[ExI] Life Originated Twice on Earth

[John Clark]

*The last universal common ancestor (LUCA) existed between 3.5 and 4.2
billion years ago. LUCA was probably not the first living thing, but
probably was the first to use DNA as its genetic code, before LUCA life
probably used RNA. If there were other independent lines of inheritance
besides LUCA they're not very important because a very long time ago they
all went extinct. More advanced eukaryotic cells like we are made out of
evolved about 2 billion years ago when an ancient archaeon microbe engulfed
an energy producing oxygen-using bacteria which, because of a symbiotic
relationship, evolved into a mitochondria. And life you could actually see
without using a microscope only came into existence 500 million years ago.
And life was only able to make a radio telescope about a century ago. *

*That's one reason I think we are the first. The other is that the universe
has obviously not been engineered. *

*John K Clark*


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