Photo credit: ESA/NASA
By Marcelo Gleiser
For the past two weeks we’ve been exploring some of the questions related to life’s origin on Earth and possibly elsewhere.
We know life was present on Earth at least 3.5 billion years ago. It may have been present even earlier, but results remain controversial. The window of opportunity for life to emerge and take root here opened after the Late Heavy Bombardment calmed down some 3.9 billion years ago. Before then, conditions were too harsh for living creatures to survive; if anything lived, it was most probably destroyed, leaving no clues. Life’s early history is written in rocks. As primal rocks melted and got mixed and remixed in a churning inferno, life’s early experiments were erased into oblivion.
We can’t know what really happened to life that early on. We can study possible metabolic and genetic pathways to life, collect fossilized evidence from old rocks, and conduct experiments in the laboratory, expanding our understanding of this most vexing of questions, the transition from nonlife to life. But even if we are able to make life in vitro, we can’t be sure that this is what happened around 3.6 billion years ago here.
What we do know is that the history of life in a planet depends on the planet’s life history: change the sequence or intensity of events — asteroid collisions, massive volcanic eruptions, radical changes in atmospheric composition — and life’s history is rewritten.
This casts the question of life here, and elsewhere, into new focus. We can state, with high confidence, that even if there are other intelligent creatures in the universe, even humanoid ones, they won’t be like us. We are the only humans in the cosmos, the product of a very particular set of cosmic, geochemical and evolutionary circumstances. Life is an experiment in natural selection, and an amazingly creative one at that. There may be certain biological patterns that offer an evolutionary advantage and would be fairly common, such as two eyes or left-right body symmetry. But details will vary as they do with snowflakes, all coming from the same chemistry but amazingly diverse due to environmental details.
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