Episode 2 of Martin Jenkins’s YouTube series, The Story of Life on Earth, asks how ordinary chemistry first became biology roughly 3.8 billion years ago. The episode walks through the leading theories for the origin of life, from the classic Miller-Urey experiment to hydrothermal vent chemistry, and looks at what that history can tell us about the search for life on Mars.
The episode also covers the physical evidence preserved in Western Australia’s Pilbara Craton, the reconstruction of LUCA, the last universal common ancestor of all life, and the RNA world hypothesis as a bridge between non-living chemistry and self-replicating biology.
The episode connects that early chemistry directly to the search for life beyond Earth. Because Bacteria and Archaea remain the most successful and widespread organisms on the planet today, their biochemistry offers scientists a working model for what to look for on worlds like Europa, Enceladus, and Mars, where similar hydrothermal or subsurface chemistry may exist. Reconstructing LUCA, the last universal common ancestor of every living thing, means working backward from what all of today’s life still has in common, from the genetic code to the core machinery every cell uses to build proteins.
The same deep-time territory runs through Martin’s 2019 book, Life: The First Four Billion Years, illustrated by Grahame Baker-Smith, which traces Earth’s story from the Big Bang through the fossil record and the age of dinosaurs to the first mammals.
None of this is settled science. The Miller-Urey experiment showed that simple organic molecules can form under early-Earth-like conditions, but it didn’t prove that’s how life actually started, and hydrothermal vent chemistry remains a competing, equally plausible starting point. What keeps researchers returning to the Pilbara Craton is that its rocks are among the oldest on the planet still preserving anything resembling a biological signature, which makes it one of the few places where the theory can be tested against physical evidence rather than argued in the abstract.
Watch Episode 2 on YouTube, start from Episode 1, or see the full series on the YouTube Series page.