The Case of the Missing Unrelated Life

Question from John:
I am comfortable with evolution and natural selection as a theory for the diversity of life today. One thing lingers as an anomaly, pointing at a non accidental creation. This anomaly is the lack of other “trees of life”. There is not a vestige or hint of any other tree of life but our own (witnessed by the same methods of protein synthesis in a bacterium as in a human).

Where are the other, accidental, spontaneous beginnings of life that began in dirty puddles of water, 2 billion years ago or last Thursday?

Any takers?

Answer by SmartLX:
The earliest evidence of life on Earth amounts to trace elements in rocks from 3.85 billion years ago (see this article) and could have come from anyone’s tree of life, not just our own. Only at the point where we can discern the shape or actions of the life that existed, in evidence that dates hundreds of millions of years later, can we begin to gather morphological, geographical or behavioural evidence that might determine the lifeforms are related to us.

That said, the conditions for life to arise are unknown mostly because they don’t seem to appear in the modern world. It’s reasonable to suppose that they don’t, as the world was a very different place 3-4 billion years ago. Even back then, the right conditions could have been so incredibly rare that abiogenesis only happened in a very localised area (and not necessarily a puddle; see how many other models there are) and never again.

Regardless, once our earliest microscopic ancestors got going, they spread like wildfire. They got everywhere, and their microscopic descendants are still everywhere, even in places we think of as lifeless. They’re in the air we breathe, they’re in the earth we walk on, they’re at the bottom of the sea and coating its surface, they’re rolling along in the desert sands. Any unrelated organisms that arose after that point, or weren’t as well-established at the time, had to compete with this ubiquitous organic juggernaut of carbon-based life. If they ever existed, they’ve been eaten, dismembered, crushed, drowned, strangled, suffocated or starved by our own guys, and any evidence they left has been mistaken for evidence of the roots of our own “tree”. History is written by the winners, as they say, and prehistory is probably no different.