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.

Re:Occam's Razor

[pigeon768]

Occam's Razor is not a "theory" in any sense of the word. It cannot and will not ever be proved. Physicists use it so much as a "divining rod" simply because of the fact that in so many cases, it's correct. IOW if they know that the answer they're looking for is one of 2 equations, they'll test the simpler one first.

Gravity is described as f = m(1)m(2)G/r^2. Einstein's theory of relativity is described as E = mc^2. F=ma, D = 1/2at^2 + vt + d(0), PV = nRT etc. etc... All seemingly complicated things described by very simple formulas. The vast majority of phenomena in physics are described by relatively simple equations. (major exceptions being any form of turbulence or a result of turbulence)

Then again, Occam's Razor doesn't apply very well to life sciences, which is what this is about.

Two Points

[Entropix]

First, I noticed some discussion as to Quantum Physics being far more complicated than Classical Physics, so Occum's Razor doesn't really apply -- well, actually it might not be. It turns out there are many relationships that exist between current string theories and 11-dimensional supergravity, suggesting that these various theories (Heterotic 0, Heterotic E, I, IIA, IIB) are all expressions of the same thing. Perhaps a single M-theory exists that can describe our universe. Second, I'd like to mention that this talk about FTL travel is futile. Besides the problems with mass and energy and time slowing, there are plenty of other options that actual physicists such as Stephen Hawking (i.e. not ones holding up a lightbulb they call "The Doom Machine") have discussed. For example, there is the bending of space-time fabric to move quickly from one point to another. There is even the possibility of so-called wormholes or Einstein-Rosen bridges being constructed and prevented from being closed by a negative energy force such as that is present in the Casimir effect. Of course, this is predominantly theoretical, and at least a couple hundred years off in this author's humble opinion. Oh, and anyone interested in Drake's Equation (a.k.a. the Sagan equation), you can try Eric Weisstein's World of Physics at: http://scienceworld.wolfram.com/astronomy/DrakeEqu ation.html [scienceworld.wolfram.com] - Entropix

Re:1 != Many

[AJWM]

Good points about Venus and Mars which orbit at the edges of the "life zone".

One possibly critical datum missing from that analysis relates to Earth's history. Earth has a relatively thin crust and the combination of tectonic motion, subduction, and vulcanism recycles elements back to the atmosphere after they'd been locked up in rocks. (Actually you do hint at this in your last para.)

Mars seems to be small enough that it has solidified down far enough that there's no more cycling of the crust and thus the oxygen and hydrogen locked in the rocks stays there, also any free hydrogen (from the ultraviolet lysis of water) escapes to space before it can recombine, thus Mars now has a very thin atmosphere.

Venus may be large enough, although that isn't certain. It certainly seems to have continental masses but I don't know about any active volcanism. It's heavy enough to retain atmosphere though -- too much of it, as you point out.

It's possible that the reason Earth escaped Venus's fate has less to do with the distance from the Sun and more to do with the formation of our Moon. Current theory is that late in the formation of the solar system, the proto-earth was smacked by a Mars-size protoplanet which literally splashed a good chunk of the proto-Earth into space, some of which condensed to form the Moon. This has several implications. The lightest elements would have boiled away in significant quantity, so there's just less of them around to form a thick atmosphere (hence less runaway greenhouse). The medium light-weight elements (that form crust, particularly continental crust) were greatly reduced, some of them forming the Moon (so in one sense, the Moon is the 8th continent), meaning that tectonic circulation has an easier time of it. (The heat from that impact might also have some effect there, although I think that would be dissipated by now.)

All of which leads to the (somewhat depressing) conclusion that Earth is habitable only because of a really unlikely sequence of events (much more unlikely than merely forming at the right size in the right place). OTOH, observation of our own solar system and some of the very strange (to us) places on Earth that life survives and thrives indicate that there could be a lot of places that primitive life exists. Star Trek's "Class M" planets are probably pretty darned rare, though.

(Oh, BTW, Mercury isn't in "tidal lock" like the Moon is with Earth, but in a 3:2 tidal resonance with the Sun.)