What makes the Earth habitable

1
What makes the Earth habitable?

• Water supply
• Surface temperature
• Oxygen gas
• Energy reserves

2
Water

• Water is the main ingredient needed for life
• Planet must have captured enough water to make
  oceans
• Water must have migrated to the Earths surface
• Water must not have been lost to space
• Temperature needs to be above freezing and below
  boiling

Earth is 1.5 weight percent water (captured 1 in
3,000,000 H from 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
Earth
Present day atmosphere has less 129Xe than
present day basalts
Atmosphere was formed very early on at the same
time as core formation
3
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
Where is the water?
We know how much 4He is produced over Earths
history
4
Composition of the atmosphere
5
Planet temperature

• Planet surface temperature dependent on
• Luminosity of the star it is orbiting
• Planets 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

6
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.

7
Absorption of outgoing light
Molecules made of three or more atoms are able to
absorp outgoing infrared light
Water Carbon dioxide Methane Nitrous oxide
8
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

9
Atmospheric heat balance
Earths albedo (31) is energy reflected by
clouds (22) and Earths surface (9). The
remaining incoming solar radiation is absorbed 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
Hot air, moisture and radiation export more
energy than is received. Greenhouse gases
reflect most back
10
Earths thermostat
CaSiO32CO22H2O? Ca22HCO3-H4SiO4
11
Carbon cycle
Inflow into each reservoir is balanced by
outflow Rocks contain 12 million Gt of carbon, by
far the largest reservoir
12
Earths orbit
Determines how much and where sunlight is received
13
Orbit and ice ages
Tilt, eccentricity and precession combine to
cause variations in the amount of sunlight
received by Earth.
14
Orbit and ice ages

• How 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.

15
Oxygen isotope evidence

• Ratios of two oxygen isotopes 16O and 18O
• Lighter isotope has slightly higher vibrational
  frequency and velocity
• Lighter isotope better able to go into the vapor
  phase
• Water in the atmosphere has higher 16O/18O than
  the ocean
• Precipitation out of the atmosphere will thus
  have higher 16O/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 the seawater.

16
Oxygen isotope record
Oxygen isotope record of foraminefera
Glacial less 16O in the ocean
17
Vostok Ice core
1. 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
18
During the ice age
August 16,000BC
Ice thickness in meters
Air temperatures
Sealevel was 85 meters lower than present
19
Human CO2 production

• Human activity increase the CO2 flux to the
  atmosphere by 7.1 Gt/year
• In response, new plant growth and ocean take up
  3.8Gt/year
• Result atmospheric increase of 3.3Gt/year

20
Carbon cycle
Inflow into each reservoir is balanced by
outflow Rocks contain 12 million Gt of carbon, by
far the largest reservoir
21
The record
Recent warming trends correlate with increase in
CO2 from emissions since the Industrial
Revolution of the 19th century
The 20thy century record is clearly anomalous
when compared with climate change documented
during the last millenium
22
Science, Oct 21st, 2005
23
What are the consequences?
Rate of carbon dioxide increase depends on growth
in fossil fuel use.

• melting of the ice caps
• sea level will rise 65m (200ft)
• most population centers would be flooded

Shading indicates uncertainty in the climate
models
24
Sealevel rise predictions
Prediction based on 2001 IPCC
If the Greenland Icesheet disappears
25
Sealevel for the Northeast
26
Sea level for several areas
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28
Conveyor belt
Thermohaline circulation
Salinity
Temperature
29
El Niño I
El Niño originally recognized by fisherman off
the coast of South America as the appearance of
unusually warm water in the Pacific ocean around
Christmas. El Niño means The Little Boy or Christ
child in Spanish.
The opposite La Niña means The Little Girl. La
Niña is sometimes called El Viejo, anti-El Niño,
or simply "a cold event" or "a cold episode".
30
Suwannee River
Periodicity in streamflow data for Suwanee River.
El Niño years are associated with less rainfall
and resulting less river runoff in Florida
31
El Niño II

• Normal years warm surface waters east off
  Indonesia cause low pressure and heavy rainfall
• Pressure pattern drives trade winds from east to
  west, pushing warm water westward
• 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 eastern
Pacific causes heavy rains and inhibits the cold
upwelling. 7. La Niña opposite SST.
32
Snowball Earth?