An international team of researchers has developed a new technique for studying what could be described as a “fossilized atmosphere” preserved in micrometeorites—tiny particles that traveled through space before impacting ancient Earth.
Today, we witness similar dust streams in the form of shooting stars, but their ancient counterparts remain locked in rock layers dating back billions of years. A team led by the University of Göttingen, in collaboration with researchers from the Open University, the University of Pisa, and Leibniz University Hannover, has devised a new method for reconstructing the ancient atmosphere using these tiny particles of rock and metal. Their findings were recently published in a new study.
Fossilizing the Atmosphere
When micrometeorites fall to Earth, they interact with the atmosphere in specific ways. Metals like iron and nickel oxidize when they encounter Earth’s oxygen, while others melt during atmospheric entry. Some completely melt and reform as tiny spherical particles known as cosmic spherules. One important subtype of these is I-type cosmic spherules, in which all the oxygen found in the iron and nickel comes directly from Earth’s atmosphere at the time they fell.
Each year, immense quantities of these spherules fall to Earth, creating a chemical archive of atmospheric conditions at the time of their arrival. By extracting I-type cosmic spherules from sedimentary rock layers, scientists can reconstruct the triple oxygen isotope composition of ancient atmospheric O₂. This, in turn, helps estimate past CO₂ levels.
A New Method
The team’s work enables the precise analysis of the oxygen and iron isotopes in micrometeorites across different geological periods. By investigating the isotope ratios, the team can determine the early Earth’s atmospheric composition. From their results, the researchers were able to extrapolate further information about CO2 concentrations during the period and the growth of organic matter through photosynthesis.
Of the 100 samples in the study, 92 were new samples collected from six different sedimentary sites, and the remaining eight were sourced from existing collections. While the team successfully demonstrated the precision of their method in analyzing samples from the Carboniferous to Cretaceous periods, locating unaltered I-type samples poses a challenge for mainstreaming the technique.
The researchers found that even morphologically intact spherules can undergo some alterations over the large spans of time between their paleo-climatic formation and the present day. To mitigate inaccurate paleoclimate estimates, the team emphasizes the importance of rigorous sample screening.
Continuing to Investigate the Early Earth
The group’s work offers a new method for interrogating Earth’s distant past and understanding climate over large time scales. Modern concerns over CO2 concentrations leading to global warming make understanding the long-term context of climate change especially important.
“Our analyses show that intact micrometeorites can preserve reliable traces of isotopes over millions of years despite their microscopic size,” said lead author Dr Fabian Zahnow, formerly Doctoral Researcher at Göttingen University, now at the Ruhr University Bochum.
The team emphasizes that long-term geochemical processes must be carefully accounted for to ensure accurate reconstructions of early atmospheric conditions.
The paper “Traces of the Oxygen Isotope Composition of Ancient Air in Fossilized Cosmic Dust” appeared on July 23, 2025, in Communications Earth & Environment.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.