Science

High-carbonate lakes explain the origin of life "phosphate problem"

High-carbonate lakes explain t...
Carbonate-rich Mono Lake in California was one of the lakes researchers took phosphorous measurements
Carbonate-rich Mono Lake in California was one of the lakes researchers took phosphorous measurements
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Carbonate-rich Mono Lake in California was one of the lakes researchers took phosphorous measurements
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Carbonate-rich Mono Lake in California was one of the lakes researchers took phosphorous measurements

For decades, scientists have pondered the so-called "phosphate problem" when seeking to understand the origins of life on Earth. The problem revolves around the fact that phosphorous is one of the six key chemical ingredients of life, yet its scarcity raises the question of how early Earth supplied this essential element. A new study has now provided a possible explanation.

The study, conducted by researchers at the University of Washington, looked at lakes rich in carbonate, which form in dry environments when water drains from the surrounding landscape into depressions. Due to the high evaporation rates of these shallow lakes, the waters become highly salty and alkaline solutions, hence their name alkaline or soda lakes.

The researchers examined phosphorous levels in existing carbonate-rich lakes, which are found on all seven continents. Although phosphorous concentrations are affected by when and where samples are taken, the team found that the levels of phosphorous found in such lakes can be up to 50,000 times that found in seawater, rivers and other types of lakes. This led the researchers to believe that there is a common, natural mechanism responsible for the accumulation of the phosphorous in these lakes.

The explanation the team landed on centers on the carbonate content of the lakes. In most lakes, calcium, which is much more abundant than phosphorous, binds with it to form solid calcium phosphate materials that life isn't able to access. However, in carbonate-rich lakes the carbonate takes precedence in binding with the calcium, leaving an amount of the phosphate left over without a dance partner. The researchers conducted lab tests combining different concentrations of ingredients and found that calcium does indeed bind to carbonate, leaving phosphate freely available in the water.

Along shorelines, in pools separated from the lake's main body, or during dry seasons when lake waters evaporate, the researchers say phosphate levels could climb considerably, up to a million times levels found in seawater.

"The extremely high phosphate levels in these lakes and ponds would have driven reactions that put phosphorus into the molecular building blocks of RNA, proteins, and fats, all of which were needed to get life going," says study co-author David Catling, a UW professor of Earth & space sciences.

Adding extra weight to the theory is the fact that the early Earth, when the building blocks of life on Earth were developing, had a very carbon dioxide-rich atmosphere. This would have provided excellent conditions for the creation of carbonate-rich lakes with high levels of phosphorous. Additionally, carbon dioxide from the atmosphere dissolving in water would have created acidic conditions that prompt the release of phosphorous from rocks.

"The early Earth was a volcanically active place, so you would have had lots of fresh volcanic rock reacting with carbon dioxide and supplying carbonate and phosphorus to lakes," says study first author Jonathan Toner, a University of Washington research assistant professor of Earth and space sciences. "The early Earth could have hosted many carbonate-rich lakes, which would have had high enough phosphorus concentrations to get life started."

The study appears in the journal PNAS.

Source: University of Washington

6 comments
Torbjörn Larsson
Biology/geology has over the years narrowed down the locale for the universal ancestor lineage to alkaline hydrothermal vents. However scientists and especially biochemists may disagree and place the locale as early pools or as here lakes. Never mind that we know there was a global ocean but we don't know there was any arc islands (say). This paper supports the latter view as main author Catling often do, but even if the find is interesting the implications are weak. One reason why the paper is weak is that it cherry picks old papers claiming Hadean Earth had little ocean phosphorylating agents. Later papers have found that this is not so. "Here, we report the occurrence of phosphite in early Archean marine carbonates at levels indicating that this was an abundant dissolved species in the ocean before 3.5 Ga." [ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3690879/ ] Phosphite phosporylation does not directly form phosphates (but other organophosphor compounds), but there is another pathway: "We know little of the speciation of P in the lithosphere, especially in melts and non-crystalline materials ... It is possible that pyrophosphate was originally incorporated into prebiotic systems because of its energy-transfer capacity and that the information coding function of P as a constituent of polynucleotides is a secondary property [24]. Another condensed phosphate, the ring-formed trimetaphosphate ((P3O9)3-), has, on the other hand, been shown to be the most effective condensing agent among polyphosphates, particularly because it can serve as a phosphorylating agent reagent in strongly alkaline aqueous solutions (pH 12) [18,25-28]. Such high pH values can be found in, for instance, the fairly recently discovered modern sediment-starved subduction zones with serpentinite mud volcanoes, like the Mariana Trench [29,30]. Serpentine mud volcanoes similar to those of the Mariana forearc next to the trench occur at Isua, Greenland, and have been dated to early Archean (3.81-3.70 Ga) [31]." [ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4057523/ ] So we don't really need acidic lakes and dry/wet cycles to drive phosporylation, and the environment where this would happen is around the alkaline hydrothermal vents of the early global ocean.
paul314
Just a bit ironic that the chemical requirements of modern life should be based on a historical remnant of conditions that could only be relatively common when modern life (and its associated high-oxygen, low-CO2 atmosphere) didn't exist.
HighlanderJuan
Two thoughts. First, Mono Lake is being gradually drained by the city of Los Angeles amid much conflict with locals. Second, I suspect the point about early carbon dioxide rich environments is quite valid, and while the elites who rule the governments are trying to get richer by removing the CO2 from our modern environment, nursery greenhouses still use CO2 generators to help their plants grow. I never thought of myself as an environmentalist, but I do realize that I am now against all forms of government that serve only the needs of the rich and powerful. They seem bent on the idea of controlling everything and every form of animal life. That being said, they have shown themselves they are lousy managers of anything.
paul314
Can we just stop with baloney like "while the elites who rule the governments are trying to get richer by removing the CO2 from our modern environment, nursery greenhouses still use CO2 generators to help their plants grow." Such disinformation is almost as stupid as "It's winter, where's your global warming now". Greenhouses are great for (some) growing plants, not so good for people performing physical labor, complex electronics, or pretty much any other aspect of modern civilization.
Torbjörn Larsson
@paul: Yes, that is evolution for you. When you consider the tricks that plants go through to try to make an anoxic environment around the RuBisCO enzyme the atmosphere they created harms (low selectivity for OO over CO)... On the other hand, if it wasn't for such remaining traits we would be far less knowledgeable about our history (even after genomics came around). @HighlanderJuan: Are you really trying to troll a science article - after a token observation sentence - by promoting political views that tries to overrule the science we rely on? And by using conspiracy theory at that. Last I looked, the majority of nations were at democratic and the number is increasing. At least in true democratic nations there are no dictatorship, elite or not, "ruling" such governments, And those nations as well as many others have joined together to promote the science on man made global warming. (And by the way, CO2 is not the constraint in farming, it is NKP.) As has the majority of people globally, according to polls. [References can be searched, or asked for; but really, this is a boring subject here however socially important in general.] The ironic exceptions are the current populist states, where elite such as Trump and Bolsonero has joined their rich supporters to "serve only the needs of the rich and powerful" and is overruling science when it suits them. AFAIK the analysis of Economist is that US has been "a compromised democracy" starting after the economic troubles in the 30s - I'll take it as the exception that proves the rule. Mostly, shouldn't you insert your irrelevant personal opinion (no references) under climate science articles?
ljaques
Flows to Mono Lake were mandated by the gov't in 1994 and secured in 1998, so it continues to fill, Juan.