Researchers have discovered ancient gases and liquids trapped in 1.4-billion-year-old halite crystals from northern Ontario, Canada. Their analyzes directly limit Mesoproterozoic (1.8–0.8 billion years ago) concentrations of oxygen and carbon dioxide to 3.7% of modern levels and 10 times pre-industrial levels, respectively. The results suggest that this was a period of even climate and that atmospheric oxygen concentrations, at least temporarily, exceeded the metabolic needs of early animals long before their appearance.
Examples of photographs of primary, mixed and secondary halite inclusion complexes. Image credit: Park etc.., doi: 10.1073/pnas.2513030122.
Scientists have long known that liquid inclusions in halite crystals contain samples of Earth's early atmosphere.
But getting accurate measurements of these inclusions has proven challenging: they contain both air bubbles and brine, and gases such as oxygen and carbon dioxide behave differently in water than in air.
“It’s an incredible feeling to discover a sample of air that is a billion years older than the dinosaurs,” said Rensselaer Polytechnic Institute graduate student Justin Park.
“The carbon dioxide measurements we obtained had never been done before,” said Rensselaer Polytechnic Institute professor Morgan Schaller.
“We have never been able to peer into this era of Earth's history with such precision. These are real samples of ancient air!”
The results show that the Mesoproterozoic atmosphere contained 3.7% more oxygen than today. This is a surprisingly large amount, high enough to support complex multicellular animal life that did not emerge until hundreds of millions of years later.
Meanwhile, there was 10 times more carbon dioxide than today—enough to counteract the “dim young Sun” and create a climate condition similar to today.
One question naturally arises: if there was enough oxygen to keep animals alive, why did it take so long to finally evolve?
“The sample is just a snapshot of geologic time,” Park said.
“This may reflect a short-lived, transient oxygenation event in this long era that geologists jokingly call the “Boring Billion.”
“This was an era in Earth's history marked by low oxygen levels, widespread atmospheric and geological stability, and scant evolutionary change.”
“Despite the 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.”
Previous indirect estimates of carbon dioxide during this period indicated lower levels, inconsistent with other observations showing that there were no significant glaciers during the Mesoproterozoic era.
The team's direct measurements of high levels of carbon dioxide, combined with temperature estimates from the salt itself, suggest that the Mesoproterozoic climate was milder than previously thought—comparable to today's.
“Ted algae emerged around this point in Earth's history and today they continue to make a significant contribution to global oxygen production,” Professor Schaller said.
“The relatively high oxygen levels may be a direct result of the increasing abundance and complexity of algae life.”
“Perhaps what we captured is actually a very exciting moment in the middle of Boring Billion.”
teams paper was published today in the magazine Proceedings of the National Academy of Sciences.
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Justin J. Park etc.. 2025. Breathe life into a boring billion: direct constraints from 1.4 Ga fluid inclusions indicate a favorable climate and an oxygen-rich atmosphere. PNAS 122 (52): e2513030122; doi: 10.1073/pnas.2513030122
