Earth was born around 4.5 billion years ago. It was a young, hot planet swirling with magma and bombarded by asteroids and meteorites that left behind gaping craters. Molten rock hardened into crust and was taken over by a vast ocean, in which hydrothermal vents blasted water heated by the scorching magma in the mantle. It was from this primordial sea of fire that the first forms of life emerged.
In 2013, fossils of microbial life nearly as old as Earth itself were unearthed from the Sun-baked basalts of Australia’s Pilbara Craton. These were stromatolites—sedimentary formations made by microorganisms that thrived in ancient floodlands that had long since dried. At nearly 3.5 billion years old, they were thought to be the oldest evidence of life, until even older microfossils that went back 3.77 billion years were found in Canada four years later. The findings from an ancient hydrothermal vent that used be at the bottom of the ocean seemed to support the hypothesis that this is the type of environment the first life crawled out of.
What even these relics can’t answer, however, is how their common ancestor came into being. Neither can the carbon trapped in 4.1-billion-year-old zircons, which might be a sign of life arising even earlier. Could elements combining into prebiotic molecules, and those molecules creating something more complex, have led to something that could be called alive? Most scientists who investigate the beginnings of life propose some version of this idea.
Biologist Robert Endres of Imperial College in London is not ruling out the possibility of abiogenesis, or nonliving matter going through processes that would eventually give rise to living organisms. But he is also not dismissing the possibility that life might have been brought here by intelligent extraterrestrials that somehow terraformed the planet.
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