It took a long time for atmospheric evidence of life to accumulate in Earth's atmosphere. We need to heed that fact in the search for life.
This view of Earth from space is a fusion of science and art, drawing on data from multiple satellite missions and the talents of NASA scientists and graphic artists. This image originally appeared in the NASA Earth Observatory story Twin Blue Marbles. Image Credits: NASA images by Reto Stöckli, based on data from NASA and NOAA.
When Earth formed about 4.5 billion years ago, its atmosphere was nothing like it is today. At that time, the atmosphere and oceans were anoxic. About 2.4 billion years ago, free oxygen began to accumulate in the atmosphere during the, one of the defining periods in Earth’s history. But the oxygen came from life itself, meaning life was present when the Earth’s atmosphere was much different.
It’s not just life that’s changed over time. Plate tectonics have changed and may have been ‘stagnant lid’ tectonics for a long time. In stagnant lid tectonics, plates don’t move horizontally. That can have consequences for atmospheric chemistry. The authors outline what they say are the most important lessons that the early Earth can teach us about the search for life.
Earth’s history is written in chemical reactions. This figure from the research shows the percentage of sulphur isotope fractionation in sediments. The sulphur signature disappeared after the GOE because the oxygen in the atmosphere formed an ozone shield. That blocked UV radiation, which stopped sulphur dioxide photolysis. “Anoxic planets where O2 production never occurs are more likely to resemble the early Earth prior to the GOE,” the authors explain. Image Credit: Stüeken et al. 2024.
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