Nearly 150 years ago, Charles Darwin wrote a personal letter to a friend and laid out the scaffolding of what would later be called primordial soup theory: Basically, Earth’s original blend of gases produced a broth of organic molecules when exposed to light and heat, eventually forming the building blocks of life in amino acids. Now, research scientists are lining up more and more evidence that he was probably right.
Not only did Darwin suggest an overall primordial soup—he identified some nuanced ways that a smaller, closed body of water would make a better mix.
In an 1871 letter to a friend, Darwin wrote: “It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present.— But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts,—light, heat, electricity &c present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter [would be] instantly devoured, or absorbed, which would not have been the case before living creatures were formed.”
Eighty years later, scientists finally followed Darwin’s recipe, with added understanding of chemical facts like amino acids that weren’t discovered until decades after Darwin’s letter. With enough amino acid pieces swirling in the same body of water, scientists believe, almost all combinations will end up occurring. The million monkeys have turned to stirring the soup.
There are some key factors here that scientists now believe are critical to a successful primordial soup. And, honestly, you can think of it like a regular soup. Imagine throwing one bouillon cube into an entire stockpot versus a small saucepan full of water. Not only will your stockpot full have very little flavor, it will take forever for the water to heat enough for the bouillon cube to dissolve all the way.
It will even be more difficult to pin down remaining pieces to break up with a wooden spoon. That means a primordial soup with all the same ingredients like different amino acids and electrolytes will respond very differently to sunlight on a small pond versus a large ocean.
And, as the BBC points out, even the size of a small pond varies from day to night and from season to season, making a kind of running experiment that iterates the same materials at every possible concentration and condition:
Pools on land can periodically dry out almost entirely when it gets hot, then fill up again when it rains. Such wet-dry cycles may seem innocuous, but they can have profound effects on the chemicals of life.
[A] 2009 experiment only made two of the four building blocks of RNA. In 2019, researchers in Germany made all four at once. They placed simple carbon-based chemicals in hot water on a mineral surface and subjected them to repeated wet-dry cycles. A few days of this was enough to make the RNA building blocks.