Life is about barriers and compartments. Your body encloses your innards and keeps them separate from the outside world. Each of your cells is also a tightly packaged set of proteins and other essential molecules, bounded by a membrane. All living things are like this and for obvious reasons: Without a membrane, the contents of their cells would rapidly leak away, and become one with their environment. Life cannot exist without barriers and compartments, without some separation between an individual and everything else.
This point seems incredibly obvious, but it has a long history of being ignored.
For example, many discussions about the origin of life involve a mention of “primordial soups”. In these puddles of water, it is said, radiation and lightning fused simple molecules into complex ones. Eventually, this produced the biological chemicals that we rely on today, such as DNA and proteins. It’s a nice image, and one bolstered by Stanley Miller’s classic 1958 experiment, where he electrified a mix of water and simple gases and produced amino acids—the building blocks of proteins.
But the soup hypothesis cannot possibly be right. First, where are the compartments? How do molecules in a diffuse soup find each other with enough regularity to engage in chemical reactions? And when they do bump into each other, why would they react? Complex molecules won’t arise from simple ones on their own. They need a huge supply of energy and a constant one at that. Occasional lightning strikes aren’t going to cut it.
For several years, a small group of scientists have championed a different scenario for the origin of life, which takes it from soupy puddles to the deep ocean. There, hot fluids bubble up from beneath the earth through rocky hydrothermal vents.
One such set of vents can be found at the bottom of the mid-Atlantic Ocean. Rather beautifully, it’s called the Lost City. It’s a field of ghostly white chimneys, made of calcium carbonate (limestone). Hot alkaline fluid, rich in methane and hydrogen, bubbles up through them. There is plenty of life here—snails, shellfish, worms, and microbes galore. And perhaps it’s in places like this that life started in the first place.
All the conditions are right, and a long way from inert soup. The vents are rich with the right basic chemicals, like methane and hydrogen. Their hot churning water provides a constant supply of energy. And they have ready-made compartments—labyrinths of small pores in the chimney’s rocks.
According to people like Mike Russell, and subsequently Bill Martin and Nick Lane, the vent provided a constant supply of fresh basic chemicals, and the necessary heat and energy to combine them into more complex organic ones. These included nucleic acids (the building blocks of DNA) and amino acids (the building blocks of proteins. The rocky pores acted as “proto-cells” that concentrated these molecules and prevented them from diffusing away. Encased in these compartments, they could react with one another, and evolve.
If this hypothesis is right, that’s the point when life emerged. Rather than the fully-formed, free-living cells we know today, the last common ancestor of all living things (known as LUCA) was a hollow piece of rock.
It’s a captivating idea, although there are still many details to flesh out. These scientists are slowly doing that, taking inspiration from the chemistry in the vents, and the biochemistry of the microbes that live there.
Lane and Martin have just published a new paper in the journal Cell that fleshes out more details of the idea, and outlines a critical step: If the first life was an immobile rocky proto-cell, how did it escape from the vents and start an independent existence?
I’ve covered their ideas for Nature News, so head over there to find out the latest chapter in this exciting origin story.
More on the origin of life:
- A network of molecules, building each other at the dawn of life
- A possible icy start for life
- Tree or ring: the origin of complex cells
- The origin of complex life – it was all about energy
- Scientists finish a 53-year-old classic experiment on the origins of life