How long does it take advanced life-forms to evolve?

[cthulu2016]

Last edited Fri Apr 25, 2014, 07:34 PM - Edit history (1)

That very much depends. (Advanced life-forms doesn't mean people, though we are a notable example. Multi-cellular. Cows and grass are both considered pretty advanced compared to a single-cell organism.)

On our planet we got life very early on. It was all bacteria. Single cell organisms. And it stayed single cell organisms for BILLIONS of years.

Bacteria, bacteria, bacteria...

Then about 650 million years ago evolution exploded. In the geological blink of an eye we had all sorts of multi-cellular critters and plants, some of them pretty big.

Why? because the oxygen concentration in our atmosphere went from about 1% to about 20%. Oxygen is key to metabolism. Suddenly there was a power source to build advanced forms on.

(The oxygen came from a global tragedy, which was a total ice age—glaciers meeting at the equator—for 25 million years. This was caused by a shortage of CO2. The one big land mass found its way to the equator and the heat there led to fixing CO2 in the formation of limestone. Then, during the freeze, cosmic rays kept turning stray water molecules in the ice into Hydrogen Peroxide. But since everything was frozen it stayed in place. Then a giant volcano blew a bunch of CO2 into the air starting a process of melting the ice, and all the Hydrogen Peroxide was free and broke down in the oceans releasing lots of O2. Was that O2 all being hoarded by bacteria before the freeze? I guess so. Fortunately, our advanced life forms are mostly plants who do not hoard oxygen, but rather hoard carbon to make cellulose. Anyways...)

So we have a planet just crawling with life. Then BAM, an incredible mass extinction. Then a hundred or two million years later, BAM... a mass extinction. Dinosaurs everywhere... BAM. Comet hits. Mass extinction.

The dominant life-forms after each mass-extinction tended to be more advanced, but that doesn't mean that only mass extinction catastrophes can give more advanced critters an edge. Since this planet blows the hell up so often we may never know.

Would dinosaurs have developed higher metabolism (like mammals) and eventually gotten into some arbitrary cycle where having a big brain was necessary to whatever critters used to pick who to have sex with (that's what happened to make us so smart)?

Until some sentient lizard people contact us, we probably won't know for sure.

But anyway, here is what I think...

In an environment with lots of oxygen and solar energy and a good run of luck (only the right sort and right timing of environmental catastrophes) intelligent life could arise very quickly. 100s of millions of years, but that's quick. (Though it might tend to not develop at all. We don't know how freakish our one example is.)

Now, here is a counter argument. First, if you need bacteria to "terra-form" a world, that will take a while. So if bacteria are needed to produce a useful atmosphere that takes however long it takes, and is as much an engineering question as an evolution question. So we have that starting time requirement.

Also, it is very, very, very difficult to evolve the ability to process chemicals. Chemical processing is a specialist task developed by individual species of bacterium working one problem. "Here is a substance that's around. Is there a way to eat it?" Most of our chemical processing is done by co-opting bacteria that perform some chemical task.

We use bacteria like modules. A lot of structures in our cells were captured bacteria whose DNA got spliced in as a formula for doing some chemical process. And, of course, we use bacteria directly to digest food we cannot breakdown with our cells. (Gut bacteria) Termites cannot digest wood. Bacteria do it for them. And plants didn't develop photosynthesis. The incorporated it, as a module, from algae. (Is a tree merely algae's way of getting closer to the sun? It can be argued...)

So it may take a lot of time to develop the bacterial toolbox that advanced life-forms use to be so evolutionarily flexible.

But, on the other hand... remember that 25 million year freeze that led to the explosion of multi-cellular life? That freeze killed off almost all the existing bacteria. The only life that survived was whatever could live in a world completely covered with ice.

So the question is whether it took billions of years to get to the traits those few bacterial survivors had, because they are all that future evolution had access to, after the big freeze.

On balance, I think it can happen fast in the right environment. And also that without all that oxygen, it wouldn't have happened at all.