Thread: Would evolution follow completely different pattern now?

If all life on Earth was wiped out today, could life start again from scratch? Would it follow a similar pattern to before? Or are there too many environmental variables? Would there be time for intelligent life to evolve again from nothing before the Earth is absorbed into the Sun?

Pretty unlikely everything would be wiped out since life exist deep into the crust. If something melted the entire crust well than you'd have a planet under a much brighter sun and far more distant moon than 3.5+ billion years ago when life started here the first time around--mostly likely meaning a different path to evolution.

The questions you ask are not of science They are metaphysical because science does not yet understand the beginning of life or even diversity of life. Science has yet to identify the processes responsible for generating a new species. We don't know how multicelled organisms came to be. We don't understand the origin of sexual reproduction. We don't even understand the generation of new functional protein systems or new gene regulation or developmental controls.

I am sorry to say that responses carry about as much weight as a fairy tale.

Originally Posted by Monga

If all life on Earth was wiped out today, could life start again from scratch? Would it follow a similar pattern to before? Or are there too many environmental variables? Would there be time for intelligent life to evolve again from nothing before the Earth is absorbed into the Sun?

There is some reason to believe that the development of self - replicating molecules may have required an environment very different than any that exist on Earth today, so it is formally possible that life could not form on the earth as it stands at present.

My belief is that it could form again but some evidence suggests that it might not.

Absolutely evolution could take a very different path, as evidenced by the great extinction events followed by explosions of different regimes of megafauna.

Originally Posted by Monga

If all life on Earth was wiped out today, could life start again from scratch?

As already pointed out it would be difficult to completely eliminate all life on Earth without coming very close to completely destroying the planet. Let's run with the hypothetical premise that 'something' has eliminated all life. Even here we run into imponderables whose answers would have a major impact on the possible answers.

Life almost certainly arose with the benefit of the rich array of moderately complex organic molecules delivered by comets and asteroids during the Heavy Bombardment phase. Where are these complex organic molecules in your proposed scenario? If life was eliminated by a massive impact that melted the crust then nearly all of those are now absent and there is no continuing rain of bolides to lead to the primordial soup that produced or sustained the first terrestrial life.

It took three billion years for life to evolve to the point where it could move onto land. In three billion years the thermal output of the sun will be too great to permit liquid water on the Earth, so there is no plausible chance of recovering something like, or unlike, our present complex lifeforms.

Also, depending upon the way life is eliminated, there are major questions about how would the biomass carbon now be distributed between carbonates, ocean and atmosphere at what would the impact of this be on climate. Plus, the removal of life would have a huge impact on geology; the role of life in modifying geological processes tends to be overlooked.

We could easily list a dozen other aspects of your hypothetical that would quite alter the resultant picture. To properly answer your question, or at least to attempt a proper answer, you would need to be more specific.

Even where we envisage going back to the initial conditions of a primeval Earth we find no certainty. Gould famously remarked that 'replaying the tape of life' would produce the same outcome every time. In contrast Conway Morris suspects that life will always tend to intelligent, oxygen breathing bipedal entities. This is what happens when you try to extrapolate from a sample size of one.

Monga

I suggest you re-phrase your enquiry. A possible way is to ask what would happen if there was another Earth size planet of similar chemical make-up to the primeval Earth, that was in a similar orbit around a similar sun.

What are the chances of it developing life?
What is the likely course of evolution on such a planet assuming the physico-chemical and astronomical conditions remained similar to that which Earth has experienced?

I am certain in my own mind that there are a substantial number of such planets in our galaxy. Perhaps that question might be more appropriate??

Something like that happened, on a smaller scale, when the continents split up on this earth.

And evolution did follow different paths on the different continents. But not totally different in all respects - there are common themes.

I think we could realistically tackle the question as put. Suppose 50% of living material, both on land and in the oceans, dies over course of weeks or months. That's not really unthinkable. So: dead trees, wilted lawns, the ocean surface festering with bloated bobbing fish. Catastrophic decay. I imagine this would quickly throw the remaining ecology and climate completely out of whack, rapidly killing most of the surviving biomass. A new regime is going to set in isn't it? Is this new regime (i.e. atmospheric feedback) hostile to original lifeforms? Mostly... probably..? Then we have a condition that truly does wipe out all besides maybe anaerobics, extremophiles, depending on what new loop takes over. This has happened before.

Speculations regarding the scenario? I'm wondering most about immediate effect of rotting half the organisms in our biosphere. It's a lot of fish. Gosh, even think of the deadwood going up in smoke.

Pong

The end of Permian extinction event killed off 98% of all life on planet Earth, as far as we can tell from the fossil record. The triggering event seems to be the Siberian volcanoes. Perhaps the most massive set of eruptions in Earth's history?

How this killed so much is still a bit moot. One theory is that it was due to emissions of hydrogen sulphide by an upsurge in anaerobic bacteria.

The result was the beginning of the Triassic era, with its new animal life, including some of the most dramatic terrestrial animals ever seen. Would these life forms have come about without the extinction event? Your guess is as good as mine.

Hm. Thinking about this, plus Ophiolite's recent remark that the effect of plant life on geology is often underrated, gives credit to the Gaia "hypothesis". I think that if it was renamed the Gaia "perspective" people would accept it. Kinda like we now free apply an evolutionary perspective in fields that have nothing to do with genetics.

One man's trash is another man's treasure.

Pong

The concept of Gaia is OK, if kept in perspective. If we think of it as simply a connection between all ecosystems, so that, on a special level, we can regard the biosphere of Earth as being one single ecosystem, then we can accept this version.

The problem, as always, is those nutters who take the idea too far and go all mystical on us.