Shallow soda lakes show promise as cradles of life on Earth

Charles Darwin proposed that life could have emerged in a “warm little pond” with the right cocktail of chemicals and energy. A study from the University of Washington, published this month in Earth and Environment Communications, reports that a shallow “soda lake” in western Canada shows promise for meeting these requirements. These results confirm that life could have emerged from lakes in the early days of the Earth, around 4 billion years ago.

Scientists know that under the right conditions, the complex molecules of life can emerge spontaneously. As recently revealed in the hit film “Lessons in Chemistry,” biological molecules can be made to form from inorganic molecules. In fact, long after amino acids, the building blocks of proteins, were actually discovered in the 1950s, more recent work created the building blocks of RNA. But this next step requires extremely high phosphate concentrations.

Phosphate forms the “backbone” of RNA and DNA and is also a key component of cell membranes. The concentrations of phosphate required to form these biomolecules in the laboratory are hundreds to a million times higher than the levels normally found in rivers, lakes or the ocean. This is the so-called “phosphate problem” linked to the emergence of life, a problem that soda lakes could have solved.

“I think these soda lakes provide an answer to the phosphate problem,” said lead author David Catling, a UW professor of earth and space sciences. “Our answer is hopeful: this environment should occur early on Earth, and probably on other planets, because it is simply the natural result of how planetary surfaces are created and how the planet works. water chemistry.”

Soda lakes get their name from their high levels of dissolved sodium and carbonate, similar to dissolved baking soda. This results from reactions between the water and the volcanic rocks below. Soda lakes can also contain high levels of dissolved phosphate.

Previous UW research conducted in 2019 found that the chemical conditions suitable for life to emerge could theoretically occur in soda lakes. The researchers combined chemical models with laboratory experiments to show that natural processes can theoretically concentrate phosphate in these lakes to levels up to 1 million times higher than in typical waters.

For the new study, the team decided to study such an environment on Earth. Coincidentally, the most promising candidate was just a short drive away. At the end of a master’s thesis from the 1990s was the highest level of rock phosphate known in the scientific literature, at Last Chance Lake in the interior of British Columbia, Canada, at approximately seven hour drive from Seattle.

The lake is about a foot deep and has murky water with fluctuating levels. It sits on federal land at the end of a dusty dirt road on the Cariboo Plateau, in British Columbia’s cattle ranching region. The shallow lake meets the requirements of a soda lake: a lake on top of volcanic rock (in this case, basalt) combined with a dry, windy atmosphere that evaporates incoming water to maintain water levels. low water and concentrates the compounds dissolved in the lake.

The analysis published in the new paper suggests that soda lakes are good candidates for the emergence of life on Earth. They could also be candidates for life on other planets.

“We studied a natural environment that should be common throughout the solar system. Volcanic rocks are widespread on the surfaces of planets, so this same water chemistry could have occurred not only on early Earth, but also early Mars and early Venus, if liquid was present. water was present,” said lead author Sebastian Haas, a UW postdoctoral researcher in Earth and space sciences.

The UW team visited Last Chance Lake three times between 2021 and 2022. They collected observations in early winter, when the lake was covered in ice; in early summer, when rain-fed springs and snowmelt-fed streams raise the water to its peak; and at the end of summer, when the lake was almost completely dry.

“You have this seemingly dry salt desert, but there are nooks and crannies. And between the salt and the sediment, there are little pockets of water that are very high in dissolved phosphate,” Haas said. “What we wanted to understand was why and when this might have happened on ancient Earth, in order to provide a cradle for the origin of life.”

During the three visits, the team collected samples of water, lake sediment and salt crust to understand the lake’s chemistry.

In most lakes, dissolved phosphate quickly combines with calcium to form calcium phosphate, the insoluble material that makes up the enamel of our teeth. This removes phosphate from the water. But in Last Chance Lake, calcium combines with abundant carbonate and magnesium to form dolomite, the same mineral that forms picturesque mountain ranges. This response was predicted by previous modeling work and confirmed when dolomite was abundant in the Last Chance Lake sediments. When calcium turns into dolomite and does not remain in water, phosphate does not have a binding partner and therefore its concentration increases.

“This study adds to growing evidence that evaporative soda lakes are environments that meet the requirements for the chemistry of the origin of life by accumulating key ingredients at high concentrations,” Catling said.

The study also compared Last Chance Lake to Goodenough Lake, a lake about three feet deep with clearer water and different chemistry just a two-minute walk away, to find out what makes Last Chance Lake unique. Researchers wondered why life, present at some level in all modern lakes, was not using the phosphate from Last Chance Lake.

Goodenough Lake has mats of cyanobacteria that extract or “fix” nitrogen gas from the air. Cyanobacteria, like all other life forms, also need phosphate and their growing population consumes part of the phosphate reserves in the lake water. But Last Chance Lake is so salty that it inhibits living things that do the energy-intensive work of fixing atmospheric nitrogen. Last Chance Lake supports some algae but does not have available nitrogen to support more life, allowing phosphate to build up. This also makes it a better analogue for a lifeless Earth.

“These new findings will help inform origin-of-life researchers who replicate these reactions in the laboratory or look for potentially habitable environments on other planets,” Catling said.