astrobiology talk

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DEFINITIONS OF LIFE

1. / 7. “matter that can reproduce itself and evolve as survival dictates”

2. “THERMODYNAMIC systems with an organized MOLECULAR structure that can reproduce itself and evolve as survival dictates”

• no good reason why it has to be chemical

• robots might outlive organisms

• don’t know chemistry at high pressure

• entropy gradients -> Jupiter-sized planets

3. biological definitions

example of respiration

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DIVERSITY OF LIFE ON EARTH

• We have very little idea about prehistoric life except for the types that have fossilised.

• Almost all species go extinct without leaving any noticeable trace at all.

• The details of large parts of the evolutionary tree of life are largely guesswork. (Although not as much as Christian fundamentalists would like us to think!)

• We haven’t studied all the environments that could support life on earth.

• We haven’t studied any environment completely - gene mush

• We haven’t studied rainforests thoroughly, although they contain the most large-animal diversity.

• We’ve barely studied the upper atmosphere.

• We’ve barely studied the oceans, except for a few commercially important parts.

• We’ve barely studied the soil, except for the top couple of hundred metres.

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prokaryotes

bdelloid rotifers

Last year, “restoration of bdelloid rotifers after being frozen for 24,000 years in the Siberian permafrost.”

Desulfurodis audaxviator

• discovered down a mineshaft in 2006

• one-organism ecosystem

• doesn’t use sunlight, even indirectly

Deinoncoccus radiodurans

Mammals are notably:

• well understood (biologically!)

• oxygen-breathing (aerobic)

• sexual

• non-parasitic

• enormous

• slow to evolve

• recent

• rare, both measured in numbers measured by weight (``biomass’’)

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Conclusions - So what can we look for?

• any kind of chemistry/atmosphere might be interesting, not just oxygen atmospheres

• lone Jupiters are at least as likely to have life as Earths in a Goldilocks zone

• SETI