Were Large Soda Lakes Cradle Of Life?

Along with nitrogen and carbon, phosphorus is an essential element for life on Earth. It is a central component of molecules such as DNA and RNA, which serve to transmit and store genetic information, and ATP (adenosine triphosphate), which cells need to produce energy.

Phosphorus may also have played a key role in the origin of life. Certain conditions are needed to trigger the start of the biochemical processes that precede life. One of these is the presence of sufficient phosphorus. Its availability regulates the growth and activities of organisms. Unlike nitrogen or carbon, however, phosphorus is relatively rare at Earth's surface - which was the case in the era before life existed as well as today.

It is precisely because phosphorus is rare and so difficult to obtain, yet subject to high demand by living organisms, that scientists have long wondered how life could have arisen at all.

To answer this question, they conducted experiments in the laboratory. These showed that prebiotic chemistry requires very high concentrations of phosphorus - about 10,000 times more phosphorus than naturally occurs in water. This raises the question of how and where such high concentrations of phosphorus in water occurred on Earth billions of years ago.

Earth scientist Craig Walton has a new answer: large soda lakes without natural runoff could maintain phosphorus concentrations for a sufficiently long time, even if life begins to exist in them at some point (and continuously consumes phosphorus). The results of the study have just been published in the journal Science Advances.

Such lakes lose water only through evaporation. This means that phosphorus is left in the water instead of being washed away through rivers and streams. As a result, very high concentrations of phosphorus can build up in these soda lakes.

As early as 2020, researchers from the University of Washington had suggested that soda lakes could be the cradle of life. Walton has now taken this further. The researcher is investigating questions about the origin of life from a geochemical perspective as part of a Nomis fellowship at ETH Zurich's Centre for Origin and Prevalence of Life (COPL).

Not every soda lake is suitable; Walton excludes small ones. "As soon as life develops in them, their phosphorus supply would be depleted faster than it is replenished. This would nip in the bud both the chemical reactions and the developing life," says Walton. In large soda lakes, on the other hand, the phosphorus concentrations are high enough to sustain both the basic chemical reactions and life over the long term. These high concentrations are achieved through a high volume of inflowing river water, which contains phosphorus, while water only leaves the lake through evaporation. Since phosphorus does not evaporate easily, it stays behind and accumulates in the lake.

One example of such a large soda lake is Mono Lake in California. It is about twice the size of Lake Zurich. In Mono Lake, the phosphorus concentration remains constantly high, allowing a wide variety of organisms to flourish. This is crucial because in small lakes, the phosphorus is used up before new amounts can be formed. Phosphorus in Mono Lake is therefore maintained at a high concentration, which means that a lot of phosphorus regularly flows in without the phosphorus content dropping too quickly.

Walton and his team therefore consider large soda lakes that had a constant high phosphorus supply in the early history of the Earth to have been an ideal environment for the origin of life. The researchers assume that life is more likely to have originated in such large bodies of water than in small pools, as Charles Darwin had suspected.

The origin of life could therefore be closely linked to the special environment of large soda lakes, which, due to their geological setting and phosphorus balance, provided ideal conditions for prebiotic chemistry. "This new theory helps to solve another piece of the puzzle of the origin of life on Earth," says Walton.