Scientists extract ancient air from rock-salt time capsule
- Scientists extracted 1.4-billion-year-old air trapped in rock salt, providing a rare sample of Earth’s ancient atmosphere.
- The air contained higher oxygen and carbon dioxide levels than scientists expected, suggesting a warmer, moderate climate.
- These findings help explain how early Earth supported life during the so-called “Boring Billion” years.
This ancient air sample is 1.4 billion years old
Ancient Earth, 1.4 billion years ago, was a very different place. Land masses clustered together to form a supercontinent called Nuna. Meanwhile, life on our planet was primarily bacteria. On December 22, 2025, scientists from the Rensselaer Polytechnic Institute in Troy, New York, said they recovered a pristine sample of the atmosphere from this time period. The team extracted and analyzed air that had been trapped in halite crystals, also known as rock salt. They discovered higher oxygen and carbon dioxide levels in the atmosphere than they expected. Plus, their research showed Earth had a moderate climate during that time.
Lead author Justin Park of the Rensselaer Polytechnic Institute said:
It’s an incredible feeling, to crack open a sample of air that’s a billion years older than the dinosaurs.
Co-author Morgan Schaller of the Rensselaer Polytechnic Institute added:
The carbon dioxide measurements Justin obtained have never been done before. We’ve never been able to peer back into this era of the Earth’s history with this degree of accuracy. These are actual samples of ancient air!
The researchers published their study in the peer-reviewed journal Proceedings of the National Academy of Sciences on December 22, 2025.
Studying ancient air bubbles
For decades, scientists have directly studied Earth’s ancient atmosphere by analyzing tiny air bubbles trapped in old ice from Antarctica and Greenland. The air bubbles provide valuable information about atmospheric conditions, including oxygen and carbon dioxide levels. But the age of the ice limits how far back in time researchers can go. Most ancient ice samples are hundreds of thousands of years old, with the oldest sample dated at six million years.
However, as demonstrated in this new study, scientists can now extract even older air samples from ancient rock salt, also known as halite. They used samples that were deep in the ground and recovered using a core drill.
The researchers said the mineral originated in a shallow basin that once held a subtropical lake. Under the glare of the sun, that lake water evaporated. And as the water evaporated, it formed a brine. Eventually, the brine crystallized into halite, with some liquid getting trapped inside the crystals. Suspended in the fluid were air bubbles, which held a record of Earth’s early atmosphere.
Then, sediment covered the crystals. Over time – 1.4 billion years – the continents shifted, moving the site holding ancient halite crystals to present-day northern Ontario, Canada. Remarkably, those crystals did not undergo significant transformation, or metamorphosis, due to compression and heat. As a result, the air bubbles and brine were preserved in the halite.
Scientists had known for some time that these air bubbles existed in halite. But they had trouble analyzing the gases in those bubbles because of the way oxygen and carbon dioxide dissolve in brine. However, for this study, Park, Schaller and their team were able to overcome that problem with specialized equipment and analysis techniques.
Oxygen in the atmosphere 1.4 billion years ago
Life on Earth during the Mesoproterozoic Era (1.8 to 0.8 billion years ago) was mostly microbial life. Red algae had just started to appear and would become, to this day, a major producer of oxygen. However, the first complex multicellular organisms – the first animals and plants – would not emerge till 800 million years later.
The researchers expected low levels of oxygen in the atmosphere 1.4 billion years ago. Instead, they were surprised by unexpectedly higher values, at 3.7% of current levels. (Today, oxygen makes up 21% of our atmosphere.) Even though that level is still low compared to today, it could have supported complex multicellular life.
That left the scientists with a puzzle: if oxygen levels were that high, why did it take 800 million years for complex life forms to emerge?
Carbon dioxide and the faint sun paradox
In addition, the researchers found higher-than-expected levels of carbon dioxide, 10 times that of preindustrial levels. And that finding may solve a puzzle called the faint sun paradox.
According to a widely accepted model of the sun’s evolution, our star only emitted 70% of its current flux during Earth’s early history. Therefore, Earth’s climate should have been cold, causing glaciers to form. However, geological evidence shows that 1.4 billion years ago, there were no glaciers; instead, liquid water sustained microbial life.
Why was the Earth warm if the sun emitted less heat? The high level of carbon dioxide in the atmosphere, the researchers think, was enough to cause a greenhouse effect that warmed the Earth during a time when the sun’s output was just 70% of current levels.
Ancient air in halite crystals points to a moderate climate
The Mesoproterozoic occurred during a stretch of time scientists call the Boring Billion, because there was not much biological evolution, no glacial activity and little change in the atmosphere.
Park commented:
Despite its name, having direct observational data from this period is incredibly important because it helps us better understand how complex life arose on the planet, and how our atmosphere came to be what it is today.
The team’s analysis indicates that the Mesoproterozoic climate was milder than previous studies had suggested. Or was their result an anomaly?
Park cautioned that the sample they analyzed was a very brief snapshot of the atmosphere during the Mesoproterozoic Era:
It may reflect a brief, transient oxygenation event in this long era that geologists jokingly call the ‘Boring Billion.’
Schaller also suggested:
It’s possible that what we captured is actually a very exciting moment smack in the middle of the Boring Billion.
Bottom line: Scientists extracted ancient air from 1.4-billion-year-old halite crystals. It contained higher atmospheric oxygen and carbon dioxide levels than expected.
Via Rensselaer Polytechnic Institute
Read more: Study suggests early Earth’s atmosphere was rich in carbon dioxide
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