What are the characteristics of the earth’s atmosphere in the hot youth of our planet? Laboratory experiments with molten rock and gases have now provided insights into this question. 4.5 billion years ago, an atmosphere similar to that of Venus was created over the then magma ocean. The fact that the earth’s atmosphere developed differently than on our neighboring planet and ultimately made conditions more friendly to life has to do with the greater distance to the sun, the scientists explain.
Where oceans, mountains and lush landscapes characterize the earth’s surface today, there was once nothing but boiling embers: four and a half billion years ago our planet was completely covered by molten rock material that only emerges from volcanoes today. This original state of the earth’s surface is scientifically proven, but it is unclear what was about it. An international team of researchers headed by the Swiss Federal Institute of Technology in Zurich has now devoted itself to researching the primordial atmosphere by simulating the possible conditions on primeval earth. “4.5 billion years ago, magma was constantly exchanging gases with the atmosphere,” explains first author Paolo Sossi from ETH Zurich. “The air and the magma influenced each other. If you examine one, you also learn something about the other, ”says the scientist.
Floating laboratory magma
To enable conclusions to be drawn about the primordial atmosphere of the earth, he and his colleagues produced their own magma in the laboratory. To do this, they created a mixture that corresponds to the composition of the earth’s jacket material and heated the powder to a glowing liquid state. In order to give the material the necessary 2000 degrees Celsius and to be able to bring it into contact with gases, the scientists used ingenious technology: the powder was heated in a special oven by laser beams. In doing so, the researchers let the glowing lump float using what is known as aerodynamic levitation: the laboratory magma danced on a targeted stream of gases, as it were. These are mixtures, the composition of which represented different possible versions of the primordial atmosphere.
As the researchers explain, the effects of the gas mixtures on the magma allowed conclusions to be drawn about the composition of the atmosphere 4.5 billion years ago. “We were particularly interested in the effects on iron in magma. Because when iron meets oxygen, it oxidizes and turns into what we commonly call rust, ”says Sossi. If the gas mixture in the furnace contained a lot of oxygen, the iron in the magma was correspondingly more oxidized, the scientist explains.
After the samples had cooled, the researchers were able to examine how much the iron had been oxidized, depending on the composition of the gas mixture. They then compared the data obtained with analysis results from so-called peridotites. These are rocks of today’s mantle that date back to 4.5 billion years ago. They therefore formed under the influence of the atmosphere at the time.
Similar to today’s Venus
“We found that after cooling down from the initial magma state, the young earth had an only slightly oxidizing atmosphere with carbon dioxide as the main component, as well as nitrogen and some water,” reports Sossi. The results also showed that the surface pressure then was almost a hundred times higher than it is today. Due to the hot surface, the atmosphere probably expanded to far greater heights. With these features, the primeval gas envelope of our planet was much more similar to that of today’s Venus than the Earth’s atmosphere today, the scientists sum up.
The results thus again show that the earth and Venus had quite similar characteristics in their initial phases. But the sister planets developed differently: Due to its closer proximity to the sun and the associated higher temperatures, above all, Venus was unable to hold water for a long time and eventually lost it into space. The earth, however, was able to secure its liquid treasure. This in turn had an impact on the further development of the earth’s atmosphere: the oceans absorbed a large part of the carbon dioxide and thereby considerably reduced its content in the air. Ultimately, this developed the atmospheric conditions that made life possible and that still shape our blue planet today.
Source: Swiss Federal Institute of Technology Zurich, specialist article: Science Advances, doi: 10.1126 / sciadv.abd1387