Earth and Mars and Life

Here's something to think about.

If all these statements, which are conventional wisdom in the paleontology/paleoplanetology world, are true, there's a problem.

• Life originated about as quickly on Earth as possible after conditions on this planet settled down to the point where water remained liquid and the planet was no longer being bombarded by numerous large impacts that had the effect of melting the surface of the planet repeatedly; about 4 by ago.

• Given the presence of minute amounts of liquid water on Mars and the known existence on earth of extremophiles that can live chemoautotrophically deep beneath the surface of Earth, present day Earth life could almost certainly find a toehold and survive on Mars.
  
• Conditions on ancient Mars were more hospitable, with a thicker atmosphere and liquid water, earlier than on Earth.

• No evidence has arisen for the existence of life on Mars.

See, either life should have originated on Mars during its period of brief hospitableness to life (in which case a very real possibility exists that life on Earth is actually from Mars), and we should expect to find life beneath the surface of Mars, hanging on, as it were, for dear life, OR, the first premise above, which implies that life always arises very soon after conditions for its existence arise and stabilize, is wrong. Perhaps, after all, the origin of life on Earth was extremely fortuitous, and often conditions for life may exist, but life does not arise.

Stay tuned. We may have the answer to this conundrum in the not too distant future.