Our Earliest Ancestor Appeared Soon After Earth Formed
Until we learn whether or not life exists on other planets, we extrapolate on the basis of our single living world. Just how long it took life to develop is a vital question, with implications that extend to other planetary systems. In today’s essay, Alex Tolley brings his formidable background in the biological sciences to bear on the matter of Earth’s first living things, which may well have emerged far earlier than was once thought. In particular, what was the last universal common ancestor — LUCA — from which bacteria, archaea, and eukarya subsequently diverged? Without the evidence future landers and space telescopes will give us, we remain ignorant of so fundamental a question as whether life itself — not to mention intelligence — is a rarity in the cosmos. But we’re piecing together a framework that reveals Earth’s surprising ability to spring into early life.
Once upon a time, the history of life on Earth seemed so much simpler. Darwin had shown how natural selection of traits could create new species given enough time, although he did not argue for the origin of life, other than it would start in a “warm pond”. Extant animals and plants had been classified starting with Linnaeus, and evolution was inferred by comparing traits of organisms. Fossils of ancient animals added to the idea of evolution in deep time. In 1924, Oparin, and later in 1929, Haldane, suggested that a primordial soup would accumulate in a sterile ocean, due to the formation of organic molecules from reduced gasses and energy. This would be the milieu for life to emerge.
