84 Chapter 6

Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.

Chapter 6

The Origin of Earth and Life

6.1 Introduction

If life is ever to achieve planet-changing stature, it mustfirst start on the planet. It happened on Earth. Butexactly how it happened remains a frustrating mystery.We cannot go back in time to witness the origins of lifeon our world. So scientists must approach this problemas a detective would. What are the reasonablepossibilities? Where does one start to look for clues?

All active pursuits in this field have traced the origin oflife back to some kind of chemical moment. The originof life’s chemistry marks the origin of life. Soinvestigators wonder about modern biochemistry’sorigins. How did molecules ‘learn’ to self-organize? Howdid they ‘learn’ to copy their stores of information tonew molecules?

Life is matter that is animated in very purposeful ways.The self-assembly and replication phenomena representthe ascent of matter from slave of the physical world tothe level of purposeful entity that exploits the physicalworld. Overall, there is no built-in OFF button. Oncemolecules begin to self-assemble, they will continue todo so as long as their surrounding physicalenvironment permits it. The more gracious theirenvironment, the more living molecules will do theirthing – becoming more abundant as a result. And asliving matter becomes more abundant, its impact on theplanet will increase.

Let’s consider the theories. It turns out that newerunderstandings of the primordial Earth have cast doubton some old favorites. For example, the famous Oparin-Haldane primordial soup idea captivated severalgenerations of scientists in the twentieth century. Thisidea is very dependent upon a particular mix of gases inthe Earth’s early atmosphere. New findings about theearly atmosphere mean this once most popular view, ishighly unlikely. Other creative ideas dependent upon acertain kind of early atmosphere also have fallen victim.So, right from the very beginning, we must think of lifein the context of the whole planet. In spite of thesesetbacks, science continues its search.

Also, you will quickly discover that science is far awayfrom an answer to this most interesting question. Butthat is not the point. What is most interesting is howpersistent human minds are unwilling to give updespite formidable odds. Trying to solve a mystery that

happened over 3.8 billion years ago is not easy, andmay be altogether impossible. Yet scientists never stopwondering about new possibilities, searching for newclues, and scouring their data for some overlookeddetail. The human mind directs this quest, but it isconsistent with the notions about life in general. Life isan activity that prepares innovative experiments, someof which lead to successful solutions in the struggle forsurvival. In this sense, creative innovation literally is away of life. Why should the human mind act otherwise?

6.2 Physicists theorize that the Universe began with abang

Cosmologists believe the Universe began about 15billion years ago in what is popularly known as the BigBang. The Big Bang theory proposes that the firstelements in the Universe consisted of hydrogen (fig. 6.1)

and maybe helium.These simplemolecules are notmuch good formaking up life. Notjust yet. Still, theoriginal hydrogenatoms perhapsplayed a very crucialrole in thedevelopment of theUniverse. Visualizethe Universe, say, abillion years afterthe big bang.

According to this model, it was nothing more than adark cloud of hydrogen gas rapidly expanding. TheUniverse is hard to imagine at this stage because it wasdark, absolutely. What is missing? Stars.

The stars in the night sky, and the huge one in ourdaytime sky are thought to have been formed from thehydrogens interrupted by gravity from their race acrossspace. Our understanding is that the first stars couldhave formed following the development of eddies in theflow of the universal wind. These eddies could haveestablished opportunities for density differences in thecloud. That is, the cloud could become thicker in someparts and thinner in others. In the thicker parts,gravitational pull between all of the congregatinghydrogens would have started to grow stronger, pulling

Figure 6.1. After the Big Bang, matterin the universe consisted mainly ofhydrogen (nuclei shown here) andhelium atoms.

The Origin of Earth and Life 85Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.the hydrogen atoms toward the centers of these eddies.As more hydrogens were pulled closer, the gravitationalpull would increase, pulling still more hydrogens in atfaster and faster speeds. So, little disruptions in thecloud (like eddies) could have served as focal points forthe concentration of hydrogen gas in a still very darkplace. But a dense hydrogen pocket does not a starmake.

In the process of star-making, two main ingredients arerequired:• trillions and trillions of tons of hydrogen gas• gravitation that pulls these hydrogen atoms tighter

and tighter together

The gravitation exerted by all of the hydrogen atoms oneach other eventually could have caused the cloud tocollapse in all directions, forming a discrete sphere, theprecursor of a star (protostar). As this ball collapsed stillmore, temperatures in the millions of degrees could begenerated, stripping hydrogen atoms of their electrons.The continuing build up of pressure by the collapsingball eventually can force the bare hydrogen atoms(protons) to fuse to each other. This fusing actionproduced the first flickers of light in the foggy dungeonof the big bang.

When hydrogen protons stick together, this is what isknown as a nuclear fusion reaction. It is the same kindof reaction humans used to create the hydrogen bomb.In this reaction, hydrogen protons fuse together tomake the nucleus of a new element, helium. In the

process of fusing,tremendous amounts ofenergy are released inthe form ofelectromagneticradiation (part of itsspectrum includes arange of frequencies weinterpret as ‘light’), heatand explosive force.When the first rays oflight begin to emergefrom a collapsingprotostar, the collapsehalts, balanced by theoutward push of billions

of nuclear fusion reactions. So, a star actually exist in asteady balance. On the one hand it wants to collapseunder the crush of its own weight, but is buoyed out onall sides by the force of internal nuclear explosions. Onthe other hand, it wants to explode outward into space,but is held tight at all quarters by its own immensegravity.

For stars, a standoff is reached between two competingforces, gravity and nuclear explosions. But gravity willwin in the end. Still, this struggle can last for onemillion to 10 billion years or more, depending upon the

size of the star. In the meantime, these warriors ofphysics shower nearby space with light and heat. Andwhen stars appeared, the universe for the first time wasilluminated with exciting possibilities (fig. 6.2).

But living things and even rocks are made up not onlyof hydrogen, but of carbon and nitrogen, oxygen andmore. Today, there are over 100 elements. But in theearly universe, these elements did not exist — onlyhydrogen and helium. Then, there was no possibility ofplanets, nothing to make dirt out of. So, the familiar soilupon which we walk wasn’t made at the time of the bigbang. It came much later — after the death of stars.

6.3 Planets formed from the debris spewed into spacefrom exploding stars

Even for stars, as with so many things, all good thingsmust end. Some time between 1 million years (for reallybig stars) and hundreds of billions of years (for verysmall stars – if the Universe lasts that long), thehydrogen fuel is used up. No longer inflated by nuclearreactions, the star will begin to collapse under it ownimmense gravity. As the star contracts, the helium corecan heat up to 100 million °C and hotter. In addition,greater pressures are generated at the star’s core by thecontracting mass. The combination of highertemperatures and pressures can be sufficient to renewnuclear reactions for awhile. But this time the productsare not just helium. Instead, helium nuclei are forcedtogether to make new elements like carbon, oxygen,nitrogen and others. This is followed by a series of morestellar contraction events yielding higher temperatures,pressures and even heavier elements like lead and gold.The sequence of contraction and element synthesis caninvolve many cycles, each time producing heavier andheavier elements. The result is that the dying star’s corebecomes layered like the inside of an onion. The layerscontain progressively heavier and heavier elements, theheaviest of which are found at the center. Weighty with

a diversity of elements,the aged star now ispoised to bear forth thecosmic seeds of planets.

If the star is about 1-1/2 times the size of oursun, it could experienceone final mightycollapse and then acosmic explosion – asupernova (fig. 6.3).This explosion ejectsmuch of the star’s corematerials into space,sometimes leavingbehind a small core

Figure 6.2. The first stars formedout of hydrogen atomscompressed by immense gravity.

Figure 6.3. The Crab Nebula isthe aftermath of an exploding star.Coutesy NASA.

86 Chapter 6

Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.remnant – a neutron star. The materials spewed fromthe star form a large, colorful cloud much larger thanour solar system, called a nebula (fig. 6.3).

Cosmologists propose that our sun and the planets inour solar system could have formed from the nebularremains of an exploding star. Evidence that this canhappen has been seen with the Hubble Space telescope.The Hubble telescope has observed disks of dustsurrounding at least half the stars in the nearby Orionnebula. According to this theory of planet formation, thenebular gases began to collect once again into aprotostar which was to become our sun. But this timethe surrounding gases were composed of not only ofhydrogen and helium. Instead, they were filled with atreasure of planet-building elements. As portions of theancestral star’s element-rich nebular cloud swirledaround our newly-created proto-sun, eddies ofgravitation were once again developed (fig. 6.4). Thegravitational turbulence around the sun perhaps

caused the cloud particles to collect into sphericalobjects swirling around the sun. In the first stages,there could have been dozens of heavenly bodiescompeting for orbital territory. Sometimes merging,sometimes exploding under the battle of cosmiccollisions. The final nine planets of our solar system (fig6.5) are the victors of the orbit war, the end of whichhas been followed by a lasting peace (occasionallyinterrupted by persistent debris like asteroids andcomets). Such a calm and generally stable environmentwas necessary for construction of the complex livingsystems that soon followed.

6.4 Earth�s early atmosphere and overall environmentinfluenced the way life could have started

Biologists think that life started on Earth as early as 3.8billion years ago. The question is, what was the Earth’satmosphere like back then? In the first half of the 20thcentury, scientists believed that the earliest atmospherecontained mostly carbon dioxide (in the air you breatheout), methane (what we call natural gas), ammonia (agood cleaner), and hydrogen gas (used in the oldblimps). This view of the atmospheric composition wasnecessary to support certain popular life origin ideas(namely the Oparin-Haldane idea, discussed below).

However, in the 1950s, the understanding of theprimordial atmosphere began to change, and it had todo with where the gases came from in the first place.There was a growing understanding among geologiststhat the gases in the atmosphere came from within theEarth itself — from volcanoes. Geochemists, ClaudeAllegre’ and colleagues, have determined that nearly allof the atmosphere was made by the time the Earth wasa mere one million years old (Earth is believed to beabout 4500 million years old). Its composition was verymuch different from what was previously thought.According to this view, it was mostly carbon dioxide andnitrogen (fig. 6.6). There might have been very smallamounts of methane, ammonia, and almost no freehydrogen gas was present. Let’s see how the kinds ofgases in the atmosphere can influence the origin of life.

Figure 6.5.Planets of the Solar System

Figure 6.4. Side-on scan of the planet-forming disk of star, BetaPictoris. Courtesy NASA.

M E R C U RY

V E N U S

EA RT H

M A R S

JU P IT ERS ATU R N

U R A N U S

N E P TU N E

PLU TO

The Origin of Earth and Life 87Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.

6.5 The mix of gases in an atmosphere can powerfullyinfluence the chemistry of life

Biologists who study the origin of life are very interestedin the chemical composition of the original atmosphere.This is because nearly all origin ideas start at the levelof chemical reactions. The chemistry of the atmospherecan powerfully influence the chemistry of life. Forexample, I hope you noticed that the earliestatmosphere had no molecular oxygen (a molecule inwhich two atoms of oxygen are stuck together).Molecular oxygen is what we seek when we inhale.

The absence of molecular oxygen was very important forthe early chemistry of life because ironically, molecularoxygen is very destructive to other molecules. Molecularoxygen is very reactive and tends to break othermolecules apart. It does this by reacting with them tomake something else. This is bad news for defenselessmolecules in the open environment. No doubt you haveseen the effects of oxygen gas on your car’s paint.Oxidized paint has been destroyed by reactions withoxygen gas. If oxygen can damage something as ruggedas car paint, think what it can do to delicate littlemolecules floating in water. It pulverizes them. In a highoxygen atmosphere, it is very unlikely that themolecules of life could undergo the kinds of buildingprocesses necessary to lead to a living thing. Oxygenwould destroy them each step of the way, and noprogress would be made.

So, it was probably a very good thing that the earlyatmosphere had no free oxygen gas. The earliestmolecules could accumulate and react with one anotherin a safe environment without being “harassed” byoxygen. Why doesn’t molecular oxygen harm livingthings now? It can, but living things have a defensesystem. It is called aerobic cellular respiration. In later

chapters we will learn the astonishing story about howaerobic cellular respiration helped the spread of life byharnessing and benefiting from the destructive power ofoxygen.

There is much more to learn about the atmosphere’sexciting connection with the development of life and theplanet. I will cover more on this topic in later chapters.

6.6 Scientists are uncertain how life began on Earth.

We do not know how life actually got started on Earth.You may find this hard to believe, but biologists are stillvery far away from understanding how life began onthis planet. There are some popular ideas, but they arevery incomplete and untested. That stuff you haveheard about the old primordial soup? Maybe it’s right.Probably it’s not. I think it is important for you tounderstand that, in spite of all its technological bluster,modern scientific work still is unable to answer manyvery fundamental questions. The origin of life is one ofthese unanswered questions. That is not to sayscientists are not trying. Some scientists have spentmuch of their careers seeking the answer to this mostinviting mystery. But we are not sure if their productivework has led to progress. There are so many paths thatcould lead back to life’s origins. Which is the one truepath we may never know. For now, let’s focus on thedifferent ideas science has on the origin of life on Earth.

6.7 The Oparin-Haldane hypothesis depends upon anunlikely atmosphere

In the 1920s, Soviet scientist Alexander Oparin andEnglish scientist J. B. S. Haldane independentlyproposed an hypothesis on the origin of life. It was laterto be popularly known for its “primordial soup” idea.The Oparin-Haldane hypothesis was the first trulymodern idea on the origin of life, and it has been widelyadopted by biologists (but is probably dead wrong).Their hypothesis was modified through the years, andin the early 1950s it was endorsed by Nobel Prizechemist Harold Urey. The hypothesis can besummarized as follows:1. When life began, Earth had an atmosphere that was

composed of the mostly methane (like the naturalgas you use in your stove), ammonia (like the stuffyou use to clean your floors with), hydrogen (likethe gas that kept the early blimps afloat, includingthe ill-fated Hindenberg that exploded), and water(fig. 6.7). There was no free molecular oxygen (O2) inthe atmosphere.

2. Lightning, ultraviolet radiation from the sun, andvolcanic heat energized reactions involving thegases in the atmosphere. This led to the formationof carbon molecules. Living things are made fromcarbon molecules.

What, no oxygen?Figure 6.6. Volcanic eruption. Earth scientists now believe that theEarth's atmosphere was the product of volcanoes. Along withhuge amounts of dust particles, volcanoes spew out gases --mainly water vapor, carbon dioxode, and molecular nitrogen (N

2).

The carbon dioxide may have acted like a thermal blanket to helpkeep the planet warm because the sun was much cooler when lifebegan.

88 Chapter 6

Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.3. As Haldane put it, these new molecules “must have

accumulated until the primitive oceans reached theconsistency of a hot dilute soup.”

4. Later changes amongst the molecules in the soupled to the formation of life.

This idea enjoyed widespread popularity in the 20thcentury. However, we now know it has problems thatare probably fatal. For example, the conventionalwisdom amongst geologists today is that the Earth’searly atmosphere was much different than the oneproposed by Oparin-Haldane. That is, it was high inwater vapor, carbon dioxide and nitrogen. There is littlesupport for the presence of methane, ammonia, ofhydrogen which was proposed in the Oparin-Haldanehypothesis. There are additional questions regardingthe longevity of the so-called prebiotic soup. Forexample, geologist Lars Gunnar Sillen predicts thateven if there was an Oparin-Haldane atmosphere, anymolecules in solution would not last long. They wouldquickly re-convert back to the original atmosphericgases. Why is this a problem? If they didn’t re-convertback, chemist Arie Nissenbaum suggests that instead offloating free, the molecules would be deposited on theocean floor in gooey tars or tied up in reactions withminerals. Such fates would virtually eliminate thepossibility of chemical reactions leading to life.

Given these shortcomings, the Oparin-Haldane idearightly has lost much support in the scientificcommunity. But there is another idea that dovetails intothe Oparin-Haldane hypothesis. It is called the Miller-Urey experiment.

6.8 The Miller-Urey experiment also assumes an unlikelyatmosphere

Stanley Miller was a graduate student at the Universityof Chicago in 1952. Under the guidance of his researchadvisor, Professor Harold Urey, Miller performed anexperiment whose outcome would capture theimagination of the biological world. Stanley Millerwondered if a mixture of Oparin-Haldane gases couldlead to the formation of the molecules of life. This wasan idea that invited Miller to experiment. So, he setabout to design an apparatus to help him test this

seductive idea. His apparatus can best be described asa large hollow tube of glass that was bent into a circleand connected at both ends. This established a totallyenclosed environment inside the tube. Miller then addedwater and a mixture of the Oparin-Haldane gases,methane, ammonia, and hydrogen. He attachedelectrodes that made sparks inside the tube. This wasto simulate lightning on early Earth. He let hisexperiment run for a week. After this period of time, henoticed a tarry substance coating the inside of the tube.When he analyzed it for its contents, he found smallamounts of two simple amino acids, alanine andglycine. Amino acids are the building block moleculesfor larger molecules called proteins (proteins are veryimportant in living things). When Miller announced hisfindings, the scientific community flocked to declare its

Glycine (CH NH COOH)(an amino acid)

2 2

Methane (CH )4

Ammonia (NH )3

Hydrogen (H )2

2Water (H 0)

Figure 6.7. A drawing depicting the reactions of the Oparin-Haldane primordial soup. The main product is a simple aminoacid. Amino acids are building block molecules used by life tomake proteins. The big problem with this idea right now is that theatmosphere upon which it is based is considered highly unlikely.

Figure 6.8. A drawing of a sectionof DNA. DNA is the molecule thatcarries the genetic code in livingthings. Two properties make this themost powerful of all biologicalmolecules. They are: 1) it can makecopies of itself; and 2) its sequenceof building blocks can be rearrangedlike the letters in an alphabet,enabling it to be a carrier of codedinformation.

The Origin of Earth and Life 89Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.support. For here was an experiment that, in theirminds, demonstrated that forming the molecules of lifewas possible on early Earth. But let’s be scientists for aminute here.

If we study the Miller-Urey as skeptical scientists, wewill find that it is not all that remarkable. We will alsolearn that making a few amino acids in a test tube fallsfar short of synthesizing complex molecules of life, likeDNA (fig. 6.8). The main problems with this experimentare summarized below:1. The initial gas mixture was based on the Oparin-

Haldane atmosphere. This gas mixture in the earlyatmosphere now is thought to be highly improbableby geologists.

2. The first design of the experimental apparatusproduced no amino acids. After he modified theorganization of different parts of the apparatus,Miller achieved the desired outcome. Other attemptsto “improve” the design also failed to produce aminoacids. Small variations produced no amino acids.The problem with this is that the sensitiveeccentricities of the experimental apparatus are notwidely communicated. What does this tell you aboutthe “inevitability” of the process on early Earth? Asa result, the Miller experiment has seriously misledmany students and prominent scientists alike.

3. The presence of simple amino acids is not reallyrelevant to the origin of life. This is because in orderfor life to work, molecules must be able to makecopies of themselves. Nucleic acids, like DNA can dothis. There is no evidence that amino acids or theirprotein constructs have any ability to self-replicate.If we cannot find copying abilities in amino acids,linking the Miller-Urey experiment to the origin oflife issue, is scientifically risky.

6.9 Leslie Orgel suggests that the first replicators mayhave been RNA, but then again...

Leslie Orgel advocates the idea that RNA molecules (orsimilar variants) may have been the first replicators.The term, RNA, stands for “ribonucleic acid”. RNA (fig.6.9) is a cousin to DNA, the master replicator. For now,let’s think of RNA as a very large molecule like a kind ofchain of smaller units or “links”. Orgel’s vision is thatRNA could have spontaneously assembled in theprebiotic world. This could have been done as each ofthe links, already present, came together to form a longthread of RNA. What makes RNA so interesting is not somuch that it is a chain of smaller molecules, but thateach of the links has an attraction for an “opposite” link- like the teeth of a zipper. This is a property that makesit possible for RNA to duplicate itself. So, if a singlestrand of RNA is present, then each of its links attractsa complimentary link which comes out of the prebioticsoup. It would be like building a zipper by starting withonly one side of the zipper, then placing it in a pan offree zipper teeth. The free zipper teeth then encounter

and stick to the zipper half, forming a new strand ofzipper. The result is two complete zipper strands. Thereis a problem here though. The second half of the zipperisn’t a duplicate, it’s a mirror image. So the processwould have to be repeated, this time using the newlyformed zipper half as the template to make yet anothernew zipper half. Orgel has successfully completed thefirst step of this copying process without the benefit ofhelping molecules called enzymes (kinds of proteins).But enzymes are needed in order to complete thesecond round of copying. The need for enzymes was tolead to another problem that I will discuss a little laterbelow.

The point is that RNA has the potential for being thefirst self-replicating molecule. But that’s not the onlyreason Orgel is interested in RNA. RNA also can carrycoded information. Remember that RNA is made up oflittle “link” molecules. These make up the chain of RNA.There are four different kinds of “link” molecules, likethere are different kinds of letters in the alphabet. RNAhas an alphabet of four letters. If you think of the linkmolecules like the letters in the alphabet can you seeRNA’s potential for carrying information? Codedinformation contained in molecules like RNA (inparticular, DNA) is used as a basis for making otherchain-type molecules called proteins. Proteins arepowerful molecules that have important functions inliving things. So, if Orgel is correct, RNA was the firstreplicating and information-containing molecule —possessing the two essential properties of life. But thereare some roadblocks to this idea.

Figure 6.9. A drawing of RNA (left). UnlikeDNA, which is a double-stranded molecule,RNA is a single strand. The first step inreplicating RNA is to make a mirror image ofthe original strand, shown on the right.

90 Chapter 6

Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.The RNA idea assumes an Oparin-Haldane atmosphere.As we saw above, it is increasingly doubtful that suchan atmosphere ever existed on Earth. Another problemhas to do with the sequence of the appearance of RNAand proteins. The synthesis and replication of RNAtoday happens with the help of proteins (enzymes). Butproteins are synthesized using the coded information inthe RNA (or DNA). This situation represent a chicken-or-egg problem that may be impossible to overcome.

Orgel and others continue to pursue variations of theRNA theme, drawn by its self-replicating andinformation-carrying properties. However, whether theyare on the right trail or a wild goose chase probablywon’t be known for many years to come.

6.10 Sydney Fox proposed that cells made out of proteinscame first.

The question on the origin of DNA (or RNA) has puzzledscientists for decades. It would make the field so muchsimpler if DNA (or RNA) actually was the first livingmolecule. It has all the characteristics that are neededto make a molecule “alive”. It has the interesting powerto make copies of itself (with the help of proteins). Butthere is a problem with assuming that DNA was the firstself-replicating molecule. This is because DNA, inaddition to being absolutely huge, is also an immenselycomplicated molecule. So, it seems unlikely that themarch of life on Earth was dependent upon the randomsynthesis of the first DNA molecule. The chances of this

happening are extremely low. Professor Sydney Fox ofthe University of Miami believes he has the answer toDNA (or RNA) - protein paradox. He thinks proteinscame first (see fig. 6.10 for a drawing of a protein).

In his world, Fox imagined lagoons filled with tinybubble-like structures he called microspheres. Eachmicrosphere was composed of a substance calledproteinoids. These were molecules that were somewhatsimilar to proteins but not quite the same. In his model,the proteinoids catalyze chemical reactions and formouter surfaces that act like cell membranes. The chainsof amino acids could self-replicate and, therefore, couldevolve. In the process, they were able to produce nucleicacids like DNA and RNA. The DNA (or RNA) then beganto evolve on its own.

There are many problems with Fox’s proposal, and mosthave to do with the natural chemical properties ofamino acids. Attempts to synthesize the proteinoidsaccording to his hypothesis have produced unusualcombinations of amino acids that do not resembleconventional protein chains. Attempts to synthesizemicrospheres proved marginally successful, as theytended to be extremely fragile to subtle changes in theirenvironment. Still, the microspheres did display a formof reproduction, a sort of crystalline budding property.Other interesting lifelike properties were displayed,including the fusing of microspheres and theexchanging of material. Fox claims that this propertydemonstrates the origin of “protosexuality”. Fox calledthese microspheres “protocells”, and proclaimed themto be the precursor to DNA-based organisms. Is it?Despite Fox’s exhaustive attempts to demonstrate thevalidity of his hypothesis, many biologists still find itincomplete.

6.11 Graham Cairns-Smith proposed a simpler idea lessdependent on the atmosphere

Scottish chemist Graham Cairns-Smith suggested thatperhaps the first living things on Earth were not basedon carbon, as they are today. Instead, he proposed inthe early 1980s that first life might have been a sort ofclay crystal formed in the mud (fig. 6.11). That is, abeing made out of silicon dioxide crystals. You arefamiliar with silicon dioxide crystals. Quartz rock is akind of silicon dioxide crystal. Mica is a mineral ofsilicon dioxide that is made in volcanic lavas. Micaforms in thin, transparent layers that can be peeledaway like flimsy sheets of glass.

Crystals are interesting because they are the result ofatoms naturally organizing themselves in very deliberatepatterns. For example, common table salt is acrystalline form of sodium chloride. In salt, sodium andchlorine atoms attach to each other in an alternatingpattern that leads to a three-dimensional lattice shapedlike a cube. Look at an individual salt crystal with amagnifying glass and you will see what I mean.

Figure 6.10. A stylized drawing of a protein.Proteins are made from chains of aminoacids. The sequence of amino acids inproteins is determined by the sequence ofbuilding blocks that make up DNA (thegenetic code). Proteins can be very largemolecules and take an infinite number ofshapes. Their function largely is determinedby their shape.

The Origin of Earth and Life 91Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.We know that mineral crystals have the ability to growby simply adding on to an existing crystal. If a growingcrystal breaks apart, the fragments of that crystal cancontinue to grow on their own. In a sense, this is self-replication, and it is a process that is essential for life.

Certain kinds of clays called kaolinite have theinteresting property of growing in thin layers. Cairns-Smith argues that the clay crystals began growing byadding layers to themselves, like adding pages to abook. The growing crystals competed with each other forresources as they grew. Some crystals would breakapart, wash downstream and settle in a new area wherethey would continue their growth and laterfragmentation.

In the early Earth proposed by this idea,the world would be populated bycommunities of competing clay “beings”.Eventually, these clay creations wouldbegin to incorporate carbon-basedmolecules into their living apparatus.One way to do this would be thesynthesis of DNA or RNA to augmentclay-based genes. In time there would bea transition period where carbon basedgenetic material (DNA or RNA) wouldbecome a suitable alternative to clay-based genes. Then, the move to carbon-based life would be complete. DNA wouldhave been created, and the march oforganic life could begin.

I have left out many details to this ideabecause it is not the purpose of thisbook to exhaustively treat competingnotions on the origin of life. Still, thereare elements in the Cairns-Smith modelthat are manageable by science andshould provoke continued investigation.First, it makes no assumptions aboutthe composition of Earth’s earlyatmosphere. This is a major problemwith other earth-based life hypotheses. Italso is founded on the simplest of crystalproperties, that they have the ability togrow and “reproduce”, by fragmentation.This property is a true nature of crystals,

and can be easily demonstrated. Reproduction is anessential property of life. Many of the basic ideas of thisproposal are testable in the laboratory or in the field.However, Cairns-Smith argues that the clay ideaprovides a preparatory path for the ultimate synthesisof DNA or RNA. But he does not present a complete ideaon how DNA came from clay.

The Smith-Cairns idea has not received widespreadacceptance in the scientific community. Maybe becauseit is so offbeat. Accepted or not, it is an interesting pieceof work because of its initial simplicity and testability.

Figure 6.11. Hot springs like this could havegiven rise to the first self-replicatingmolecules -- of silicon dioxide.

92 Chapter 6

Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.6.12 Svante Arrhenius suggested that microorganisms

were ejected from other life-bearing planets

With the apparent flight of support from the Oparin-Haldane hypothesis, and Miller-Urey experiment, there

has been renewed interest in the idea that lifearrived on Earth from some distant planet. It

started with Swedish chemist SvanteArrhenius in the early part of the 20th

century. He proposed thatmicroorganisms were ejected from life-

bearing planets and drifted throughspace. One of them encountered

Earth quite by accident andstarted life here. This ideafails for two main reasons.The odds of a singlemicroorganism happeningupon Earth areastronomically low. Also,

there is the matter of surviving the journey. Radiation,vaccum and intense cold definitely would present majorchallenges to biological molecules traveling in space. Ifunprotected, large biological molecules would bedestroyed. But if embedded deep inside a large rock,dormant microorganisms might have a chance. Ofcourse, then there’s the problem of surviving the fieryentry through the Earth’s atmosphere.

6.13 Crick and Orgel proposed a dramatic idea called�Directed Panspermia�

A variation of the cosmic seed idea was presented byrespected biologist Francis Crick and his colleagueLeslie Orgel. Crick is the co-discoverer of the structureof DNA. In their idea called “Directed Panspermia”,Crick and Orgel proposed that life actually originatedfirst on another planet outside our solar system a longtime ago. On this planet, a vast intelligent civilizationwas confronted with the realization that their sun soonwould expand into a Red Giant and reduce their worldto a burned out cinder. They failed in attempts to fly toother suitable worlds. The distances were too great andtravel time in the thousands of years. So, instead ofsending “people” (whatever they were), they decided todistribute the seeds of life itself, namely primitivebacteria. About 3.2 billion years ago, one of the shipsfrom this ancient civilization reached earth anddischarged its load of bacteria (fig 6.11). The rest ishistory.

WOW! Now, that’s a story! Reminds me of the planetKrypton. Ironically, even Crick himself believes hisproposal is farfetched. He states that his purpose inpresenting it was not to cultivate believers in thisscience fiction like drama. Instead, he wanted to recruitgreater interest on the problem of life’s origins. Why isthis idea not a valid hypothesis?

6.14 Hoyle and Wickramasinghe suggested that lifeoriginated elsewhere and colonized the comets of thesolar system

Sir Fred Hoyle and Chandra Wickramasinghe havepostulated a most complex cosmic connection. In thelate 1970s, they proposed that life also originatedelsewhere and it traveled to our part of the galaxy justas our solar system was forming. The Earth and therest of the inner solar system was too hot then. So,microorganisms in the form of bacteria, viruses, andbits of genetic material survived in the cooler outer solarsystem. There, the bits of life became incorporated intocomets (fig. 6.13) whose orbits kept them on the outerfringes of the solar system. From time to time a cometwould break free and start its descent toward the sun.On its journey, the comet would strike Earth anddeposit its long-held load of living material, establishinglife on the planet. Then, throughout Earth’s history,later comets would deposit different kinds of living

material, perhapschanging the courseof the evolution oflife.

Assessing this storyis extremely difficultsince it relies onspeculativeassumptionsregarding thepresence of organicsubstances incomets.

Despite theiringenious story

lines, all of these cosmic proposals fail to address theultimate question. How did life begin in the first place?Instead, they avoid the question by assuming that lifebegan elsewhere and was imported to Earth. As ascientist, I think these proposals ar interesting but hardto work with because they are difficult to test.

6.15 We are far away from a solution

It is important to note, as does Robert Shapiro in hisbook, Origins, a Skeptics Guide to the Creation of Life onEarth, that simply possessing some of the pieces to thepuzzle does not necessarily lead to life. That is, not allparts of a living thing are created equally. Some partsmay be easily fabricated in a thousand different ways.Others may need extremely specialized conditions. I amreminded of a wonderful Gary Larson cartoon where twocows are constructing what looks like a rocket ship outof discarded lumber. What makes this a joke is that wehumans know that rockets are enormously more

Figure 6.13. A comet striking theEarth at 50,000 miles per hour.

The Origin of Earth and Life 93Copyright© 1999 by Tom E. Morris. http://www.planetarybiology.com

This chapter is an excerpt from Principles of Planetary Biology, by Tom E. Morris.complex than a bunch of boards nailed together. Butthe cows don’t know this, and will be disappointedwhen, although their construct looks like a rocket tothem, it won’t fly.

For example, it may be possible to synthesize aminoacids in a hundred different ways. Stanley Miller justhappened to discover one of the ways. Which particularamino acid fabrication technique led to life may not beimportant. Stumbling on one of many fabricationtechniques for such simple compounds does notnecessarily lead down the path of life’s origin. Instead, itmay lead to a dull dead end. The same is true for clayreplicators and protocells. These may be almostunavoidable results that might be obtained in athousand different ways. Does the formation of aproteinoid sphere automatically point to life? It doesn’thave to. Maybe it does. Maybe not.

Some ideas claim they lead toward the development ofthe master replicator, DNA, almost as an inevitableoutcome of simple beginnings. We have to be carefulhere. Asking conservative scientific thinkers to makethe leap from simple amino acid to complex life armedonly with incomplete mechanisms and speculations isrisky. Nonetheless, scientist and lay person alike domake this leap, in spite of the enormous gaps in originideas. Maybe this is to be expected. Like all humans, weseek order in our universe, and not knowing about theorigin of life and ourselves is unsettling. Many findsolace by adopting one of the numerous explanationsoffered by religious philosophies. For science, thereremains healthy doubt regarding ideas on the origin oflife.

So, where does all this leave us? We have a long, longway to go. I believe that none of the ideas on thedevelopment of life on Earth is much more than apotential starting point. And there may be hundreds ofpotential starting points. It is possible that all of these

could ultimately lead to life. Or, only one of them will.How can we ever know? The only way to feel reallyconfident in such an idea is to actually demonstrate thesynthesis of DNA starting from the humble beginningsof early Earth. But even if this is done, there is no wayto tell if this was same way that DNA was originallymade on Earth. There may be a multitude of routes forreaching DNA. A very frustrating field of inquiry.

6.16 Still, humans are incurably curious

One final note on this issue. The continuing uncertaintyenveloping the question of life’s origin is a naturalconsequence of the scientific mind seeking answers todifficult questions. Despite the overwhelming magnitudeof this problem, scientists seem willing to work at it. Inthe words of physicist, Richard Feynman, “Confusion isa terrible thing.” Science provides an opportunity forskeptical people to eliminate confusion in their lives. Ifwe discover the one true origin theory, it willundoubtedly be one of the greatest accomplishments ofhumankind. But even if we don’t find it, the search willbe nothing less than a celebration of the human mind’sunending desire for understanding. And this alone isreason enough to continue.

17.17 Life and biosynthesis

Anyways, life did get started on Earth a long time ago.And it has become very sophisticated in the way itchemically exploits the planet. Today, the chemistry oflife powerfully churns the planet and leaves itsremarkable impression on the planetary surfaceenvironment. But what is the nature of life’s planet-changing chemistry? What kinds of materials is lifemoving back and forth? And to what end? I addressthese questions in the next chapter.

Trying to determine how life began onEarth is like trying to explain how afootball stadium came to be filled withpeople.

Suppose you investigate the crowd anddetermine that one of the football fanscame to the game from City A. Does thismean that all the fans came from City A?The problem is that there are dozens ofcities near the stadium. The fans in thestadium could have trickled in from all ofthem. There is no logical way todetermine from which city each personcame.

But the problem gets even morecomplicated. Suppose you identify all thefans who came from City A. What routedid they take? There could be dozens ofroutes. One person could have taken themost direct route. Another could havegotten there in a roundabout way. Forexample, she could have stopped off topick up a friend. Then they could havestopped to get some gas and beef jerky.Then they might have taken a less directroute in order to avoid traffic.

Like the fans filling up a football stadium,life could have started from manydifferent potential starting points. Andthere are dozens of different routes thatlife could have taken from each potentialorigin point.

Panel 6.1 The route of the problem