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Phosphorus is one of the six basic elements for life, along with oxygen, hydrogen, nitrogen, carbon and sulfur. When combined with oxygen, phosphates are created, necessary for the formation of DNA and RNA molecules.

Phosphates are also an essential part of our bones and teeth, and feed fundamental chemical reactions inside our cells. Although we have known the importance of this chemical compound for decades, its role in the origin of life remains largely a mystery.

"What we call the phosphate problem persists in studies on the origin of life for 50 years, " explains Jonathan Toner, a researcher at the University of Washington. A problem that could explain how the transition from prebiological chemistry to cellular chemistry occurred. In other words: how life could break through in a world without living beings. A study published Monday in the Proceedings of the National Academy of Sciences (PNAS) magazine describes a possible starting point: salty lakes rich in carbonates.

This type of lakes is formed in very dry environments, inside depressions of the land that channel the surrounding water. Its high evaporation rates result in saline and alkaline solutions (high pH solutions). Therefore, they are also known as alkaline lakes or soda lakes. These formations are scattered across the seven continents, so the scientists decided to analyze the phosphorus concentration in several of them: the Monkey in California, the Magadi in Kenya and the Lonar in India.

Ingredients for life

Although the exact levels of phosphorus vary depending on where the samples are taken and the season of the year, researchers have shown that they are about 50,000 times higher than those found in seas, rivers or other lakes . "What makes carbonate-rich lakes a great candidate [to house the origin of life] is that it is a unique environment, with phosphate in concentrations high enough to react with organic molecules," Toner notes. .

"In addition, they contain different microenvironments (isolated pools, a main body of water, riverbanks), so many different reactions could occur, creating the molecular building blocks of RNA, proteins and fats. Everything you need to put life going on . "

These lakes appear in atmospheres with a high content of carbon dioxide. In fact, it is the presence of carbonic acid salts that is responsible for that high phosphorus content; In other bodies of water, calcium - a very abundant mineral - binds phosphorus to form calcium phosphate, in which life cannot thrive.

But, in carbonate-rich waters, it is this compound that monopolizes calcium, leaving a part of the free phosphate in the water. "When water evaporates in the sea, it is not enriched in phosphate. This only occurs in carbonate-rich lakes ," explains the researcher. "The reason is that the proportion of calcium is much higher than that of phosphate, so during evaporation calcium combines with all phosphate and removes it from the solution."

Primal Lakes

4,000 million years ago, the Earth's rich carbon dioxide air offered the ideal environment for these lakes to appear. The planet then had great volcanic activity, which would generate large amounts of rock that would react with CO2, providing carbonate and phosphorus.

When the CO2 dissolved in the water, acidity conditions would have been created that would efficiently release the phosphorus from the rocks. "It's a simple idea, that's why it's so attractive," says Toner. "In addition, it solves the phosphate problem in an elegant and plausible way ."

Today, some of these carbonated lakes, such as the Magadi of Kenya, are also rich from a biological point of view, and harbor life that ranges from microscopic levels to large flocks of flamingos. And all these living beings affect the chemistry of the lake.

Therefore, the researchers conducted laboratory experiments isolating carbonate-rich water in different compositions. Its objective was to understand how phosphorus accumulates and how high concentrations of this element can appear in scenarios where there is no trace of life.

Another recent study by the same team had already shown that this type of salt lakes can also provide abundant amounts of cyanide, important in the formation of amino acids and nucleotides, two basic components of proteins, DNA and RNA.

Cyanide is poisonous to humans, but not to primitive microbes, and is critical to the type of chemical reaction that would have created the building blocks of life. "My opinion is that life appeared in a specific environment , which is also a dominant opinion in the community that studies the issue," summarizes Toner.

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