Around four billion years ago, the first building blocks of life emerged on Earth from inorganic molecules. However, this required significantly higher concentrations of the mineral phosphate than normally occur under natural conditions. Researchers have now come across a possible solution to this puzzle: shallow soda lakes such as Last Chance Lake in Canada show the conditions under which phosphate can accumulate significantly. Lakes on early Earth may have provided similar conditions. Other planets with water and volcanic rock could also meet the requirements for the development of life.
Under the right conditions, the complex molecules of life can arise spontaneously from inorganic molecules. Researchers have already reconstructed these steps in the laboratory. So they created both amino acids, the building blocks of proteins, and nucleotides, the building blocks of DNA and RNA. The problem is that the phosphate concentrations required for this are millions of times higher than the values that usually occur in the earth's waters.
Exceptional environmental conditions
A team led by Sebastian Haas from the University of Washington in Seattle has now found a possible solution to this so-called phosphate problem. Certain lakes on Earth, called soda lakes, contain exceptionally high concentrations of numerous minerals, including, in some cases, phosphate. In previous studies, the team had already shown using laboratory experiments and chemical models that phosphate can accumulate significantly in these lakes through natural processes. The concentration achieved in this way could be sufficient to enable the creation of biomolecules.
For the current study, Haas and his team examined one of these soda lakes, Last Chance Lake in the Canadian province of British Columbia. The lake is only about one meter deep and is located on volcanic basalt rock. The water dissolves minerals such as sodium, carbonate, magnesium and phosphate from this rock. The surrounding atmosphere is dry and windy, causing a lot of water to evaporate. This concentrates the minerals in the lake. “There is no other body of water known in the world with a higher naturally occurring phosphate concentration,” say the researchers.
How phosphate accumulates
At different times of the year, Haas and his team took samples from the lake and its sediment and examined the chemical processes. They discovered that various processes work together so that the phosphate can accumulate and is not converted into other compounds. In most other lakes, phosphate reacts with calcium and is deposited as calcium phosphate. In Last Chance Lake, on the other hand, the calcium reacts primarily with the abundant carbonate and magnesium. The phosphate therefore remains free. It is also hardly broken down by biological processes because the lake is too salty for most creatures that could consume phosphate.
“This study adds to the growing evidence that evaporating sodium lakes provide an environment that meets the chemical requirements for the origins of life,” says Haas colleague David Catling. “Basalt rock was probably widespread on the early Earth, so it is plausible that soda lakes formed and provided the basis for the emergence of life.” Since the atmosphere and water then contained less oxygen than today and life was not yet present , which could have consumed phosphate, the concentrations in the ancient natron lakes were probably even higher.
Also on other planets?
According to the researchers, similar conditions would also be possible on other planets. “Volcanic rocks occur on the surfaces of many planets, so the same water chemistry could have occurred not only on early Earth, but also on early Mars and early Venus, if liquid water was present,” says Haas. According to the researchers, the Last Chance Lake offers unique insights into the conditions under which life on Earth could have emerged four billion years ago - and what conditions must be met on other planets for similar processes to take place there.
Source: Sebastian Haas (University of Washington, Seattle) et al., Communications Earth & Environment, doi: 10.1038/s43247-023-01192-8