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Comment by FrustratedMonky | Hacker News Reader

Or, why aren't Martians from Earth.

As much as I like the idea conceptually for movies. That life on Earth came from Mars still doesn't explain how life started on Mars. It just moves the location, the mechanism is still tbd.

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Life arose on Earth really fast after the surface stopped being magma. Since Mars cooled down faster the idea is that it could have spent 100 million of year developing bacteria which were then seeded the Earth as soon as there was liquid water there.

While in general the argument may hold that life evolved too fast, your numbers are off. 100 million years is just about the minimum estimate for the emergence of life on Earth. If Mars has a longer timeline it should be closer to 1 billion years between solidification and emergence of life.

You're right that my numbers are off. I'd bee thinking of the end of the Late Heavy Bombardment 3.8e9 years go, but there's some suggestive evidence there was liquid was on Earth's surface 4.4e9 years ago. And the earliest bacterial fossils are from 3.5e9 years ago, though goodnesss knows how long it took bacteria to make colonies that ended up making fossils to survive to the present day.

> Or, why aren't Martians from Earth.

Mars's gravity is much lower, so it's much easier for an impact to accelerate rocks to escape velocity.

I agree with the rest of your comment though.

If we can demonstrate that life moved from Mars to Earth then the most likely explanation for life on Mars is that it also got there from somewhere else.

All this has happened before, and it will all happen again.

Yeah I never liked the panspermia as a solution to how life started so quickly on Earth because it just kicks the can down the road. But hey it has been speculated that DNA may be almost 10 billion years old https://phys.org/news/2013-04-law-life-began-earth.html. But this is just a thought experiment, I am unsure if we know how long it takes for DNA to double, nor do we know if the rate would be constant over time. For example if proof reading mechanisms evolved later thus slowing down the rate of change. But it's fun to think about. Too bad Google search is so useless I used to be able to go down these Rabbit holes finding all sorts of information but now it's almost impossible, Google just gives superficial AI answers these days

Recall that no one could reconcile billion year ages for the earth with it not having cooled far more - until the discovery of radioactivity.

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