GEOLOGIC TIME, WATER,& EARTH CROSS SECTION

GEOL 1033

GEOLOGIC TIME - Earth is 4.65 Ga old• A diagrammatic

representation of the last 4.0 billion years of the geological time scale of the Earth showing the different groups of organisms that evolved through time. Note that man's presence on earth represents just an extremely small fraction of the 3.5 billion year history of life on Earth. On a 24 hour clock, our species, Homo sapiens, appeared at 2 seconds before midnight.

• Oceans probably existed at about 4 Ga

• Life began in the oceans

GEOLOGIC TIME SCALE

• Geologic time terms:

Eon

Era

Period

Epoch

Age

• Two major divisions:– Precambrian

(4.7 Ga - 544 Ma)

– Phanerozoic

(since 544 Ma)

• Ma = million years

• Ga = billion years Hadean

GEOLOGIC TIME SCALE• Be aware of the

Geologic Time Scale in general.

• What is the Carboniferous Period?

• What is the Jurassic Period?

• When did it begin? • Why is it important

to oceanography?• What is the

Pleistocene Epoch?• When did it begin

and end?• Why is it important

to oceanography? 4.65

Hadean

WATER DISTRIBUTION ON EARTH'S SURFACE

• The Pacific Ocean is by far the largest ocean.

• "Antarctic Ocean" is really part of the Pacific, Indian, & Atlantic oceans

• Arctic Ocean is the smallest.

• Antarctic and Greenland ice caps have 1.5% of Earth's surface water.

• Lakes, rivers, & atmosphere have only <0.1% of water!

Where is the Arctic Ocean?

?

HEMISPHERIC DISTRIBUTION OF LAND

• 71% of Earth's surface is covered by the oceans.

• A northern land hemisphere

• A southern water or ocean

hemisphere

WATER DISTRIBUTION ON EARTH'S SURFACE• ~98% of Earth's surface & near-surface water is in the

oceans as liquid or floating sea ice• Frozen seawater:

• Excludes salts

• Leaves a cold brine as a residue

• Forms freshwater when it melts

• ~97% of Earth's surface & near-surface water is saline.

SOME CHARACTERISTICS OF THE WORLD’S OCEAN

• Oceanic water covers a surface area of

about 361 100 000 km2 or 3.611 x 108 km2

• Oceanic water volume equals about 1.37 x 109 km3

• Average depth of the oceans is about 3.8 km (~12,450').

• Average temperature of the oceans is about 4 deg. C.

• Average salinity is about 34.482 o/oo (=34.482 g/kg) or about 3.5%

HYPSOMETRIC CURVE

Cumulative area of Earth's surface above a certain depth or elevation, e. g., 29% is above sea level & 71% is below sea level.

2 major elevations:– near sea level

– deep ocean floor

29%

71%

TILT OF EARTH'S ROTATIONAL AXIS

• 23.5 degree tilt of Earth's rotational axis exerts a controlling influence on climates, ocean circulation, etc.

Earthquake P & S Body Waves

• Review earthquake wave propagation before studying a cross section of Earth

•Compare the hammer/board, spring, & rope models of P and S waves

CROSS SECTIONS OF EARTH• Study of seismic waves from earthquakes indicate

– Core with 2 layers• inner solid• outer liquid

– Mantle with many layers• lower lithosphere• asthenosphere• mesosphere

– Crust with 2 types• continental• oceanic

• Lithosphere includes:– Crust

– Upper mantle

CROSS SECTIONS OF EARTH• Core (2 layers)

• Mantle (3 layers)• Crust (2 types)

Outer core is all liquid

Fe,Mg

Si, NA, K

Silica Models

CROSS SECTIONS OF EARTH

Lithospheric layers:– Crust (oceanic or continental)– Uppermost mantle

OCEAN-CONTINENTAL MARGIN CROSS SECTION DOWN TO THE MESOSPHERE

Ast

heno

sphe

re

OVERVIEW OF PLATE TECTONIC PROCESSES

Thermal Convection

TABLE SUMMARIZING EARTH CROSS-SECTION DATAName of Layer Radius (km) Density State of Rock Name or

(g/cm2) Matter Composition

CRUST:

Continental up to 60 2.7 solid Granitic

(more silica, SiO2)

Oceanic 5-10 2.9 solid Basaltic

(less silica, SiO2)

MANTLE

Lithosphere ~100 ~3.1 solid Iron- & magnesium-

Asthenosphere ~600 ~3.3 solid rich silicates

Mesosphere ~2,200 ~4.5-8 solid

CORE:

Outer 2,200 ~8 liquid Mostly Fe with some

Inner 1,300 >10 solid Ni, S, & Si

ELEMENT ABUNDANCE IN THE CRUST and WHOLE EARTH• Abundance of elements in the crust by percentage weight:

– Oxygen O 47%

– Silicon Si 28

– Aluminum Al 8

– Iron Fe 5

– Calcium Ca 3.6

– Sodium Na 3

– Potassium K 2.6

– Magnesium Mg 2

– all others 1.5

• Whole Earth order of abundance:– Iron Fe 35%

– Oxygen O 30

– Silicon Si 15

– Magnesium Mg 13

– Nickel Ni 2.4

– Sulfur S 2

– Calcium Ca 1

– Aluminum Al 1

– all others (incl. Na, K) <1

PERIODIC TABLE of the ELEMENTS

END OF FILE

Review Questions:

• What are the two most abundant elements in the crust?

________________ ________________

• What is the depth of the deepest earthquake? _______________

• Magma is rising from deep in the mantle beneath

mid-ocean ridges where seafloor __________________ occurs.

• Thermal convection in the ______________ may be the driving mechanism for plate tectonics.

• The proto-Atlantic ocean basin began to form about

__________ Ma ago near the beginning of the Jurassic Period.

• The average salinity of seawater is _________________ o/oo

• The ___________ Ocean is the largest ocean on Earth.