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Ancient Salt Rock Shows How A Substantial “Fire Hose” Of Oxygen Entered Our Atmosphere 2 Billion Years Ago

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Madison Dapcevich

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Madison Dapcevich

Freelance Writer and Fact-Checker

Madison is a freelance science reporter and full-time fact-checker based in the wild Rocky Mountains of western Montana.

Freelance Writer and Fact-Checker

A 2-billion-year-old salt (pink-white recrystallized halite) with embedded fragments of calcium sulfate from a geological drill core in Russian Karelia. Photo by Aivo Lepland, Geological Survey of Norway; courtesy of Science/AAAS

In Russia, salts left over from ancient seawater are revealing new information about how oxygen rose in the Earth’s atmosphere more than 2 billion years ago.

And you thought your salt lamp was cool.

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Digging into a 1.9-kilometer-deep (1.2-mile) hole, researchers uncovered salt crystals left behind from evaporated seawater dating back 2 billion years. It changes what we know about how and when our atmosphere was created. The study is published in Science.

“It has been hard to test these ideas because we didn’t have evidence from that era to tell us about the composition of the atmosphere,” said Clara Blättler, a postdoctoral research fellow and first author of the study, in a statement.

That’s where the crystals, or mineral deposits, come in. Within them, scientists found a large amount of sulfate – a component of seawater that is created when sulfur reacts with oxygen – indicating oxygen began to show up in the Earth’s atmosphere between 2.4 and 2.3 billion years ago.

Until now, scientists weren’t sure whether this process took place over millions of years or occurred relatively quickly.

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“This is the strongest ever evidence that the ancient seawater from which those minerals precipitated had high sulfate concentrations reaching at least 30 percent of present-day oceanic sulfate as our estimations indicate,” said the study’s senior author Aivo Lepland. “This is much higher than previously thought and will require considerable rethinking of the magnitude of oxygenation of Earth’s 2-billion-year-old atmosphere-ocean system.”

It makes Earth’s “Great Oxidation Event” much more significant. Acting as a catalyst, the growth of cyanobacteria shifted the Earth's atmospheric and ocean chemistries through photosynthesis – the taking in of carbon dioxide and giving off of oxygen – somewhere between 2.5 and 1.6 billion years ago

According to the study, these deposits are more than a billion years older than any previously discovered. They also contain other deposits – such as halite, calcium, magnesium, and potassium – that normally dissolve easily, giving geologists a glimpse of how Earth’s oceans and atmosphere were composed at that time.  

Oxygen makes up about 20 percent of the air that we breathe and it goes without saying that it is essential for life as we know it. Now, we know that it appeared at a much quicker pace.  

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"Instead of a trickle, it was more like a fire hose," said Blättler. "It was a major change in the production of oxygen."


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