What makes What makes Earth the Earth the “Blue “Blue Planet”?Planet”?

== x 100 x 100

70.9% of Earth’s 70.9% of Earth’s surfacesurface

361.8x10361.8x1066 km km22

510.1x10510.1x1066 km km22

Earth’s total Earth’s total surface surface area = 510x10area = 510x1066 kmkm22 (= 4(= 4RR22, where R , where R = Earth’s radius = = Earth’s radius = 6371 km and 6371 km and = = 3.14)3.14)

Ocean surface Ocean surface areaarea

Earth is called the Earth is called the “Blue Planet” because “Blue Planet” because water covers water covers >>70% 70% of Earth’s surfaceof Earth’s surface

Ocean surface= 361.8

x106 km2

Earth’s surface

Land surface= 148.3

x106 km2

106 510x

km2

The World Ocean

Area(106 km2)

Mean Depth(km)

Volume(106 km3)

Pacific OceanAtlantic Ocean

Indian Ocean

165.282.473.4

4.2823.9263.963

707.6323.6291.0

This view from above the North Pole showsthe Arctic Sea at the center.

When global warmingmelts the polar ice cap here, will that

hurt the polar bear or help?

Mother Polar Bear and Cubs Emerging from

Den in this BBC Planet Earth video clip.

Amazing images taken from the Arctic circle as a mother bear emerges from her winter long sleep with two new arrivals. With brilliant images of ... 1 year ago 65,462 views

This is the view of the Earth from above the South Pole. Notice Antarctica at the

center. The oceansurrounding it, the

Southern Ocean,has very high

biological pro-ductivity, thanks to the vigorous rotation-driven

circulation called West Wind Drift. Little wonder the

penguin forgot flying,making us wonder if the

Penguin is really a bird!

http://www.worldatlas.com/aatlas/imageg.htm

Equator divides the Earth into two equal halves, with North Pole at the center of one half and South Pole at the center of the other.

... and water is blue because... and water is blue because its absorption its absorption bands extend through the red part of the bands extend through the red part of the visible spectrum (red light absorbs 100 visible spectrum (red light absorbs 100 timestimes101044

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coeffi

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(cm

Ab

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coeffi

cie

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(cm

-1-1))

100 nm100 nm 1 1 μμmm 10 10 μμmm

WavelengthWavelength

more than blue more than blue light).light).

Together with the Together with the five-times greater five-times greater scattering of blue scattering of blue light over red light,light over red light, this absorption his absorption spectrum of water spectrum of water contributes to the contributes to the blue color of lake, blue color of lake, river and ocean river and ocean waters.waters.

http://www.lsbu.ac.uk/water/vibrat.html

Water is a chemical compound, Water is a chemical compound, HH22O, that …O, that …

forms from the joining of forms from the joining of one oxygen and two hydrogen one oxygen and two hydrogen atoms, i.e., atoms, i.e., 2H2H22 + O + O22 2H 2H22OO

andand

survives between 0ºC survives between 0ºC and 100ºC temperatures.and 100ºC temperatures.

We should therefore find water We should therefore find water at all the locations having at all the locations having adequate quantities of hydrogenadequate quantities of hydrogen and oxygen and 0ºC ― 100ºCand oxygen and 0ºC ― 100ºC temperatures.temperatures.

HydrogenHydrogen

OxygenOxygen

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Atomic Number (Z)Atomic Number (Z)

Click on this image to access NOVA History of the Universe

Judging from chemistry, Judging from chemistry, water should abound all water should abound all

over the universe.over the universe.HydrogenHydrogen

HeliumHelium

OxygenOxygenCarbonCarbon

NitrogenNitrogen

SiliconSiliconNeonNeon

MagnesiumMagnesiumIronIron

SulphurSulphurAluminumAluminum

CalciumCalciumNickelNickel

SodiumSodiumArgonArgon

ChromiumChromiumPhosphorousPhosphorous

ManganeseManganeseChlorineChlorine

PotassiumPotassium

HHHeHe

OOCCNN

SiSiNeNeMgMgFeFeSSAlAlCaCaNiNiNaNaArArCrCrPPMnMnClClKK

74.50074.50023.84023.840

0.82000.82000.37500.37500.09100.0910

0.08300.08300.05500.05500.05700.05700.10400.10400.03800.03800.00660.00660.00740.00740.00920.00920.00330.00330.00300.00300.00320.00320.00090.00090.00110.00110.00060.00060.00030.0003

Composition of the UniverseComposition of the Universe

0.1 1 10

2

1

0.5

Mas

s of

the

sta

r, r

elat

ive

to S

un

Radius of planetary orbit, relative to Earth

Ear

th

Ven

us

Mer

cury

Mar

s

Jupi

ter

Sat

urn

Ura

nus

Nep

tune

Habitable zone

20

Using the concept of black body radiation, we can compute if the planetary surface is hot enough for water to exist, because a black body emits away all the incident radiation that it receives, i.e.,

Total Incident Power (Pincident) = Total Outgoing Power (Pemitted)

Now, Pincident = (1–α)LπR²

for a planetary disc of radius R, where L is incident radiation and α is albedo, the proportion of heat that is reflected away (i.e., α = 0 when the entire incident radiation is absorbed and α = 1 when the entire incident radiation is reflected away. As the heat emitted by the planet is over its entire surface, Pemitted = 4σT4πR² where σ =

5.67x 10-8W/m2K4 is the Stefan-Boltzmann cons-tant and T is the planetary surface temperature in Kelvin. For Pincident = Pemitted and α = 0, we then have L = 4σT4. This yieldsL = 1260W/m2 for T = 273K (0°C) to L = 4390W/m2 for T = 373K (100°C). This region is called “habitable zone”.

This stunning picture of sunset at the North Pole was taken in August 2009

EvaporationEvaporation320,000 km320,000 km33

EvaporationEvaporation60,000 km60,000 km33

Ocean storage1,370,000,000 km3

Precipitation285,000 km3

Precipitation95,000 km3

Run-off: 35,000 km3

http://www.youtube.com/watch?v=qyb4qz19hEk&feature=related NASA | Earth Science Week: Water, Water Everywhere!6:32

A conceptual look at the hydro-logical cycle. Notice three aspects of it:

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 the oceans.

Run-off also erodes rock materials from land and piles them as sediments on the

continental margins

Two Questions

1. How and why does atmosphere return all the evaporated water back to the Earth?

2. Does run-off only take the land’s excess (i.e., P-E) water to the ocean or carries something additional?

As for the first question, troposphere’s temperature gradient forces the return of evaporated waters back to the Earth.

Pressu

reW

eather zone

Alt

itu

de

Wilson Cycle ― which ensures the continuous reshaping of Earth’s surface geography, such that new ocean basins are created where we once had

land and the new surface area thus created isbalanced by an equal surface area in the mountain belts and deep sea trenches ― answers the second question.

Mount Annapoorna, 26,545 ft (8,091 m)

This Himalayan peak, Mount Annapoorna, is made up of limestones with ~200 Ma old ammonite fossils, suggesting that an ocean once existed where we now have the world's tallest mountains!

Clearly, an ocean existed at this location ~250 Ma ago, when these limestones formed.

~250 Ma old Kaibab limestones form the floor

of the Kaibab National

Forest where the

Grand Canyon National Park

is located.

http://www2.nature.nps.gov/geology/usgsnps/animate/A08.gif

This animation of Alfred Wegner’s PANGEA, a supercontinent that

existed ~250 Ma ago, shows how Atlantic andIndian

oceans formed from

PANGEA’s dispersal, a

process that also created

the Himalayas, Andes and

Alps.

New ocean floor is created by spreading about the

mid-ocean ridge, the

site of incessant

basalt volcanism

The new surface area created by sea-floor spread is compen-sated by loss of equal surface area at the

Folded Mountain Belts (above) and Deep Sea Trenches (left)

http://www.omnimap.com/catalog/int/worldmps.htm

As this map shows, the relative youth of ocean As this map shows, the relative youth of ocean floor is a peculiarity of the world geological map.floor is a peculiarity of the world geological map.

00 55 6565 135135 185185 6565

The older sea The older sea floor tends to floor tends to

be farther be farther from the from the

ridge axisridge axis

0.0

0.0

9.6

9.6

20.2

20.2

33.0

33.0

40.2

40.2

47.9

47.9

56.0

56.0

68.7

68.7

83.0

83.0

118

.011

8.0

126

.512

6.5

131

.713

1.7

141

.914

1.9

149

.914

9.9

156

.615

6.6

180

.018

0.0

Age of the sea floor (Ma BP)Age of the sea floor (Ma BP)

http://www2.nature.nps.gov/geology/usgsnps/animate/A55.gif

http://www2.nature.nps.gov/geology/usgsnps/animate/A08.gif

This animation of Alfred Wegner’s PANGEA, a supercontinent that

existed ~250 Ma ago, shows how Atlantic andIndian

oceans formed from

PANGEA’s dispersal, a

process that also created

the Himalayas, Andes and

Alps.

The spreading seafloor records the The spreading seafloor records the geomagnetic polarity reversals that geomagnetic polarity reversals that occur as the basaltic seafloor forms.occur as the basaltic seafloor forms.

H

OH

2H2

+O2

2H2O

2H2H22 + O + O2 2 2H 2H22OO

HOO

H

OOH

H

HOO

H

HOO

H

Water is a chemical Water is a chemical compound that forms from compound that forms from

the joining of one oxygen the joining of one oxygen andand

two hydrogentwo hydrogen atoms, i.e.,atoms, i.e.,

2H2H22 + O + O22 2H 2H22OO

HydrogenHydrogenOxygenOxygen

Bulleted cartoonsBulleted cartoonsLet us look atLet us look at

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Atomic Number (Z)Atomic Number (Z)

HydrogenHydrogenHeliumHelium

OxygenOxygenCarbonCarbon

NitrogenNitrogen

SiliconSiliconNeonNeon

MagnesiumMagnesiumIronIron

SulphurSulphurAluminumAluminum

CalciumCalciumNickelNickel

SodiumSodiumArgonArgon

ChromiumChromiumPhosphorousPhosphorous

ManganeseManganeseChlorineChlorine

PotassiumPotassiumOther elementsOther elements

HHHeHe

OOCCNN

SiSiNeNeMgMgFeFeSSAlAlCaCaNiNiNaNaArArCrCrPPMnMnClClKK

EarthEarth

29.829.8

15.615.6

13.913.933.333.3

1.51.51.81.82.02.00.20.2

1.91.9

74.50074.50023.84023.840

0.82000.82000.37500.37500.09100.0910

0.08300.08300.05500.05500.05700.05700.10400.10400.03800.03800.00660.00660.00740.00740.00920.00920.00330.00330.00300.00300.00320.00320.00090.00090.00110.00110.00060.00060.00030.0003

UniverseUniverse

Note that chemistry is not the Note that chemistry is not the reason why water shouldreason why water should

occur all over theoccur all over the universe.universe.

OEC

A

7N

(%8

0.)

L

(

AN

D

%29.2

)

Oceanridges(22.1%)Continental

platforms(18.9%)

Oceanbasin floors(29.8%)

Continental shelf and slope (11.4%)

Island arcs, trenches, guyots etc. (3.7%)

Continental rise (3.8%)

Conti-nentalmountains(10.3%)

Click on this image links to access the NOVA History of the Universe