For my #nerdy9th
entry (first and/or only as may be), I'm going to talk about someone who brings together two of my loves, natural history and good writing: paleontologist Peter D. Ward.
I discovered Ward via the first of his collaborations with astronomer Donald Brownlee, Rare Earth: Why Complex Life is Uncommon in the Universe
. It isn't just complex life that's rare in their argument, it's the stance they took...okay, that's reaching too hard for the joke.
Traditionally, views about life beyond earth have fallen toward two poles: either life of any kind at all is very rare, or life of all degrees of complexity is quite common. I grew up with the argument over extraterrestrial life pretty much going that way - a dead universe, or a universe loaded with biomes as rich as our own.
Discoveries made about life on Earth made the latter look more likely: the whole ecosystems that flourish around deep-sea volcanic vents, the communities that gather around briny seeps, also on the sea floor, extremophile bacteria happily hanging out miles below the earth in high heat and pressure, in waters laden with chemical goop that kills everything conventional in the area, in high-radiation conditions, you name it. It became clear, piece by piece, that life appeared very nearly as soon as it possibly could on the early Earth and that it will go everyplace it can, including places you wouldn't have though it could.
Astronomical studies make a lot of use of the mediocrity principle, the idea that we (and what you're studying) is presumptively not freakishly weird or unusual until you can establish otherwise. It's a handy guide, as you look at new phenomena nobody ever expected to see, because it it feeds directly into new goals for study (hey, is this going on anywhere else now that we know to look for it?) and checking your data for possible sources of contamination (wait a sec, is this spike here the result of my spreadsheet doing something wonky?)
Applied to the info about life's flexibility and durability, it became easy and sensible to imagine bacterial life on places like Mars, Europa, and Titan, let alone a world that might be more Earthlike in its hospitality. And from there, the principle of mediocrity suggests, we can and should imagine the processes that shaped life on Earth giving rise to comparably complex systems just about everywhere.
This is where a complicating factor comes in, though.
Ward's specialty is mass extinctions, and particularly the Permian-Triassic one. If you're like me, and I know I am, if you know anything about any mass extinction, you're likely to know about the K-T (Cretaceous-Tertiary ("K" because it was formally titled in German)) one, in which the dinosaurs got ganked. But it turns out it's the exception to the norm for mass extinctions. The others all happened over extended periods of time, and all turn out to involve layered climate changes.
The Permian one, for instance, seems to have involve millennia of catastrophically intense volcanic activity and mass discharge of methane deposits on the sea floor and several other things combining to produce overheating and acidic rain and depletion of seawater oxygen and...it's messy. So are the others. It's that impacts can't
mess things up globally rather than locally, it's just that only one seems to have actually done so. More commonly, existing stuff on Earth runs amok.
The more we learn about the consequences of mass extinction events, the more fragile the whole history of life looks. The principle of mediocrity is hard to apply when you repeatedly destroy almost every participant, selecting mostly at random. Everything gets intensely contingent. Re-run things two or ten or a thousand times and you will, it seems, get wildly different outcomes every time.
The other thing that emerges is that there don't seem to be any brakes that can tell a mass extinction in progress, "OK, wait, enough, leave at least some." Restrain the forces contributing to a particular extinction some and it's...well, it's not quite a mass extinction, it's "just" a really hideous bunch of damage to the biosphere. Let them go a little bit more and you get a dead planet, or one that has to start over from bacteria. There are some feedback loops, but there are positive ones as well as negative, so that on the edge it can be a matter of flip...flop...flip...flop...flip flip...flop...flip flip flip flip bam
All of which is to say that there turn out to be a whole lot of ways to break a biosphere, and the more complex and specialized any particular participant is, the more trouble it's going to be in.
So the argument from people like Ward is that we may expect to find a universe filled with very simple life, but very little at anything like our level of complexity. Every world will have a tangled, complex history, and most will have an element in it of "...and then things got pushed too far, and all the complex life perished, and it hasn't yet reemerged."
Ward has written several books I highly recommend. Besides Rare Earth
, he's done a bunch on his own about extinction events. They fold together insightful, wise writing about his and others' experiences in the field and lab, about the social operations of the life sciences, and about what they discover and interpret. Gorgon
centers on the gorgonopsids, who best survived the Permian-Triassic extinction. Under a Green Sky
goes into a lot more detail about recovering the tangled history of the Permian-Triassic extinction, and ties it into how scientists interpret global warming now, and more. But there's none of his work I would not want to hold out and say "Hey, if you're at all interest in this subject, read this!"http://en.wikipedia.org/wiki/Peter_Ward_(paleontologist)