One and Done

So today we watched a video about the search for life on mars in Evolution of the Earth, and they kept talking about the conditions for life to evolve, the conditions for life to evolve, the conditions for life to evolve. And I'm sitting there wondering, "Wait, so if the conditions for life to evolve are present on Earth, why aren't new forms of life constantly emerging?"

So I sat there for a while with this seriously wigging me out more and more the longer I thought about it. At the end of class I decided to ask the professor why we don't see new creepy-crawlies spontaneously bursting into being all around us.

"Well," he says, "Life changes the atmosphere. Early Earth had methane and ammonia in the atmosphere, and you need those for anything interesting to happen. All the oxygen in the atmosphere is due to photosynthesis."

This goes on. I ask, "So, if hypothetically, life evolved on a planet and was then wiped out, it couldn't evolve again?"

"Not if it changed the atmosphere enough. It could only happen again if the atmosphere changed back."

In short, living organisms are bastards. It's not just humans - EVERY LIVING THING ON THE ENTIRE PLANET, SINCE THE DAWN OF TIME, has been making it progressively less inhabitable for anything that might come after. This is also a pretty good plan for boxing out any other fledgeling life form that tries to get in on your planet - make it useless to them and they'll leave it alone.

So, in short, life is one and done. Once you get it, either it sticks around or it goes extinct and never comes back.

Don't look too hard for a metaphor in this post.