why earth is habitable.ppt

7/27/2019 why earth is habitable.ppt

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What makes the Earth habitable?

Water supply

Surface temperature

Oxygen gas

Energy reserves


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WaterWater is the main ingredient needed for life:

1) Planet must have captured enough water to make oceans2) Water must have migrated to the Earths surface

3) Water must not have been lost to space

4) Temperature needs to be above freezing and below boiling

Earth is 1.5 weight percent water (captured 1 in 3,000,000 Hfrom the solar nebula).

When was the atmosphere formed?

129I decays to 129Xe half-life of 16Ma

Xe escapes to the atmosphere, Iodine stays in the solid EarthPresent day atmosphere has less 129Xe than present day

basalts

Atmosphere was formed very early on at the same

time as core formation


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Why did it stay?Escape depends strongly on the gravity of the planet

For Earth the speed of a molecule needs to be 11km/sec

Mean time to escape from Earth:4He 106 years; 20Ne 1011 years

We know how much 4He is

produced over Earths history

Where is the water?


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Composition of the atmosphere


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Planet temperature

Planet surface temperature dependent on:

Luminosity of the star it is orbitingPlanets distance from this star

Reflectivity of the planet

For Earth several other factors important:

Changes in the rate and pattern of mantle flow (tectonics)

Planet architecture: equatorial bulge and tilted rotational axis

results in precession

Gravitational forces (other planets) results in orbital tilt and

shape


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Earth as a black body?Black body: all light is absorbed none is reflected, but re-irradiated as light

The hotter the black body the more energy its emits

Reflectivity is important

on Earth and

- cloud cover,- ice caps, and

- deserts

reflect, and less sun

energy is absorbed.


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Absorption of outgoing light

Molecules madeof three or more

atoms are able to

absorp outgoing

infrared light

Water

Carbon dioxide

MethaneNitrous oxide


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Surface temperature

Only 60ppm of the Earths carbon budget is in the atmosphere

If all carbon was in the atmosphere as CO2 the atmospheric pressure would be 100

times higher

Venus similar to Earth in size but its CO2 is the atmosphere

Extreme greenhouse effects exists on Venus and it has lost all its water


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Atmospheric heat balance

Hot air, moisture and

radiation export more

energy than is received.

Greenhouse gases reflect

most back

Earths albedo (31%) is energy reflected by

clouds (22%) and Earths surface (9%). The

remaining incoming solar radiation is abosrbed

by the atmosphere (20%) and the Earths surface

To achieve radiation balance, Earth

radiation balance, Earth radiates the

sum of the radiation absorbed by the

atmosphere and surface back into space


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Earths thermostat

CaSiO3+2CO2+2H2O

Ca2++2HCO3-+H4SiO4


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Carbon cycle

Inflow into each reservoir is balanced by outflow

Rocks contain 12 million Gt of carbon, by far the largest reservoir


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Earths orbit

Determines how much and where sunlight is

received


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Orbit and ice ages

Tilt, eccentricity and

precession combine to

cause variations in the

amount of sunlightreceived by Earth.


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Orbit and ice agesHow can we determine there were

previous ice ages:-Continental sediment record:

recognition and dating of glacial

sediment on land

-Oceanic sediment record: rock

released by icebergs

-Ocean surface temperature recorded

by fossils

-Ice volume changes recorded in the

oxygen isotope record of fossils.


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Oxygen isotope evidence

Ratios of two oxygen isotopes: 16O and 18O

Lighter isotope has slightly higher vibrational frequency andvelocity

Lighter isotope better able to go into the vapor phase

Water in the atmosphere has higher16O/18O than the ocean

Precipitation out of the atmosphere will thus have higher16O/18O (lighter) than the ocean

Ice caps result in storage of this lighter water

Increase in ice caps makes water in the ocean heavier because

of snow and ice build up in ice caps

Marine organisms record the oxygen isotope composition of theseawater.

O i t d


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Oxygen isotope record

Oxygen isotope record of foraminefera

Glacial: less 16O in the ocean

1 Th i d li i t t


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Vostok Ice core1. There is a decline in temperature

and greenhouse gases during the

onset of glacial periods

2. Rapid rise

during

deglaciation

3. Climate has been

relatively warm during

the last 10,000 years-

the Holocene

interglacial


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During the ice age

Ice thickness in meters

Air temperatures

August 16,000BC


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Human CO2 production

1. Human activity increase the CO2 flux to the atmosphere by 7.1 Gt/year

2. In response, new plant growth and ocean take up 3.8Gt/year

3. Result atmospheric increase of 3.3Gt/year


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The recordRecent warming trends correlate with

increase in CO2 from emissions since the

Industrial Revolution of the 19th century

The 20thy century record is clearlyanomalous when compared with

climate change documented during the

last millenium


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What are the consequences?

Rate of carbon dioxide increase

depends on growth in fossil fuel

use.

Shading indicates uncertainty in

the climate models


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Conveyor beltThermohaline circulation

Temperature Salinity


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El Nio IEl Nio: originally recognized by fisherman off the

coast of South America as the appearance of

unusually warm water in the Pacific ocean around

Christmas. El Nio means The Little Boy or Christchild in Spanish.

The opposite: La Nia means The Little Girl. La

Nia is sometimes called El Viejo, anti-El Nio, or

simply "a cold event" or "a cold episode".


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Suwannee River

Periodicity in streamflow data

for Suwanee River. El Nio

years are associated with less

rainfall and resulting less riverrunoff in Florida


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El Nio II

1. Normal years warm surface waters east off Indonesia cause low pressure and heavy rainfall

2. Pressure pattern drives trade winds from east to west, pushing warm water westward

3. Cold water upwells along South America

4. Periodically air pressure

rises over the western pacific

weakening the trade winds

and warm water shifts east

5. The western pacific

experiences drought

6. Low pressure over easternPacific causes heavy rains and

inhibits the cold upwelling.

7. La Nia opposite SST.


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Snowball Earth?

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why earth is habitable.ppt