Scientists have discovered a lake that could be a good match for Darwin's "warm little ponds" where life got started on the primordial Earth.
A team of scientists from the University of Washington made the discovery when they found a shallow "soda lake" in western Canada that seems to have the chemistry and conditions that a small body of water would have needed to facilitate the spontaneous synthesis of complex molecules that led to the emergence life on Earth around 4 billion years ago.
Soda lakes like the one in this research focuses on are small bodies of water containing high levels of dissolved carbonates and sodium, similar to having a large amount of baking soda dumped into them. In this case, though, the high levels of dissolved sodium and carbonate are caused by reactions between water and volcanic rocks.
The findings could help solve a long-standing problem in explaining how life on Earth emerged and could also be applied to other planets in the solar system, like Mars and Venus.
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Since the 1950s, researchers have been able to coax biological molecules like amino acids and the building blocks of RNA from inorganic molecules, but there is a long-standing problem with the next step of this process. RNA and DNA, the key molecules of life, as well as the membranes of living cells need a backbone of naturally occurring molecules of the element phosphorous, known as phosphates.
Concentrations of phosphates needed to form biomolecules in the lab are up to 1 million times higher than the levels normally found in rivers, lakes or oceans. This has become known as the "phosphate problem" in theories of the emergence of life on Earth, and this new research suggests soda lakes could be the solution.
"I think these soda lakes provide an answer to the phosphate problem," research senior author and University of Washington professor of Earth and space sciences David Catling said in a statement. "Our answer is hopeful: This environment should occur on the early Earth, and probably on other planets, because it's just a natural outcome of the way that planetary surfaces are made and how water chemistry works."
Why are soda lakes potential cradles for life
In addition to high levels of dissolved carbonates and sodium, soda lakes also contain large amounts of phosphates, with a 2019 study revealing that concentrations of these molecules in these small bodies of water can be up to 1 million times greater than found in typical bodies of water. That means soda lakes could be the ideal sites for key molecules of life to emerge.
To test this, the University of Washington set about examining just such a soda lake, settling on Last Chance Lake, a 1-foot-deep (30 cm) murky lake found at the end of a dirt road on the Cariboo Plateau in British Columbia, Canada. This particular soda lake was determined to have the highest known phosphate level in the 1990s.
Not only does Last Chance Lake have volcanic basalt rock at its bottom, but it also experiences a dry, windy climate that keeps water levels low and dissolved compounds concentrated by quickly evaporating incoming water.
Scientists behind this new research visited the lake three times between 2021 and 2022, both in summer and when it was frozen over in winter.
"You have this seemingly dry salt flat, but there are nooks and crannies. And between the salt and the sediment, there are little pockets of water that are really high in dissolved phosphate," team member and University of Washington postdoctoral researcher Sebastian Haas said. "What we wanted to understand was why and when could this happen on the ancient Earth, in order to provide a cradle for the origin of life."
After examining the samples of water, lake sediment and salt crust found in Last Chance Lake to understand the lake's chemistry, the team found that calcium had combined with plentiful carbonate and magnesium to form dolomite.
This is different from the situation in other lakes where phosphate usually bonds with calcium to make calcium phosphate, which makes up the enamel on our teeth and is insoluble, depleting levels of phosphates.
As a result of calcium being locked up in dolomite in Last Chance Lake, there are plenty of leftover free phosphates; if these conditions were found in water pools around 4 billion years ago, this would allow the key ingredients for the origin of life chemistry to exist in the necessary high concentrations.
Not only did the team find that Last Chance Lake suggests soda lakes are strong candidates for sites where life could have started on Earth, but they expect the conditions of these lakes to be common to other solar system bodies and across planets outside the solar system, extrasolar planets, or exoplanets.
"We studied a natural environment that should be common throughout the solar system," Haas said. "Volcanic rocks are prevalent on the surfaces of planets, so this same water chemistry could have occurred not just on early Earth, but also on early Mars and early Venus if liquid water was present."
"These new findings will help inform origin-of-life researchers who are either replicating these reactions in the lab or are looking for potentially habitable environments on other planets," Catling concluded.
The team's research is published in the journal Nature Communications Earth & Environment.
