Uncovering Mysteries of Earth’s Primeval Atmosphere 4.5 Billion Years Ago and the Emergence of Life

An artistic illustration of Earth today and 4.5 billion years ago.
Credit: Tobias Stierli / NCCR PlanetS

A team of international scientists led by ETH researcher Paolo Sossi has gained new insights into Earth’s atmosphere of 4.5 billion years ago. Their results have implications for the possible origins of life on Earth.

Four-​and-a-half billion years ago, Earth would have been hard to recognize. Instead of the forests, mountains, and oceans that we know today, the surface of our planet was covered entirely by magma – the molten rocky material that emerges when volcanoes erupt. This much the scientific community agrees on. What is less clear is what the atmosphere at the time was like. New international research efforts led by Paolo Sossi, senior research fellow at ETH Zurich and the NCCR PlanetS, attempt to lift some of the mysteries of Earth’s primeval atmosphere. The findings were published today in the journal Science Advances.

Making magma in the laboratory

“Four-​and-a-half billion years ago, the magma constantly exchanged gases with the overlying atmosphere,” Sossi begins to explain. “The air and the magma influenced each other. So, you can learn about one from the other.”

To learn about Earth’s primeval atmosphere, which was very different from what it is today, the researchers therefore created their own magma in the laboratory. They did so by mixing a powder that matched the composition of Earth’s molten mantle and heating it. What sounds straightforward required the latest technological advances, as Sossi points out: “The composition of our mantle-​like powder made it difficult to melt – we needed very high temperatures of around 2,000° Celsius.”

That required a special furnace, which was heated by a laser and within which the researchers could levitate the magma by letting streams of gas mixtures flow around it. These gas mixtures were plausible candidates for the primeval atmosphere that, as 4.5 billion years ago, influenced the magma. Thus, with each mixture of gases that flowed around the sample, the magma turned out a little different.

“The key difference we looked for was how oxidized the iron within the magma became,” Sossi explains. In less accurate words: how rusty. When iron meets oxygen, it oxidizes and turns into what we commonly refer to as rust. Thus, when the gas mixture that the scientists blew over their magma contained a lot of oxygen, the iron within the magma became more oxidized.

This level of iron oxidation in the cooled-​down magma gave Sossi and his colleagues something that they could compare to naturally occurring rocks that make up Earth’s mantle today – so-​called peridotites. The iron oxidation in these rocks still has the influence of the primeval atmosphere imprinted within it. Comparing the natural peridotites and the ones from the lab therefore gave the scientists clues about which of their gas mixtures came closest to Earth’s primeval atmosphere.

A new view of the emergence of life

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