on their abundance and characteristics (nomenclature after that of Golubic et al 1981)

Name of habitat Description of habitatEffects of impact at Haughton General effects of impacta

Cryptoendolithic Habitat within the interior of the rock

Increase in interconnected pore spaces in shocked gneiss and increase in translucence results in greater habitat availability

Impact-induced fractures and pore space is likely to increase interior space for colonization in many rock types However photosynthetic endoliths require light penetration Impact alteration of rock translucence may change availability of habitat

Chasmoendolithic Habitat in fissures and cracks within rock

Increase in habitats caused by fracturing of rocks General to many rock types characterized in dolomite

Impact-induced fractures and fissures are likely to make an increase in chasmoendolithic habitat a common occurrence in impact structuresb

Euendolithic Habitat formed by active boringpenetration by microorganisms

Euendolithic organisms not studied However habitat (carbonates) form immiscible melts with other target materials

Increase in pore space caused by shock or changes in density of rock and rock chemistry (eg heterogeneous carbonate melts) could plausibly affect the ease with which microorganisms can actively penetrate into rocks

Epilithic Habitat on surface of rocks

No evidence for change in habitat availability

The habitat on the surface of rocks will generally be unaffected by impact However two possible modes of change in suitability for colonization could be 1) changes in weathering rates caused by mineralogical changes eg melting could cause changes in the abundance of surface attachment sites (eg caused by changes in surface roughness) or 2) changes in macronutrient availability might change suitability of rock surfaces for microbial biofilm formation

Hypolithic Habitat on underside of rock


The habitat on the underside of rocks will generally be unaffected by impact A possible instance in which hypolithic habitat availability could be changed would be alterations in the translucence of rocks (for example the formation of impact glasses in desert settings) which would alter suitability of underside of rocks for photosynthetic hypoliths

aHabitat availability can be changed by for example the emplacement of a melt sheet (ejecta blanket) over previously available lithic habitats The impact meltbreccia hills of the Haughton impact structure cover Palaeozoic dolomite which in other regions of Devon Island and the High Arctic provide abundanthypolithic habitat (Cockell and Stokes 2004) However in this paper we focus on the direct effects on rocks caused by shock metamorphism

bCyanobacterial chasmoendoliths have recently been reported from shocked limestones in the Ries impact structure (Cockell et al 2004)

Fig 1 Lithic habitats (see Table 1 for descriptions)

Effects of asteroid and comet impacts on habitats for lithophytic organisms 1903

although recent detailed structural mapping indicates that avalue of 23 km is more accurate (Osinski and Spray 2005)The structure was formed in a target sequence dominated by athick series (sim1880 m) of Lower Paleozoic marinesedimentary rocks comprised of mostly carbonates (dolomiteand limestone) overlying a basement of Precambrian granitesand gneisses (Thorsteinsson and Mayr 1987 Osinski et al2005a) During the impact event the crater was filled with animpact melt breccia deposit a rubble-like mixture of targetrocks dominated by carbonates (Figs 2 and 3a) (Grieve 1988Osinski and Spray 2001 Osinski et al 2005b) which has amaximum preserved thickness of sim125 m and covers an areasim60 km2 (Scott and Hajnal 1988) The original dimensions ofthe impact melt breccia deposit are estimated to be greaterthan 200 m in thickness and sim12 km in diameter (Osinski et al2005b) This unit still covers most of the crater interior anotable exception being a sim8 km2 area in the west-centralregion of the structure which is comprised of paleolacustrinedeposits laid down within a lake (the Haughton Formation)which formed some time after the impact event (Frisch andThorsteinsson 1978 Roberston and Sweeney 1983 Hickeyet al 1988 Whitlock and Dawson 1990 Osinski and Lee2005) although it was certainly not formed immediately post-impact (see discussion in Osinski and Lee [2005]) In theeastern part of the crater the impact melt breccia deposits are

divided into a series of discrete outcrops separated from themain deposits in the central part of the crater by a system ofbroad (up to sim1 km wide) alluvial terraces associated withmeanders of the Haughton River (Fig 2)

Haughton crater and the region around it are situated intypical polar desert In High Arctic polar deserts vegetationcover is less than 5 and fauna depauperate compared to LowArctic ecosystems (Babb and Bliss 1974 Bliss et al 1984)This is the case for most of Devon Island apart from localizedregions such as the coastal Truelove Lowlands in whichbiological productivity is substantially greater (Svoboda1977) Similar to other sites on Devon Island (eg Walkerand Peters 1977 Bliss et al 1994) the soils of the Haughtonregion are primarily dolomitic and are nutrient poor The lowproductivity of the soils is exacerbated by the climaticconditions Devon Island lies within region IVa of Maxwellrsquos(1981) climatic regions of the Canadian Arctic Archipelagoand experiences a short growing season caused by short coolsummers

Ecologically the crater itself can be divided into severaldiscrete regions (Figs 2 and 3) The impact melt breccia hillshave low vegetation cover with generally less than 03 withlocalized increases to gt25 in meltwater run-off channels(Fig 3a) (Cockell et al 2001) Higher vegetation covers arefound on the alluvial terraces at the edges of the Haughton

Fig 2 A simplified map of the Haughton impact structure showing the main areas of ecological distinctiveness


River where covers can exceed 10 of the area in places butgenerally they are closer to 2 (Fig 3b) The paleolacustrinesediments of the Haughton Formation support a much richerecology with vegetation cover in some areas greater than 80(Fig 3c) This impact-induced polar oasis is sustained by therich organic content of the sediments and possibly enhancedby their unconsolidated nature and by water draining into thecrater hydrologic depression (Cockell and Lee 2002) TheLowell Oasis supports arctic fox hare and musk ox duringthe summer months and it is richly covered in lemmingburrows Within the crater are numerous ponds and lakeswhose limnological characteristics have been investigated(Lim and Douglas 2003) They are mainly alkalinephosphorus-limited ultra-oligotrophic (nutrient-poor)environments

The lithic habitats discussed in this paper are localized tothe impact melt breccia hills and the regions of dolomiticpolar desert between them (Figs 2 and 4) Outcrops within thepaleolacustrine sediments are very sparse this region of thecrater is dominated by large areas of vegetation-covered soils

CRYPTOENDOLITHIC HABITATS

Cryptoendolithic organisms live within the interstices ofrocks invading the pore spaces to reach the interior of thematerial An increase in porosity caused by impact bulkingand fracturing has been observed in many shocked rocklithologies in comparison to their unshocked forms (Table 2)However a mere increase in porosity is not sufficient forcreating cryptoendolithic habitats The pore space must beinterconnected in order to allow microorganisms to access theinterior of the rock from the surface and allow them to spreadwithin the rock matrix itself (eg Saiz-Jimenez et al 1990)As impact bulking creates fractures and deformation featureswithin target rocks the increase in porosity is oftenaccompanied by an increase in fracturing which allowsmicroorganisms to move within the rock matrix either bygrowth along surfaces or by water transport (Cockell et al2002)

At Haughton we have observed an increase in porosityin impact-shocked gneiss (Cockell et al 2002) The density

Fig 3 Field photographs showing the different types of ecological regions within the Haughton impact structure a) Impact melt breccias All-terrain vehicles (ATVs) are shown in the foreground for scale b) An image from a helicopter looking south down the Haughton River valleyshowing the alluvial terraces c) Paleolacustrine sediments of the Haughton Formation are richly vegetated compared to other parts of the craterd) Target rocks in the interior of the central uplift at Haughton are highly fractured and brecciated ATVs are shown in the foreground for scale


Fig 4 Lithophytic habitats in the Haughton impact structure a) Melt-rock mound (sim100 m in diameter) b) Cryptoendolithic colonization ofshocked gneiss exposed on melt rocks evident as a layer of green in the rock (image is 10 cm across) c) Heavily impact-fractured dolomiteblock at 75deg2440primeN 89deg4989primeW (circumference of block is 153 m) d) Cyanobacterial colonization of impact fractures within the dolomiteblock e) Pond formed adjacent to melt-rock outcrop at 75deg2453primeN 89deg4977primeW Note the black ring around the pond that is caused bycyanobacterial epilithic colonization of rock surfaces (pond is sim8 m in width) f) Colonization of the surface of impact-shocked gneiss bycyanobacteria (black patches on rock) g) Typical sorted ground in dolomite on Devon Island at 75deg2519primeN 84deg4814primeW (image is sim2 macross) h) Hypolithic colonization of sorted dolomite rocks evident as a green layer under the rock


Table 2 Summary of published density and porosity data of impact structures Impact rocks Target rocks

Property Melt Suevite Breccia Fractured Unfractured

Horizontal profilesBosumtwia D sim105 km age sim107 Ma (Ghana)rrrc ndash 147 ndash ndash 135Density ndash 2040 ndash ndash 2510Porosity ndash 256 ndash ndash 83

Ilyinetsb D sim8 km age sim378 Ma (Ukraine)rrrc 045 043 044 044 115Density 2349 2113 2289 2462 2650Porosity 57 154 111 52 11

Jpermilnisjpermilrvic D sim15 km age sim700 Ma (Russia)rrrc 04 03 04 03 169Density 2569 2540 2536 2484 2775Porosity 28 72 50 71 05

Karikkoselkpermild D sim24 km age sim19 Ma (Finland)rrrc ndash ndash boulder 056 221Density ndash ndash 2490 2637 2653Porosity ndash ndash 72 15 13

Popigaie D sim100 km age sim357 Ma (Russia)rrrc 072 071 ndash ndash 074Density 2522 1890 ndash ndash 2775Porosity 50 86 ndash ndash 04

Vertical profilesKpermilrdlaf D sim4 km age sim455 Ma drill core (Estonia)rrrc ndash 026 ndash 1 ndashDensity ndash 2390 ndash 2680 ndashPorosity ndash 93 ndash 135 ndash

Lappajpermilrvig D sim23 km age sim733 Ma drill core (Finland)rrrc 0011 0012 ndash ndash ndashDensity 2596 2297 ndash ndash ndashPorosity 14 167 ndash ndash ndash

Suvasvesi Nh D sim4 km age sim240 Ma drill core (Finland)rrrc 012 013 ndash ndash 107j

Density 2369 2427 ndash ndash 2804j

Porosity 148 97 ndash ndash 06j

Spermilpermilksjpermilrvii D sim6 km age sim600 Ma drill core (Finland)rrrc ndash ndash ndash ndash ndashDensity ndash 2280 2170 2343 2597Porosity ndash 151 199 130 66

Mean N = 9 Density 2481 2247 2371 2521 2685Porosity 59 135 108 56 27Trend Density increases and porosity decreases

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯rarrrrrc is the normalized distance where rr is the distance from the structurersquos center and rc is radius of the structure D is diameter of the structure density

(kgmminus3) is generally bulk density in laboratory conditions porosity () is measured using Archimedean principle (eg Kivekpermils 1993) jLateral samplingon the surface

aPlado et al 2000 bPesonen et al 2004 cSalminen 2004 dPesonen et al 1999 eSalminen unpublished data fPlado et al 1996 gKukkonen et al 1992hWerner et al 2002 iKivekpermils 1993 Note that the porosity of impact melt breccias from Haughton crater measured using the Archimedean principle(Pesonen this work see Pesonen et al 2004 for discussion) was determined as 314 plusmn 24 (mean of 6 samples) the porosity of impact-shocked gneiss(sim20ndash40 GPa shock pressures) was measured as 183 plusmn 23 and the porosity of unshocked rocks was measured as 93 plusmn 12 All samples were obtainedat melt rock hill adjacent to 75deg2453primeN 89deg4977primeW


and porosity of shocked rocks (shocked to gt20 GPa) is on theorder of 1 times 103 kgmminus3 and 183 respectively (Table 2) Thelow-shocked or unshocked rocks have a more typical densityand porosity of gt25 times 103 kgmminus3 and 93 respectively

The volatilization of opaque minerals and the formationof fractures within the rock matrix increases the translucenceof the shocked gneiss Penetration of light at 680 nm thechlorophyll a absorption maximum is increased by about anorder of magnitude (Cockell et al 2002) compared tounshocked rocks If the minimum light for photosynthesis istaken to be 20 nmolm2s (Raven et al 2000) then thiscorresponds to a depth of approximately 36 mm in theshocked material but about 1 mm in the low-shockedmaterial This latter depth prevents the cyanobacteria fromcolonizing the interior of the unshocked rock except withinthe weathering crust where rare chasmoendolithiccolonization is observed The porosity of the unshocked rocksis also insufficient for cyanobacterial cryptoendolithiccolonization In the shocked material coherent bands ofcryptoendolithic colonization at depths typically sim1ndash5 mmcan be found (Figs 4a and 4b)

The interconnected fractures within the shocked materialprovide a habitat suitable for a wide diversity of non-photosynthetic heterotrophic (organic-using) microorganisms(Fike et al 2003) These microorganisms are similar to thosefound in soils and ices elsewhere in polar regions and theyprobably leach into the rock from the soils in seasonal snowmelt or rain and subsequently form biofilms within the rockmatrix

The interior of the shocked rocks provides protectionfrom environmental stress(es) Within the rock temperaturesduring the summer months are often higher than the airtemperature sometimes by up to 10 degC (Cockell et al 2003a)After short rain falls moisture becomes trapped within thepore spaces of the shocked rocks providing water for theorganisms after the surface has dried in the wind The interiorof the rocks also protects against UV radiation damage(Cockell et al 2002)

The cryptoendolithic photosynthetic organisms foundwithin the Haughton gneiss demonstrate impact-inducedformation of cryptoendolithic habitats but more specificallythey demonstrate how shock metamorphism can yieldcryptoendolithic habitats in non-sedimentary lithologieswhich are otherwise unusual Endolithic colonization of non-sedimentary rocks has been reported in weathering crusts andcracks in granite manifested as chasmoendolithiccolonization (eg Friedmann 1977 De los Rios et al 2005)However the best characterized photosyntheticcryptoendolithic habitats are those associated with sandstonesand limestones (eg Friedmann 1982 Saiz-Jimenez et al1990 Bell 1993 Wessels and Bcedildel 1995) Sedimentaryrocks such as these are sufficiently translucent and porous forcryptoendolithic colonization

The process of shock metamorphism is thus not merely

about increasing the porosity and translucence of non-sedimentary rocks for photosynthetic cryptoendolithiccolonists but it involves creating conditions for colonizationin non-sedimentary rocks which would not have beenpreviously available

Impact events generate new lithologies (eg impactbreccias and melt rocks) that can be more porous than the pre-impact target rocks and at least have sufficient porosity forcolonization For example surficial or fallout suevites at theRies impact structure Germany typically have porosities ofsim5ndash15 vol (Osinski et al 2004) We have shown how thebreccias and melt rocks of the Haughton structure aresufficiently porous to sustain heterotrophic microbialpopulations (Fike et al 2003) Thus the interior of melt rockscan host diverse assemblages or communities of non-photosynthetic microorganisms Although these organisms donot form the highly structured layered communities typicallyassociated with photosynthetic cryptoendolithiccommunities they are nevertheless lithophytic organismsassociated with high porosities generated in impact-alteredtarget materials

CHASMOENDOLITHIC HABITATS

Chasmoendolithic organisms depend upon macroscopiccracks and fissures in rocks as a habitat The most widelycharacterized chasmoendoliths are cyanobacterial colonists(Bcedildel and Wessels 1991 Broady 1979 1981a)Chasmoendolithic habitats have particular importance inpolar regions for the same reasons as those described forcryptoendoliths (Broady 1981a) The interior of the cracksand fissures provides escape from desiccation rapidtemperature variations and UV radiation Unlikecryptoendolithic habitats chasmoendolithic habitats can beformed in potentially any substrate Provided that thesubstrate is not toxic then any macroscopic cracks canprovide surfaces for growth Unlike cryptoendolithic habitatsphotosynthetic organisms do not require that the substrate istranslucent because light penetrates from the surface directlyinto the cracks in the substrate

In the Haughton structure cyanobacterialchasmoendolithic communities are evident in impact-shattered dolomites (Cockell and Lim 2005) In particularlarge regions of the central uplift are highly fractured faultedand brecciated (Fig 3d) as well as several large ejecta blocks(Figs 4c and 4d) Coccoid cyanobacterial colonists withGloeocapsa-like and Chroococcidiopsis-like morphologyhave invaded the substrate along fracture planes Similarcolonization is not observed in unshocked dolomitic erraticsfound outside the crater

Shattered limestones from the Ries crater in Germany arealso found to harbor cyanobacterial chasmoendolithiccommunities (Cockell et al 2004) Similarly to Haughton theorganisms invade the fracture planes


Impact-induced fracturing is common to all impactevents and so the simplest statement that can be madeconcerning the effects of impact on the chasmoendolithichabitat is that shock metamorphism can increase theabundance of habitats These habitats may form in thesubsurface as well as the surface but at the surface wherephotosynthetically active radiation is available impact-induced chasmoendolithic habitats will then provide a habitatfor photosynthetic pioneers These habitats will beparticularly important in the fractured and faulted centraluplifts and uplift rings of complex impact structures

AN INCREASE IN CHASMOENDOLITHIC AND CRYPTOENDOLITHIC HABITATS IS LIKELY

TO BE A COMMON EFFECT OF IMPACT

The most microbiologically important effect of impact isbulkingmdashincreasing the porosity of rocks and the abundanceof interconnected fractures As lithophytic microorganismsrequire surfaces on which to grow an increase in porosity andfracturing can increase the availability of surfaces formicrobial growth However as organisms might be nutrient-limited it is not necessarily the case that an increase insurface area for growth will be correlated to an increase inbiomass Thus it is important to understand that the effect ofimpact is to increase the potential for growth specificallywith respect to surface area for biofilm formation

It is well-known that densities of impact rocks can beup to 30 lower than in unshocked target rocks due toimpact-increased porosity and fracturing (Pesonen et al1999 Henkel 1992 Pilkington and Grieve 1992 Pladoet al 1996) In some cases natural shock-induced fracturinghas been accurately replicated in laboratory shockexperiments providing a quantitative understanding of theprocess such as for example in the case of shocked basaltsfrom the Lonar crater India (Kieffer et al 1976a) Thesecollected observations suggest that chasmoendolithic andcryptoendolithic habitat formation are common to impactcratering and common to many different lithologies

Several craters either directly or indirectly demonstratethat shock metamorphism causes an increase in the potentialaccessibility of target lithologies to a microbiota Calculatedshock determinations based on mineralogy are available forthe Charlevoix impact structure Quebec (D = 54 km agesim342 Ma) (Grieve et al 1990) This example (Fig 5a)illustrates the radial (in this case horizontally) decay ofshock from the centre of the structure (close to the point ofimpact) The observed rate of recorded shock pressureattenuation is almost exponential from about 20 GPa nearthe center to about 4 GPa at 10 km distance from the centerand up to the rim Unfortunately no porosity determinationsare available

Figure 5b shows the decay of fracture density as afunction of distance for the Elgygytgyn structure Russia (D =

18 km age = 35 Ma) (Gurov and Gurova 1983) We note thatthe fracture density decreases exponentially away from theimpact centre The effectiveness of shock metamorphism atopening pore space and increasing the abundance of fracturesis reflected in the data of electrical conductivity in and aroundthe Siljan impact structure Sweden where conductivitydiminishes outwards from the centre of the structure (Fig 5d)(Henkel 1992) The increasing electrical conductivity into thecentre of Siljan is proposed to be caused by the presence ofsaline fluids in pores and fractures an indirect demonstrationof impact-induced fracturing

Table 2 summarizes the porosity data of nine impactstructures The rocks have been divided into two categoriesimpactites (divided into melts suevites and breccias) andtarget rocks (divided into fractured and unfractured) Theseunits roughly correspond to the increasing distance eitherdownward (drill core data) or radially away (lateral sampling)from the point of impact However the distances (rrrc) are tobe viewed only as rough measures of the original radialdistance since the structures are different in their diameterage erosional level and tectonic modification Neverthelesswe note that generally the porosity decreases when movingaway from impactites to fractured and to unfractured targetrocks For example in the case of the Jpermilnisjpermilrvi impactstructure (Fig 5c) (Salminen 2004) the porosity has a trend todecrease (from approximately 10) in impactites to theunfractured target rocks (approximately 05) (Fig 5c)consistent with decreasing shock pressure

The higher porosity observed in the subsurface of impactstructures compared to their exteriors (Table 2) shows thatimpact events could potentially render the subsurface moreamenable to colonization by microbiota as well as theirsurface habitats However the biomass of subsurface biotaappears to be correlated to availability of redox couplesrather than availability of pore or fracture space (Wellsburyet al 1997 DrsquoHondt et al 2004 Parkes et al 2005) and soalthough impact-induced fracturing might increase the easewith which biota can colonize rocks it is not necessarily thecase that fracturing in the deep subsurface would providesignificant advantages to a nutrient-limited biota On theother hand the fracturing of rock could potentially enhancethe supply of electron donors and acceptors examples beingthe fracturing of basalts to yield hydrogen wherebyferromagnesium silicates reduce water a process which hasbeen demonstrated using crushed basalt in the laboratoryalbeit at quite narrow pH ranges (Anderson et al 1998) or thefracturing of iron-rich rocks to yield new sources of reducedor oxidized iron for iron-utilizing microorganisms Howeverthese transient availabilities of energy supplies may beirrelevant in regions sterilized by the thermal pulse from theimpact or they may be too short-lived to be useful overgeological time scales (Anderson et al 1998)

Impact events can alter the oxidation state of metalsgeochemical studies show that the conditions of impact may


be reducing evidenced by low ferric iron to ferrous iron ratiosin tektites (Koeberl 2004) This process could potentially alterthe bioavailability of redox couples and nutrients in post-impact lithophytic habitats both at the surface and in thesubsurface

Other subtleties must be understood when formulating asynthetic understanding of the role of impact in influencinglithophytic habitats First lithology does play a role in thenature of the post-impact lithophytic habitat In the case ofsedimentary lithologies with high porosities some of theenergy delivered in impact causes pore collapse thusreducing porosity Kieffer and co-workers showed that in theCoconino sandstones at Meteor crater Arizona the porosityof the material was reduced from approximately 20 (Kieffer1975) to less than 5 (Kieffer 1971) following low shockpressures Thus in some cases impact will reduce pore spaceavailable for endolithic colonization in rocks that were very

porous prior to impact The reduction in porosity was causedby the re-orientation of the grains into a more closely packedconfiguration At high shock pressures (although stilllt25 GPa) the grains become highly fractured and deformedeventually plastically flowing around each other (Kieffer1971) Hot material is ldquojettedrdquo into pore spaces (Kieffer et al1976b) The density of the shocked Coconino samples wasnot reduced to the intrinsic density of the material Theremaining porosity within the shocked material wasaccounted for by the space between the re-oriented grains orthe fractured rocks In the case of heavily fractured rocks thehabitat may be partly held together by the interlockingfragments of shocked rock rather than the arrangement ofseparate grains We would predict that in some high porositylithologies impact shock will reduce bulk porosity andimpede colonization However concomitantly by fracturingthe rock and its component grains thus increasing surface

Fig 5 Some physical properties of impact structures as a function of the horizontal distance from the structurersquos center point (rrrc is thenormalized distance where rr is the distance from the structurersquos center and rc is radius of the structure) a) Calculated shock pressure inCharlevoix structure (after Grieve et al 1990) b) density of fracturing in Elgygytgyn structure (after Gurov and Gurova 1983) c) porosity ofthe Jpermilnisjpermilrvi structure (Salminen 2004) d) electrical conductivity of the Siljan structure (modified after Henkel 1992)


area and potentially the interconnectedness of the interiorrock space the effects of the reduction of bulk porosity couldbe partly mitigated

Second intense shock lithification can cause melting ofthe material and the formation of glass Glass formation hasbeen observed in many shocked lithologies for example inthe basalts and sandstones discussed earlier (Kieffer 1976a1976b) In these two cases glass formation was observed atshock pressures gt50 GPa Glass within the Coconinosandstone was found to form continuous ribbons aroundquartz grains and it filled the intergrain spaces Althoughmany of these glasses were found to have a microscopicstructure that was irregular patches of homogeneous glassformation in the interstices of the rock could impede potentialcolonists

Although there are complexities to the impact-inducedformation of lithophytic habitats that are determined by shockpressures lithology and nutrient availability it is evident thatgeologic changes such as shock metamorphism andfracturing result in some changes in biological potential thatare common to all impact events the most important being anincrease in fractures for potential chasmoendolithic andcryptoendolithic colonists

EUENDOLITHIC HABITATS

We have not undertaken a study of euendolithicorganisms within the crater but we have studied theeuendolithic habitat The most common habitat foreuendoliths which actively bore into rock is in carbonatelithologies (Hoppert et al 2004) The most investigated genusof euendolithic cyanobacteria is Hyella Corals provide asource of biogenic carbonates and have been a previous focusof study on euendolithic organisms (Le Campion-Alsumard etal 1995 Tribollet and Payri 2001) Carbonates are readilydissolved by organic acids produced by euendoliths allowingthem to bore into the substrate (Fig 1) Similarly to thecrypto- and chasmoendolithic habitat the euendolithic habitatprovides protection from environmental extremes

Carbonates are present in the target rocks ofapproximately one-third of the worldrsquos known impactstructures Despite the many uncertainties regarding theresponse of carbonates to impact it is commonly acceptedthat these lithologies decompose after pressure release due tohigh residual temperatures (eg Agrinier et al 2001) Thusone effect of impact on the euendolithic habitat is simply tovaporize it However recent studies suggest that the dominantprocess is melting and not decomposition (eg Graup 1999Jones et al 2000 Osinski and Spray 2001) a view supportedby the phase relations of CaCO3 (Ivanov and Deutsch 2002)At Haughton the carbonate melts are mixed with other meltphases including sulfate minerals and impact glasses(Osinski and Spray 2001 2003 Osinski et al 2005b) Themelt phases are mixed on micrometer to millimeter scales

and the mixing of the carbonates with other target lithologiesresults in a physically and chemically heterogeneoussubstrate These substrates would be expected to be moredifficult to bore than unaltered carbonates as euendolithicbore holes are more likely to encounter other melt phases orclasts of target materials that do not readily lend themselves todissolution by organic acids such as sulfates in the case of theHaughton structure

Thus we would expect the formation of heterogeneousmelts and inclusion of unmelted clasts to impede penetrationof euendoliths into impact melt brecciasrocks depending onthe degree of melting and the exact composition of the targetlithologies Conversely however increases in porosity byimpact bulking might be predicted to render some carbonaterocks more amenable to euendolithic colonization and tooffer a greater surface area for initial attachment andcolonization in analogy to post-impact chasmoendolithiccolonization The carbonate lithologies in the central uplift atHaughton are highly fractured and brecciated (Fig 3)

In addition to carbonate lithologies euendolithic boringshave been found in basaltic glasses (eg Thorseth et al 1992Fisk et al 1998) The organisms within these glasses arepreferentially found at the margins of glasses where access tothe substrate and possibly nutrient supplies are availableImpact melt glasses formed at high shock pressures andemplaced within the target lithology offer similar potentialmicrohabitats for euendolithic glass-boring colonists

EPILITHIC HABITATS

The surface of rocks which provide a stable surface onwhich biofilms can develop provide a habitat for anextraordinary diversity of microorganisms Some of theserock surface biofilms particularly in the worldrsquos hot desertsform distinctive desert ldquovarnishesrdquo and crusts (eg Kurtz andNetoff 2001 Perry et al 2003) At Haughton cryptogamiccrusts are abundant particularly in areas where seasonalmeltwater water is channeled These crusts are primarilyformed from diverse cyanobacterial assemblages includingNostoc spp Gloeocapsa spp and filamentous cyanobacteriasuch as Phormidium and Scytonema and they can alsocontain lichens and mosses in more luxuriant standsCyanobacterial epiliths have been observed on and withingypsum outcrops in Haughton (Parnell et al 2004)Cryptogamic epilithic crusts and cyanobacterial mats arewidespread in the arctic and have been reported from anumber of locations (eg Gold and Bliss 1995 Quesada et al1999 Dickson 2000) We have not observed any effect ofimpact metamorphism on epilithic colonization Aroundtransient meltwater streams and in topographic lows impactaltered clasts such as gneiss provide surfaces for epilithiccolonization similarly to nearby locations outside the crateron Devon Island (Figs 4e and 4f) We have observed lowervegetation covers on the top of the impact melt breccia hills at


Haughton compared to the alluvial terraces at the edges of theHaughton River and compared to other locations that havebeen studied on Devon Island (Cockell et al 2001) but weattributed this to desiccation experienced on the top of thehigh exposed hills rather than to impact alteration of therocks themselves

As epilithic organisms will colonize any surface whereadequate nutrients and water are available there is no obviousmechanism by which impact metamorphism would directlyalter the epilithic habitat except by changing the chemistry ofthe rocks and thus the potential source of nutrients or redoxcouples for surface-attached organisms As discussed earlierthe reduction of metals during the impact process (egKoeberl 2004) is one such mechanism by which potentialsurface chemolithotrophic redox couples could be influenced

The epilithic habitat might well be impoverishedimmediately after impact however when volatilization ofbiologically important nutrients such as phosphorus andnitrogen compounds is likely to have occurred Since themajor biologically important nutrients volatilize attemperatures well below those associated with region affectedby impact shock heating (Cockell et al 2003b) then thesurfaces of rocks are likely be rendered nutrient poorFollowing impact nitrogen fixation phosphorus input fromrain and animals and input of other compounds and traceelements are likely to reduce the chemical differences betweenthe epilithic habitat inside the crater compared to outside

HYPOLITHIC HABITATS

The underside of rocks provides a surface for biofilms ofboth photosynthetic and non-photosynthetic organisms (egSmith et al 2000) In the case of photosynthetic organismsthey have the requirement for light as a source of energy andtherefore hypolithic colonization usually requires that therock is translucent For this reason most hypoliths to datehave been reported under quartz-dominated lithologies (Vogel1955 Cameron and Blank 1965 Broady 1981b Schlesingeret al 2003) which can have sufficient translucence for lightto penetrate directly through the rock to the microbiotaunderneath (Berner and Evenari 1978)

We have not observed any influence of impactmetamorphism on hypolithic colonization at HaughtonShocked clasts exposed on the surface of the Haughton melthills are colonized on their underside by cyanobacterialassemblages similarly to dolomitic rocks outside the craterThese hypoliths are dominated by Gloeocapsa (cf atrataKcediltzing) Gloeocapsa (cf punctata Npermilgeli) Gloeocapsa (cfkuetzingiana Npermilgeli) Aphanothece and Aphanocapsa-likecells and Chroococcidiopsis-like cells (Cockell et al 2002Cockell and Stokes 2004) Various filamentous forms havebeen observed primarily Oscillatoriales similar toLeptolyngbya and Scytonema Unicellular algal chlorophyteswere observed

Hypolithic colonization is widespread in the polar desertof the Canadian High Arctic (Figs 4g and 4h) Wehypothesize that this is caused by cyclical freeze-thaw thatresults in openings around the edges of opaque stones intowhich light can penetrate rather than the translucence of therocks themselves (Cockell and Stokes 2004) In some areasover 90 of rocks are colonized on their underside Thusalthough the translucence of the shocked gneiss is greater thanthat of low or unshocked gneiss hypolithic colonization ofthese rocks is not related to impact metamorphism Indeedthe shocked gneiss is still insufficiently translucent to allowadequate light to penetrate for photosynthesis even under athickness of 1 cm

An instance in which impact metamorphism mightincrease the abundance of hypolithic habitats is when impactglasses are formed in sandy deserts or in sandstonelithologies The colonization of the underside of impact-generated translucent melt-rocks and glasses would presentan example of impact-enhanced hypolithic colonization Itwas noted in the field in an expedition to the Libyan DesertGlass (LDG) strewn field in southwest Egypt (see Koeberlet al 2003 for a first report) that in many cases larger LDGsamples (10 cm and above) which had been in situ in the sandfor a long time (smaller pieces are easily transported by windduring sandstorms) are corroded on their underside In thesecases there was often a thin soil layer attached to the roughunderside of the glass and in many cases green crusts ofphototrophic communities were observed

Conversely impact metamorphism of quartz could evenrender a pre-impact hypolithic habitat (and a quartzcryptoendolithic habitat) less suitable for microbialcolonization if the quartz becomes opaque ldquoToastedrdquo quartzhas been reported to be more opaque than unshockedmaterial This was primarily attributed to the presence of fluidinclusions along planar deformation features (Whiteheadet al 2002) Kieffer et al (1976b) describe the formation ofamorphous ldquofrothrdquo within shocked Coconino sandstones nearhigh-pressure phase regions which they attribute to theviolent separation of vaporized water and silica The highporosity vesicular material causes an increase in lightscattering and thus opacity They have also observed opaqueglasses that surround grains in highly shocked material Thereduction of light penetration through ldquofrothrdquo ldquotoastedrdquo andglassy materials illustrates how impact metamorphism canalter lithophytic habitats in ways that specifically influencepotential colonization by photosynthetic microorganisms

SUMMARY AND CONCLUSIONS

Asteroid and comet impacts cause profound changes totarget rocks which can influence the availability of habitatsfor microorganisms

For epilithic and hypolithic organisms these effects aregenerally not important because they grow on the outside


surfaces of rocks where rock porosity is not a factor ingrowth Except where shock metamorphism alters thetranslucence of rock thus altering the habitat forphotosynthetic hypolithic colonists or where the chemistry ofthe rock is sufficiently altered to influence surfacecolonization hypolithic and epilithic habitats are largelyunaltered by impact Of course melt rocks and ejecta blanketsmight well cover pre-existing lithophytic habitats thusrendering them unsuitable for colonization for example byphotosynthetic organisms but here we are concerned with thedirect effects on the target lithology

The availability of chasmoendolithic habitats can beincreased by the process of shock-induced fracturing andbulking of target rocks which increases the number ofmacroscopic cracks that are accessible from the surface of therock by pioneer organisms As macroscopic cracks do notrequire any special geological attributes of the rock (egcomposition density porosity) impact-inducedchasmoendolithic habitat formation is probably the mostcommon effect of impact on the availability of habitats forlithophytic organisms

Unlike chasmoendolithic colonization the requirementfor interconnected pore spaces for access to the subsurfaceand subsequent spread of biofilms within the rock interiorimposes more specific geological requirements for theformation of cryptoendolithic habitats Photosyntheticcryptoendoliths not only require interior interconnected porespace but also sufficient translucence for light to penetrateinto the rock We have shown how impact-altered gneiss inthe Haughton structure becomes more translucent as a resultof shock metamorphism This process is not necessarilycommon The ldquotoastingrdquo of some target materials may evenrender them more opaque The requirement for both anincrease in interconnected pore spaces and translucencemakes the impact-formation of cryptoendolithic habitats forphotosynthetic organisms in non-sedimentary lithologies aparticularly remarkable and perhaps unusual effect of impacton the habitat for lithophytic organisms

In summary this work has revealed the effects of asteroidand comet impacts on the habitat for lithophytic organismsAn investigation of other impact craters will refine ourunderstanding of these processes and the variations in theirmanifestation This synthesis suggests that impact crateringmust be viewed as a truly biologic process as well as ageologic one (Melosh 1989)

Editorial HandlingmdashDr Scott Sandford

REFERENCES

Agrinier P Deutsch A Schpermilrer U and Martinez I 2001 Fast back-reactions of shock-released CO2 from carbonates Anexperimental approach Geochimica et Cosmochimica Acta 652615ndash2632

Anderson R T Chapelle F H and Lovley D R 1998 Evidence

against hydrogen-based ecosystems in basalt aquifers Science281976ndash977

Babb T A and Bliss L C 1974 Susceptibility to environmentalimpact in the Queen Elizabeth Islands Arctic 27234ndash237

Bell R A 1993 Cryptoendolithic algae of hot semiarid lands anddeserts Journal of Phycology 29133ndash139

Berner T and Evenari M 1978 The influence of temperature andlight penetration on the abundance of the hypolithic algae in theNegev Desert of Israel Oecologia 33255ndash260

Bliss L C Svoboda J and Bliss D I 1984 Polar deserts their plantproduction in the Canadian high arctic Holoarctic Ecology 7324ndash344

Bliss L C Henry G H R Svoboda J and Bliss D I 1994 Patternsof plant distribution within two polar desert landscapes Arcticand Alpine Research 2646ndash55

Broady P A 1979 The terrestrial algae of Signy Island SouthOrkney Islands British Antarctic Survey Science Reports 981ndash117

Broady P A 1981a The ecology of chasmolithic algae at coastallocations of Antarctica Phycologia 20259ndash272

Broady P A 1981b The ecology of sublithic terrestrial algae at theVestfold Hills Antarctica British Phycology Journal 16231ndash240

Bcedildel B and Wessels D C J 1991 Rock inhabiting blue-greenalgaecyanobacteria from hot arid regions Algological Studies64385ndash398

Cameron R E and Blank G B 1965 Soil studiesmdashMicroflora ofdesert regions VIII Distribution and abundance of desertmicroflora Space Programs Summary 4193ndash202

Campbell S E 1982 Precambrian endoliths discovered Nature 299429ndash431

Cockell C S and Lee P 2002 The biology of impact cratersmdashAreview Biological Reviews 77279ndash310

Cockell C S and Lim D S S 2005 Impact craters water andmicrobial life In Water and life on Mars edited by Tokano THeidelberg Springer-Verlag pp 261ndash275

Cockell C S and Stokes M D 2004 Widespread colonization bypolar hypoliths Nature 431414

Cockell C S McKay C P and Omelon C 2003a Polar endolithsmdashAn anticorrelation of climatic extremes and microbialbiodiversity International Journal of Astrobiology 1305ndash310

Cockell C S Osinski G R and Lee P 2003b The impact crater asa habitat Effects of impact processing of target materialsAstrobiology 3181ndash191

Cockell C S Poumlsges G and Broady P 2004 Chasmoendolithiccolonization of impact-shattered rocksmdashA geologically non-specific habitat for microorganisms in the post-impactenvironment (abstract) International Journal of Astrobiology 371

Cockell C S Lee P C Schuerger A C Hidalgo L Jones J A andStokes M D 2001 Microbiology and vegetation of micro-oasesand polar desert Haughton impact crater Devon Island NunavutCanada Arctic Antarctic and Alpine Research 33306ndash318

Cockell C S Lee P Osinski G Horneck H and Broady P 2002Impact-induced microbial endolithic habitats Meteoritics ampPlanetary Science 371287ndash1298

DrsquoHondt S Joslashrgensen B B Miller D J Batzke A Blake R CraggB A Cypionka H Dickens G R Ferdelman T Hinrichs KHolm N G Mitterer R Spivack A Wang G Bekins BEngelen B Ford K Gettemy G Rutherford S D Sass HSkilbeck C G Aiello I W Guegraverin G House C H Inagaki FMeister P Naehr T Niitsuma S Parkes R J Schippers ASmith D C Teske A Wiegel J Padilla C N and AcostaJ L S Distributions of microbial activities in deep subseafloorsediments Science 3062216ndash2221


De los Rios A Sancho L G Grube M Wierzchos J and Ascaso C2005 Endolithic growth of two Lecidea lichens in granite fromcontinental Antarctica detected by molecular and microscopytechniques New Phytologist 165181ndash189

Dickson L G 2000 Constraints to nitrogen fixation by cryptogamiccrusts in a polar desert ecosystem Devon Island NWT CanadaArctic Antarctic and Alpine Research 3240ndash45

Fike D A Cockell C S Pearce D and Lee P 2003 Heterotrophicmicrobial colonization of the interior of impact-shocked rocksfrom Haughton impact structure Devon Island NunavutCanadian High Arctic International Journal of Astrobiology 1311ndash323

Fisk M R Giovannoni S J and Thorseth I H 1998 Alteration ofoceanic volcanic glass Textural evidence of microbial activityScience 281978ndash979

Friedmann E I 1977 Microorganisms in antarctic desert rocks fromdry valleys and Dufek Massif Antarctic Journal of the UnitedStates 1226ndash30

Friedmann E I 1980 Endolithic microbial life in hot and cold desertsOrigins of Life and Evolution of the Biosphere 10223ndash235

Friedmann E I 1982 Endolithic microorganisms in the Antarcticcold desert Science 2151045ndash1053

Frisch T and Thorsteinsson R 1978 Haughton astrobleme A mid-Cenozoic impact crater Devon Island Canadian ArcticArchipelago Arctic 31108ndash124

Gold W G and Bliss L C 1995 Water limitations and plantcommunity development in a polar desert Ecology 761558ndash1568

Golubic S Friedmann E I and Schneider J 1981 The lithobionticecological niche with special reference to microorganismsJournal of Sedimentology and Petrology 51475ndash478

Graup G 1999 Carbonate-silicate liquid immiscibility upon impactmelting Ries Crater Germany Meteoritics amp Planetary Science34425ndash438

Grieve R A F 1988 The Haughton impact structure Summary andsynthesis of the results of the HISS project Meteoritics 23249ndash254

Grieve R A F and Pesonen L J 1992 The terrestrial impactcratering record Tectonophysics 2161ndash30

Grieve R A F Sharpton V L and Stˆffler D 1990 Shockedminerals and the KT controversy EOS 711792

Gurov Ye P and Gurova Ye P 1983 Zakonomernostirasprostraneniya razlomov vokrug meteoritnykh kraterov (naprimere kratera Elrsquogygytgyn) Laws of distribution of faultsaround a meteor crater example of Elgygytgyn Crater DokladyAkademii Nauk SSSR 2691150ndash1153

Henkel H 1992 Geophysical aspects of meteorite impact craters ineroded shield environment with special emphasis on electricresistivity Tectonophysics 21663ndash89

Hickey L J Johnson K R and Dawson M R 1988 Thestratigraphy sedimentology and fossils of the Haughtonformation A post-impact crater-fill Devon Island NWTCanada Meteoritics 23221ndash231

Hoppert M Flies C Pohl W Gcedilnzl B and Schneider J 2004Colonization strategies of lithobiontic microorganisms oncarbonate rocks Environmental Geology 46421ndash428

Ivanov B and Deutsch A 2002 The phase diagram of CaCO3 inrelation to shock compression and decompression Physics of theEarth and Planetary Interiors 129131ndash143

Johnston C G and Vestal J R 1989 Distribution of inorganic speciesin two Antarctic cryptoendolithic microbial communitiesGeomicrobiology Journal 7137ndash153

Jones A P Claeys P and Heuschkel S 2000 Impact melting ofcarbonates from the Chicxulub Crater In Impacts and the EarlyEarth edited by Gilmour I and Koeberl C Heidelberg Springer-Verlag pp 343ndash361

Kieffer S W 1971 Shock metamorphism of the Coconino sandstoneat Meteor crater Arizona Journal of Geophysical Research 765449ndash5473

Kieffer S W 1975 From regolith to rock by shock The Moon 13301ndash320

Kieffer S W Schaal R B Gibbons R Hˆrz F Milton D J andDube A 1976a Shocked basalts from Lonar impact crater Indiaand experimental analogues Proceedings of the Lunar ScienceConference 71391ndash1412

Kieffer S W Phakey P P and Christie J M 1976b Shock processesin porous quartzite Transmission electron microscopeobservations and theory Contributions to Mineralogy andPetrology 5941ndash93

Kivekpermils L 1993 Density and porosity measurements at thepetrophysical laboratory of the Geological Survey of Finland InGeological Survey of Finland Current Research 1991ndash1992edited by Autio S Special paper 18 Finland Geological Surveyof Finland pp 119ndash127

Koeberl C 2004 Tektite origin by hypervelocity asteroidal orcometary impact Target craters source craters and mechanismsIn Large meteorite impacts and planetary evolution II edited byDressler B O and Sharpton V L Special paper 339 BoulderColorado Geological Society of America pp 133ndash152

Koeberl C Rampino M R Jalufka D A and Winiarski D H 2003A 2003 expedition into the Libyan Desert Glass strewn fieldGreat Sand Sea Western Egypt (abstract 4079) ThirdInternational Conference on Large Meteorite Impacts CD-ROM

Kukkonen I T Kivekpermils L and Paananen M 1992 Physicalproperties of kpermilrnpermilite (impact melt) Tectonophysics 216111ndash122

Kurtz H D and Netoff D I 2001 Stabilization of friable sandstonesurfaces in a desiccating wind-abraded environment of south-central Utah by rock surface microorganisms Journal of AridEnvironments 4889ndash100

Le Campional-Sumard T Golubic S and Hutchings P 1995Microbial endoliths in skeletons of live and dead corals MarineEcology Progress Series 117149ndash157

Lim D S S and Douglas M S V 2003 Limnological characteristicsof 22 lakes and ponds in the Haughton Crater region of DevonIsland Nunavut Canadian High Arctic Arctic Antarctic andAlpine Research 35509ndash519

Maxwell J B 1981 Climatic regions of the Canadian Arctic islandsArctic 34225ndash240

Melosh J 1989 Impact crateringmdashA geologic process OxfordOxford University Press 245 p

Osinski G R and Lee P 2005 Intra-crater sedimentary deposits at theHaughton impact structure Devon Island Canadian High ArcticMeteoritics amp Planetary Science 40 This issue

Osinski G R and Spray J G 2001 Impact-generated carbonatemelts Evidence from the Haughton Structure Canada Earth andPlanetary Science Letters 19417ndash29

Osinski G R and Spray J G 2003 Evidence for the shock meltingof sulfates from the Haughton impact structure Arctic CanadaEarth and Planetary Science Letters 215357ndash370

Osinski G R and Spray J G 2005 Tectonics of complex craterformation as revealed by the Haughton impact event DevonIsland Canadian High Arctic Meteoritics amp Planetary Science40 This issue

Osinski G R Grieve R A F and Spray J G 2004 The nature of thegroundmass of surficial suevites from the Ries impact structureGermany and constraints on its origin Meteoritics amp PlanetaryScience 391655ndash1683

Osinski G R Spray J G and Lee P 2005b Impactites of theHaughton impact structure Devon Island Canadian High ArcticMeteoritics amp Planetary Science 40 This issue

Osinski G R Lee P Spray J G Parnell J Lim D S S Bunch T E


Cockell C S and Glass B 2005a Geological overview andcratering model of the Haughton impact structure Devon IslandCanadian High Arctic Meteoritics amp Planetary Science 40 Thisissue

Parkes R J Webster G Cragg B A Weightman A J NewberryC J Ferdelman T G Kallmeyer J Joslashrgensen B B AielloI W and Fry J C 2005 Deep sub-seafloor prokaryotesstimulated at interfaces over geologic time Nature 436390ndash394

Parnell J Lee P Cockell C S and Osinski G R 2004 Microbialcolonization in impact-generated hydrothermal sulphatedeposits Haughton impact structure and implications forsulphates on Mars International Journal of Astrobiology 3247ndash256

Perry R S Engel M H Botta O and Staley J T 2003 Amino acidanalyses of desert varnish from the Sonoran and Mojave desertsGeomicrobiology Journal 20427ndash438

Pesonen L J Elo S Lehtinen M Jokinen T Puranen R andKivekpermils L 1999 Lake Karikkoselkpermil impact structure centralFinland New geophysical and petrographic results In Largemeteorite impacts and planetary evolution II edited by DresslerB O and Sharpton V L Special paper 339 Boulder ColoradoGeological Society of America pp 131ndash147

Pesonen L J Mader D Gurov E P Koeberl C Kinnunen K ADonadini F and Handler R 2004 Paleomagnetism and 40Ar39Ar age determinations of impactites from Ilyinets structureUkraine In Cratering in marine environments and on ice editedby Dypvik H Burchell M and Claeys P Berlin Springer-Verlag pp 251ndash280

Pilkington M and Grieve R A F 1992 The geophysical signaturesof terrestrial impact craters Reviews of Geophysics 30161ndash181

Plado J Pesonen L J Koeberl C and Elo S 2000 The Bosumtwimeteorite impact structure Ghana A magnetic modelMeteoritics amp Planetary Science 35723ndash732

Plado J Pesonen L J Elo S Puura V and Suuroja K 1996Geophysical research on the Kpermilrdla impact structure HiiumaaIsland Estonia Meteoritics amp Planetary Science 31289ndash298

Pohl J Eckstaller A and Robertson P B 1988 Gravity andmagnetic investigations in the Haughton impact structure DevonIsland Canada Meteoritics 23235ndash238

Quesada A Vincent W F and Lean D R S 1999 Community andpigment structure of Arctic cyanobacterial assemblages Theoccurrence and distribution of UV-absorbing compounds FEMSMicrobiology Ecology 28315ndash323

Raven J A Kubler J E and Beardall J 2000 Put out the light andthen put out the light Journal of the Marine Biology Associationof the UK 801ndash25

Roberston P B and Sweeney J F 1983 Haughton impact structureStructural and morphological aspects Canadian Journal ofEarth Sciences 201134ndash1151

Saiz-Jimenez C Garcia-Rowe J Garcia del Cura M A Ortega-Calvo J J Roekens E and van Grieken R 1990 Endolithiccyanobacteria in Maastricht Limestone Science of the TotalEnvironment 94209ndash220

Salminen J 2004 Petrophysics and paleomagnetism of Jpermilnsijpermilrviimpact structure MSc thesis University of Helsinki HelsinkiFinland In Finnish

Schlesinger W H Pippen J S Wallenstein M D Hofmockel K SKlepeis D M and Mahall B E 2003 Community composition

and photosynthesis by photoautotrophs under quartz pebblesSouthern Mohave Desert Ecology 843222ndash3231

Scott D and Hajnal Z 1988 Seismic signature of the Haughtonstructure Meteoritics 23239ndash247

Smith M C Bowman J P Scott F J and Line M A 2000Sublithic bacteria associated with Antarctic quartz stonesAntarctic Science 12177ndash184

Sterflinger K and Krumbein W E 1997 Dematiaceous fungi as amajor agent for biopitting on Mediterranean marbles andlimestones Geomicrobiology Journal 14219ndash230

Svoboda J 1977 Ecology and primary production of raised beachcommunities Truelove Lowland In Truelove Lowlands DevonIsland Canada A high arctic ecosystem edited by Bliss L CEdmonton University of Alberta Press pp 185ndash216

Thorseth I H Furnes H and Heldal M 1992 The importance ofmicrobiological activity in the alteration of natural basaltic glassGeochimica et Cosmochimica Acta 56845ndash850

Thorsteinsson R and Mayr U 1987 The sedimentary rocks of DevonIsland Canadian Arctic Archipelago Geological Survey ofCanada Memoir 411 Ottawa Geological Survey of Canada182 p

Tribollet A and Payri C 2001 Bioerosion of the coralline algaHydrolithon onkodes by microborers in the coral reefs ofMoorea French Polynesia Oceanologica Acta 24329ndash342

Vogel S 1955 Niedere ldquoFensterpflanzenrdquo in der scedildafrikanischenWcedilste ein oumlkolosische Schilderung Beitrpermilge zur Biologie derPflanzen 3145ndash135

Walker B D and Peters T W 1977 Soils of the Truelove lowlandand plateau In Truelove Lowland Devon Island Canada A higharctic ecosystem edited by Bliss L C Edmonton University ofAlberta Press pp 31ndash62

Warscheid T and Krumbein W E 1994 Biodeterioration processeson inorganic materials and means of countermeasures Materialsand Corrosion 45105ndash113

Wellsbury P Goodman K Barth T Cragg B A Barnes S P andParkes R J 1997 Deep marine biosphere fuelled by increasingorganic matter availability during burial and heating Nature 388573ndash576

Wessels D C J and Bcedildel B 1995 Epilithic and cryptoendolithiccyanobacteria of Clarens sandstone cliffs in the Golden GateHighlands National Park South Africa Botanica Acta 108220ndash226

Werner S C Plado J Pesonen L J Janle E and Elo S 2002Potential fields and subsurface models of Suvasvesi Northimpact structure Finland Physics and Chemistry of the Earth 271237ndash1245

Westall F and Folk R L 2003 Exogenous carbonaceousmicrostructures in Early Archaean cherts and BIFs from the IsuaGreenstone Belt Implications for the search for life in ancientrocks Precambrian Research 126313ndash330

Whitehead J Spray J G and Grieve R A F 2002 Origin ofldquotoastedrdquo quartz in terrestrial impact structures Geology 30431ndash434

Whitlock C and Dawson M R 1990 Pollen and vertebrates of theearly Neogene Haughton Formation Devon Island ArcticCanada Arctic 43324ndash330

Wierzchos J Ascaso C Sancho L G and Green A 2003 Iron-richdiagenetic minerals are biomarkers of microbial activity inAntarctic rocks Geomicrobiology Journal 2015ndash24


communities can influence weathering (Warscheid andKrumbein 1994) and rates of biogeochemical cycling(Johnston and Vestal 1989) Furthermore discrete ecosystemscan become established within rocks allowing for elementalcycling and nutrient gradients which benefit many differentmicroorganisms (Friedmann 1982)

Asteroid and comet impacts generate pressures andtemperatures that can vaporize melt shock metamorphose

andor deform a substantial volume of the pre-impact targetsequence (eg Grieve and Pesonen 1992) This profoundinfluence on target materials can change the availability andcharacteristics of habitats for lithophytic organisms (Cockellet al 2002) As impact events are a universal phenomenonand would have been more frequent on the early Earth thantoday understanding their influence on habitats formicroorganisms is a fundamental objective in microbiology

In this paper we use data gathered at the Haughtonimpact structure Nunavut Canada in combination with datafrom other craters to develop a synthetic understanding of theeffects of impact on habitats for lithophytic organisms

BIOLOGICAL CHARACTERISTICS OF THE FIELD SITE

The Haughton impact structure is located on DevonIsland Nunavut Canadian High Arctic and is centered at75deg22primeN and 89deg41primeW By geophysical criteria the structurehas an apparent diameter of about 24 km (Pohl et al 1988)

Table 1 Habitats for lithophytic organisms and some of the effects of asteroid and comet impacts on their abundance and characteristics (nomenclature after that of Golubic et al 1981)

Name of habitat Description of habitatEffects of impact at Haughton General effects of impacta

Cryptoendolithic Habitat within the interior of the rock

Increase in interconnected pore spaces in shocked gneiss and increase in translucence results in greater habitat availability

Impact-induced fractures and pore space is likely to increase interior space for colonization in many rock types However photosynthetic endoliths require light penetration Impact alteration of rock translucence may change availability of habitat

Chasmoendolithic Habitat in fissures and cracks within rock

Increase in habitats caused by fracturing of rocks General to many rock types characterized in dolomite

Impact-induced fractures and fissures are likely to make an increase in chasmoendolithic habitat a common occurrence in impact structuresb

Euendolithic Habitat formed by active boringpenetration by microorganisms

Euendolithic organisms not studied However habitat (carbonates) form immiscible melts with other target materials

Increase in pore space caused by shock or changes in density of rock and rock chemistry (eg heterogeneous carbonate melts) could plausibly affect the ease with which microorganisms can actively penetrate into rocks

Epilithic Habitat on surface of rocks


The habitat on the surface of rocks will generally be unaffected by impact However two possible modes of change in suitability for colonization could be 1) changes in weathering rates caused by mineralogical changes eg melting could cause changes in the abundance of surface attachment sites (eg caused by changes in surface roughness) or 2) changes in macronutrient availability might change suitability of rock surfaces for microbial biofilm formation

Hypolithic Habitat on underside of rock


The habitat on the underside of rocks will generally be unaffected by impact A possible instance in which hypolithic habitat availability could be changed would be alterations in the translucence of rocks (for example the formation of impact glasses in desert settings) which would alter suitability of underside of rocks for photosynthetic hypoliths

aHabitat availability can be changed by for example the emplacement of a melt sheet (ejecta blanket) over previously available lithic habitats The impact meltbreccia hills of the Haughton impact structure cover Palaeozoic dolomite which in other regions of Devon Island and the High Arctic provide abundanthypolithic habitat (Cockell and Stokes 2004) However in this paper we focus on the direct effects on rocks caused by shock metamorphism

bCyanobacterial chasmoendoliths have recently been reported from shocked limestones in the Ries impact structure (Cockell et al 2004)

Fig 1 Lithic habitats (see Table 1 for descriptions)










































































EPILITHIC HABITATS






HYPOLITHIC HABITATS















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EPILITHIC HABITATS






HYPOLITHIC HABITATS















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HYPOLITHIC HABITATS















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