Download Plate Tectonics and Astrobiology

Plate Tectonics and Astrobiology
Life on earth evolved with plate tectonics. Would life elsewhere need it?
What does plate tectonics have to do with astrobiology?
Plate Tectonics refers to the very slow (few cm per year) movement of ‘plates’ of planetary crust
across the surface of the Earth, as well as the effects produced at the boundaries of these adjacent
plates. It is fundamentally caused by the still-cooling interior of the Earth. Escaping heat creates great
convection motions (like boiling water) in the mantle beneath the crust, which cycle material from
mantle to crust and back again, every few hundred million years. When plates contain continental
masses on the surface, their motions lead to so-called ‘continental drift’. The book Rare Earth (Ward
& Brownlee, 2000) has a good discussion.
What is the evidence of plate tectonics on a planet?
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Long, linear mountain ranges
Long linear patterns of earthquakes and volcanoes
Chains of hot spot volcanoes
Which solar system bodies have evidence of current or past plate tectonics?
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Mercury has no past or present evidence of plate motions
Venus may have had a plate tectonic system in the past
Mars may have had some plate motion in the past, but not at present
The mobile “ice rafts” on Jupiter’s moon Europa are analogous to the moving slabs of earth’s
crustal plates, but underneath the Europan ice appears to be liquid water, not a hot substance
like the semi-molten rock upon which earth’s plates move
Earth is the only body in our solar system with active plate tectonics
Effects of plate tectonics on Earth (some visible from space):
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Long, linear mountain ranges
Long, linear patterns of earthquakes and volcanoes
Chains of hot spot volcanoes
High levels of biodiversity due to the separations of continents
A ‘thermostat’ effect whereby any changes in the sun’s energy output (the sun was 30%
fainter in the past!) tend to be offset by chemical cycling controlled by plate tectonics. This
effect turns out to determine the amount of carbon dioxide in our atmosphere (via the
‘greenhouse effect’), which keeps the surface temperature in the range where most water
remains liquid, an absolute necessity for life.
Creation of continental land masses which influence:
o the amount of solar energy reflected back into space
o glaciation events (such as the Ice Ages)
o ocean circulation patterns
o global climate patterns
o nutrients reaching the sea
All of these results of plate tectonics have influenced Earth’s geo-biological history and
ecosystems for over 4 billion years, causing both increased diversification of species and
extinctions of species.