The missing link in the origin of life?

Charles Darwin proposed that life could arise in a “little warm pond” containing the right mix of chemicals and energy. New research conducted by the University of Washington and published in Earth and Environment Communications He highlights a shallow “soda lake” in western Canada as a possible match for these conditions. The results provide new support for the possibility that life emerged from lakes on early Earth, about 4 billion years ago.

Scientists have known that under the right conditions, complex life molecules can emerge spontaneously. As recently demonstrated in the hit film “Chemistry Lessons,” biological molecules can be extracted from inorganic molecules. In fact, long after the real-life discovery of the 1950s Amino acidsthe basic building blocks of proteins. Recent research has made the basic building blocks of proteins RNA. But this next step requires very high concentrations of phosphate.

Phosphate forms the “backbone” of ribonucleic acid (RNA). DNA It is also a major component of cell membranes. The concentrations of phosphate needed to form these biomolecules in the laboratory are hundreds to a million times higher than the levels normally found in rivers, lakes, or in the oceans. This has been called the “phosphate problem” of the emergence of life, a problem that soda lakes may have solved.

Soda lakes as a solution

“I think these soda lakes provide a solution to the phosphate problem,” said lead author David Catling, a professor of Earth and space sciences at the University of Wisconsin. “Our answer is hopeful: This environment must have occurred on early Earth, and perhaps on other planets, because it is just a natural consequence of the way planetary surfaces are formed and how water chemistry works.”

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

Members of the research team walk across the surface of Last Chance Lake in September 2022. At the end of summer, the water almost completely evaporates, leaving a salty crust on the surface. But the water stays down in the pockets and cavities, and the fine sediment settles underneath, creating a crème brûlée structure that's somewhat treacherous to walk on. Credit: Zach Cohen/University of Washington

Previous research conducted by the University of Wisconsin in 2019 found that the chemical conditions for the emergence of life could theoretically occur in soda lakes. The researchers combined chemical models with laboratory experiments to show that natural processes could theoretically concentrate phosphate in these lakes to levels up to a million times higher than in ordinary water.

Last Chance Lake: a natural laboratory

For the new study, the team set out to study such an environment on Earth. Coincidentally, the promising candidate was just a short drive away. Tucked away at the end of a Master's Thesis From the 1990s the highest natural phosphate level known in the scientific literature was at Last Chance Lake in British Columbia's interior, Canada, about a seven-hour drive from Seattle.

The lake is about one foot deep and contains turbid water with fluctuating levels. It is located on federal land at the end of a dusty dirt road on the Caribou Plateau, in British Columbia's cattle country. The shallow lake meets the requirements of a soda lake: a lake above volcanic rock (in this case, basalt) combined with a dry, stormy atmosphere that evaporates incoming water to keep water levels low and dissolved compounds concentrated within the lake.

Implications for life on other planets

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

This panoramic view shows Last Chance Lake in western Canada in November 2021, when the lake had shrunk into many small ponds and ice had formed over each pond. Two researchers from the University of Washington stand on the lake's icy surface. Source: Kimberly Bobbie Sinclair/University of Washington

“We studied the natural environment that should be common throughout the solar system. Volcanic rocks are common on planetary surfaces, so it is possible that the same water chemistry occurred not only on early Earth, but also on the oldest planets. Mars And early Venus“If liquid water exists,” said lead author Sebastian Haas, a postdoctoral researcher at the University of Wisconsin in Earth and Space Sciences.

Field research and results

The University of Wisconsin team visited Last Chance Lake three times from 2021 to 2022. They collected observations in early winter, when the lake was covered in ice; In early summer, when water in rain-fed springs and snowmelt-fed streams reaches its highest levels; In late summer when the lake was almost completely dried up.

“You have this dry salt that looks flat, but there are nooks and crannies. Between the salt and the sediment there are little pockets of water with a high percentage of dissolved phosphate,” Haas said. “What we wanted to understand was why and when this could have happened on ancient Earth.” “In order to provide a cradle for the origin of life.”

On all three visits, the team collected samples of water, lake sediments and salt crust to understand the lake's chemistry.

In most lakes, dissolved phosphate quickly combines with calcium to form calcium phosphate, the insoluble substance that makes up tooth enamel. This removes phosphate from the water. But in Lake Last Chance, calcium combines with abundant carbonate as well as magnesium to form dolomite, the same mineral that forms picturesque mountain ranges. This reaction was predicted by previous modeling work and was confirmed when dolomite was abundant in the sediments of Lake Last Chance. When the calcium turns into dolomite and does not remain in the water, the phosphate lacks a bond partner, so its concentration rises.

Conclusion and future research directions

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

The study also compared Last Chance Lake with Goodenough Lake, a lake about 3 feet deep with clearer water and different chemistry just a two-minute walk away, to find out what makes Last Chance Lake unique. The researchers wondered why life, which is present in all modern lakes at some level, did not use phosphate in Lake Last Chance.

Lake Goodenough contains mats of cyanobacteria that extract or “fix” nitrogen gas from the air. Cyanobacteria, like all other life forms, also require phosphate, and their growing population is consuming some of the phosphate supply in the lake water. But Last Chance Lake is so salty that it inhibits the organisms that do the energy-intensive work of fixing atmospheric nitrogen. Last Chance Lake harbors some algae but does not have enough nitrogen to host more life, allowing phosphate to build up. This also makes it a better counterpart to the lifeless Earth.

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

Reference: “Biogeochemical explanations for the world's largest phosphate-rich lake, a counterpart to the origin of life” by Sebastian Haas, Kimberly Poppy Sinclair, and David C. Catling, 9 January 2024, Earth and Environment Communications.
doi: 10.1038/s43247-023-01192-8

The research was funded by the Simons Foundation. The other co-author is Kimberly Bobbie Sinclair, a UW graduate student in Earth and space sciences. Graduate students in the University of Wisconsin's astrobiology program also helped collect samples.