Read: A break in the search for the origin of complex life

First, the easy bit. Early cell membranes were built from fatty acids—molecules that look like lollipops, with round heads and long tails. The heads enjoy the company of water; the tails despise it. So, when placed in water, fatty acids self-assemble into hollow spheres, with the water-hating tails pointing inward and the water-loving heads on the surface. These spheres can enclose RNA and proteins, making protocells. Fatty acids, then, can automatically create the compartments that were necessary for life to emerge. It almost seems too good to be true.

And it is, for two reasons. Life first arose in salty oceans, and salt catastrophically destabilizes the fatty-acid spheres. Also, certain ions, including magnesium and iron, cause the spheres to collapse, which is problematic since RNA—another key component of early protocells—requires these ions. How, then, could life possibly have arisen, when the compartments it needs are destroyed by the conditions in which it first emerged, and by the very ingredients it needs to thrive?

Caitlin Cornell and Sarah Keller have an answer to this paradox. They’ve shown that the spheres can withstand both salt and magnesium ions, as long as they’re in the presence of amino acids—the simple molecules that are the building blocks of proteins. The little suns that Cornell saw under her microscope were mixtures of amino acids and fatty acids, holding their spherical shape in the presence of salt.

I find that utterly magical. It means that two of the essential components of life, a protocell’s membrane and its proteins, provided the conditions for each other to exist. By sticking to the fatty acids, the amino acids gave them stability. In turn, the fatty acids concentrated the amino acids, perhaps encouraging them to coalesce into proteins. From the very beginning, these partners were locked in a two-step dance that continued for 3.5 billion years, and helped create all the richness of biology from a starting place of mere chemistry. “I agree completely,” Keller tells me. “It’s completely magical. You need those two parts together.”

“It’s fantastic work,” says Neal Devaraj, of UC San Diego. “Their suggestion that membranes could promote the synthesis of [proteins] is really fascinating.”

This discovery happened almost by accident. Originally, Keller set out to address a different problem, posed to her by her colleague Roy Black. He noted that no one had good ideas about how exactly the protocell trinity—RNA, proteins, and membranes—actually assembled in the first place. It seemed that people were just waving their hands and attributing this crucial convergence to some random event. Black, instead, suggested that the membranes themselves were key. If fatty acids can stick to the constituents of both proteins and RNA, they could have gathered these building blocks together as they themselves assembled.