Earthrise over Smythii impact basin with Schubert impact crater on horizon. Views like this during Apollo missions made it clear that Earth is part of a planetary system rather than an isolated sphere, subject to the same bombardment that battered the surface of the Moon. (Apollo 11 AS11-44-6551)

Earth, the “Third Rock from Sun” is also called the “Lonely Planet” because,

to our knowledge as yet, earth is the only

planet with evidence of life and it is water that

creates this uniqueness.

This uniqueness This uniqueness comes from two comes from two cycles that define cycles that define the Earth ...the Earth ...

hydrological cycle;

and

plate tectonics.

EvaporationEvaporation320,000 km320,000 km33

PrecipitationPrecipitation285,000 km285,000 km33

PrecipitationPrecipitation95,000 km95,000 km33

Run-off: Run-off: 35,000 35,000

kmkm33

Ocean StorageOcean Storage1,370,000,0001,370,000,000 kmkm33 Sediments

A conceptual look at the hydrological cycle. Notice its following peculiarities:1. Evaporation exceeds precipitation over the oceans,

but precipitation exceeds evaporation on land.2. Currently, atmosphere transfers by precipitation all

the water it receives by evaporation.3. Run-off carries excess water as also rock materials

from land to to oceans.

EvaporationEvaporation60,000 km60,000 km33

Hydrological Cycle and Global Warming ─ the Science of Climate Change

H and O, the two elements that comprise the water molecule, are quite common.

1012

108

104

100

10-4

0 20 40 60 Atomic Number

Ab

un

dan

ce R

elat

ive

to S

i = 1

06

Mean Distance from SunMass

DiameterLength of Day

Length of YearSurface Gravity

108.2 million km0.815 AU12,104 km243 Earth days225 Earth days0.91 AU

149.6 million km1 AU (5.974x1024 kg) 12,756 km24 hours365.2422 days1 AU

228 million km0.107 AU6,794 km24.6 Earth hours687 Earth days0.377 AU

Venus Earth Mars

Venus and Mars are Earth’s immediate neighbors and compositionally similar to the Earth.

Earth is farther from the Sun compared to Venus, and Mars is still farther.

Mean SurfaceTemperature

Mean SurfacePressure

Mean density

Major Gases

15° C60° F

1 bar

5.52 gm/cm3

77% Nitrogen21% Oxygen0.93% Argon~ 1% water (varies)

Earth

-55° C-67° F

0.007 bars

3.933 gm/cm3

95% Carbon Dioxide

2.7% Nitrogen1.6% Argon1.3% Oxygen

      Mars

457° C855° F

90 bars

5.204 gm/cm3

96% Carbon Dioxide

3.5% Nitrogen

Venus

The Atmospheres of Venus, Earth and Mars

http://www.planetary.org/saturn/atmos_compare.html

MarsThin atmosphere (almost all CO2 in ground). Average temperature: -50°C

Earth0.03% of CO2 in the atmosphere. Average temperature: 15°C

VenusThick atmospherecontains 96% CO2. Average temperature: 420°C

The whole earth is richer in Fe, Mg and Ni, and poorer in Si, K and Al, than what

is found on the earth’s surface.

Whole Earth density = 5.5 gm/cm3

Density of the crust = 2.7 gm/cm3

Outercore

Mantle

Co

re

CrustRo

ckyM

etallic Innercore

HydrogenHelium

OxygenCarbon

Nitrogen

SiliconNeon

MagnesiumIron

SulphurAluminum

CalciumNickel

SodiumArgon

ChromiumPhosphorous

ManganeseChlorine

PotassiumOther elements

HHe

OCN

SiNeMgFeSAlCaNiNaArCrPMnClK

74.50023.840

0.82000.37500.0910

0.08300.05500.05700.10400.03800.00660.00740.00920.00330.00300.00320.00090.00110.00060.0003

29.8

15.6

13.933.3

1.51.82.00.2

1.9

UniverseWholeEarth

SiO2

MgO

FeO

Al2O3

CaO

Cr2O3

Na2O

MnO

TiO2

K2O

Earth

45.1%

38.3%

7.8%

4.0%

3.5%

0.5%

0.3%

0.1%

0.2%

0.03%

Mars

44.4%

30.2%

17.9%

3.0%

2.4%

0.8%

0.5%

0.5%

0.1%

0.04%

How about water on Mars?

Mars is ... compositionally similar to Earth; and appears to have once had water.

The problem is that Mars ... lacks the atmosphere that would have

enabled it to retain water; and no longer has the plate tectonics that the

planet appears to have once had.

Mars has two moons, Phobos

and Deimos.

This image is a map of Martian magnetic fields in the southern highlands. It is where magnetic stripes

possibly resulting from crustal movement are

most prominent.

http://science.nasa.gov/newhome/headlines/ast29apr99_1.htm

Some images Some images of the Martian of the Martian

surfacesurface

Sunset on MarsAn enhanced image of a Martian sunset as seen by the Sojourner rover in 1997.

"Twin Peaks" on the horizon of the Mars

Pathfinder landing site.

Evaporation320,000 km3

Ocean Storage1,370,000,000 km3

Precipitation285,000 km3

Precipitation95,000 km3

Evaporation60,000 km3

Run-off: 35,000 km3

Without the run-off from land, ocean may eventually dry-up but that can occur only if water gets locked

up in the atmosphere. Shouldn’t that foggy atmosphere then end up lowering

the evaporation rate?

The hydrological cycle is self-destructiveThe run-off from land also erodes the rocks and deposits this eroded material in the oceans, at the rate of ~15 billion metric tons per year. As the calculations alongside show, this should take no more than ~200 Ma to fill up the ocean basins. The run-off component of the hydrological cycle should thus eliminate the hydrological cycle in ~200 Ma.

Time run-off needs to fill the ocean basins

http://www.ngdc.noaa.gov/mgg/image/sedthick9.jpg

The Wilson Cycle

Therefore, distance from Sun is not the reason why Earth has abundance of water and Venus and Mars lack water.

Solar heat received at the surface of Venus is about the same as that received on the Earth’s surface and on the surface of Mars.

Venus

Earth

Mars

0.72 AU

1.00 AU

1.52 AU

~2500 W/m2

~1360 W/m2

~ 600 W/m2

~650 W/m2

~680 W/m2

~600 W/m2

323°K

276°K

215°K

730°K

281°K

215°K

Solar heat received...... at the planetary location

... at the planetary

surface

Expected surface tempe-rature

Observed surface tempe-rature

Relative distance from Sun

Temperature profiles of the atmospheres of Venus

and Earth

Major constituents of Seawater at 3.5% SalinityConstituent

Water: Oxygen (O) Hydrogen (H)

The most abundant ions

Chloride (Cl-)

Sodium (Na+)

Sulfate (SO42-)

Magnesium (Mg2+)

Calcium (Ca2+)

Potassium (K+)

Bicarbonate (HCO3-)

85.8% 10.7%

1.9%1.1%0.3%0.1%

0.04%0.04%0.01%

only 2% of Cl in seawater could

have come from land sources

only 20% of sulfur in seawater could

have come from land sources

1,000

1

10

100

10,000Q

uad

rilli

on

(10

15)

Met

ric

To

nsEstimated existing quantity

Annual volcanic output x Age of the Earth

Water

Sulfur

Nitrogen

Carbon

Chlorine

This comparison of the total quantities of selected substances in the oceans and atmosphere with what could have come from volcanism favors the volcanic origin of these substances. Adapted from Robert Decker & Barbara Decker: VOLCANOES (W.H. Freeman, New York, 1996)

A trio of frames from Polar's Visible Imaging

System (VIS), taken 6 seconds apart on

December 31, 1998, captures an object rapidly descending

toward northern Europe. Because the

camera's filter isolates emission from hydroxyl

(OH) radicals, the incoming object must

have contained abundant water.

The case for extraterrestrial origin of oceansDeuterium

Total Hydrogen ratio

Comet HalleyEarth’s Oceans

0.06-0.48 ppt0.16 ppt

Comets are >40% water.

The deuterium/hydrogenratio of comets and oceansoverlap.

During the initial 2 Ga of its history, Earth may well havereceived 2 x 108 to 1 x 1017 metric tons of cometary matter by way of bombardment episodes.

Comets may well have contributed significantly, therefore, tothe hydrospheric mass of 1.4-1.7 x 1018 metric tons. Indeed, allthis water could have been produced by either ~10% of thecometary mass or entirely by the asteroidal source if initialbombardment was of carbonaceous chondrites.

Adapted from C.F. Chyba & C. Sagan in COMETS AND THE ORIGIN AND EVOLUTION OF LIFE(Ed: P.J. Thomas, C.F. Chyba & C.P. McKay; Springer-Verlag, New York, 1997).

Suppose

• annual influx from outer space is 50-100 billion gallons of water vapor into the atmosphere, and that Compare this to the

total amount ofwater in the oceans

= 1370x106 Km3 (volume)

109 m3/Km3

264.2 gallons/m3

= 362 1018 gallons of water

• this rate has been constant through geological history (~4.5 billion years).

This amounts to 225-450 x 1018 gallons ofwater.