Drake on Drake: ET Life A Certainty

astro writes "Frank Drake, Chairman of the Board of Trustees of the SETI Institute applies Occam's Razor to his own Drake equation: 'Life should appear very frequently on other Earth-like planets. There will be microbial life nearby the solar system.' The simplest scenario is that 'Not Life' has a nearly identical number of assumptions as 'Life.' The contrasting view is that experimentation can prove it--but how many times did life independently create itself while the Earth changed through the whole spectrum of what biological forces might conjure up elsewhere. A sample size of 1 is in fact an experimental sample size of many--just here during Earth's climatic history."

Comments

Timing

[Michael Woodhams]

We have a sample size of only one, and that this sample resulted in intelligent life is a given (else we wouldn't be here to make observations on it.) We do however have some timing information. From this we see:

1) Life evolved on Earth pretty much as soon as conditions were stable enough to allow it. This suggests that bacterial life is highly likely.

2) It took at least hundreds of millions of years to develop Eukariotic life (big cells with a nucleus, such as we are made of, as opposed to bacteria.) This means that this step might be rare.

3) It took about 3 billion years to evolve differentiated multicellular life. This means that this step could be exceedingly rare.

4) Multicellular life evolved into a vast array of designs in a just a few million years (the 'Cambrian explosion'.) This means that once multicellular life starts, it will quickly produce complex forms.

5) From the Cambrian explosion to us is something like 500 million years. This is an intermediate time scale that makes it hard to judge how likely intelligent life is.

Disclaimer: I'm not 100% sure of some of the timescales above. It is all from memory.

Disclaimer 2: The Edicara fauna complicate the picture above on the origin of multicellular life, depending on how you interpret them.

Disclaimer 3: All the above is merely probabilistic. E.g. if the evolution of bacterial life is very rare, there is still a 5% chance that it will have occurred during the first 5% of the available time. Therefore we can't strongly exclude the possiblity that the evolution of bacterial life is hard.