At its core, every cell is just a bubble of chemistry sealed inside a membrane. In modern cells, that chemistry is extraordinarily complex, orchestrating some 1 billion reactions per second. Likewise, its container, the lipid membrane, is built and maintained by elaborate biochemical mechanisms.
But even the much simpler first cells would have needed a bubble too. Without a physical boundary corralling molecules into a small space, whatever it was that turned into early life would have been too dispersed to assemble the complex systems that life requires, said Bruce Damer, an astrobiologist at the University of California, Santa Cruz. In this framework, known as the “lipid first” hypothesis, Earth transitioned from a mess of primordial chemistry to something recognizably alive because of those containers.
But many proponents of the lipid world go even further. They argue that the bubbles did more than hold chemistry. The bubbles themselves began to evolve.
Evolution requires a way for parents to pass traits to offspring. Modern life accomplishes this with complex biochemicals such as DNA and RNA, which can encode and copy information in their sequences. In the 1990s, researchers imagined a different possibility: What if a chemical system, rather than a molecule, could carry heritable information and become subject to evolution?
The idea begins with a puddle of water on the early Earth. The puddle is stocked with all kinds of small organic molecules, some homegrown and some delivered by dust and meteorites. Many of these molecules have a split personality.
One end of them is drawn to water, or “hydrophilic.” The other is repelled by water in the same way that oil is. These “hydrophobic” ends will huddle together to hide from the water, while the hydrophilic ends will face outward. These behaviors cause the molecules to form a tiny sphere — a bubble.
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