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Scientists use cosmic dust to reconstruct Earth's atmospheric history

Since the beginning of Earth's history, tiny particles of rock and metal from space have been hitting our planet. On clear nights, we can even see their traces as shooting stars. Trapped in layers of rock, these micrometeorites can remain preserved for billions of years.

An international research team led by the University of Göttingen and including the Open University, the University of Pisa, and Leibniz University Hannover has developed a method that allows them to reconstruct the atmosphere of the past using fossilized micrometeorites. The results were in Communications Earth & Environment.

When metallic micrometeorites from space enter Earth's atmosphere, they melt. In addition, iron and nickel oxidize on contact with oxygen in the air. These processes create microscopic spherical structures. They consist of oxide minerals whose oxygen comes from the atmosphere.

Countless numbers of them fall to Earth every year, where they are deposited. They offer great potential for drawing conclusions about the past, as their fossilized remains provide a preserved "chemical archive" of the atmosphere from the time of their formation.

The newly developed method allowed researchers at Göttingen University's Geoscience Center and the Leibniz University Hannover to determine the composition of oxygen and iron isotopes in tiny fossil micrometeorites from different geological periods with high precision for the first time. The ratios of different isotopes provide information about the isotopic composition of the early atmosphere. In addition, the data also allow conclusions to be drawn about CO₂ concentrations at that time and about the formation of organic matter around the world, mainly due to plants photosynthesizing.

The study shows that these tiny spheres are a promising addition to the usual methods used in geological climate research for reconstructing past CO₂ concentrations.

"Our analyses show that intact micrometeorites can preserve reliable traces of isotopes over millions of years despite their microscopic size," explains lead author Dr. Fabian Zahnow, formerly Doctoral Researcher at Göttingen University, now at the Ruhr University Bochum.

At the same time, it became clear that geochemical processes in soil and rock change micrometeorites after they have landed on Earth, meaning careful geochemical investigation is essential.