ATMOSPHERE × CLIMATE

A Sky Full of Methane

~3.5 to 2.4 billion years ago

Archean · Paleoarchean

For a billion years the air contained no oxygen, and a great deal of methane. The methane came from microbes, and it trapped heat far better than carbon dioxide, keeping the surface warm under a Sun that shone a fifth more weakly than today. High above drifted an orange haze of organic particles, thickening and clearing as the methane rose and fell.

Why it matters

Here is the leading answer to the oldest puzzle in Earth science. The young Sun was too faint to keep the oceans liquid, and they stayed liquid regardless. Part of the answer is that life was warming its own planet.

Dating & uncertainty

That the Sun shone 20 to 25 percent more weakly is not in doubt, nor that the rocks record liquid water throughout. Which gas made up the difference is modelled rather than measured: methane, carbon dioxide and the haze itself all have advocates, and changing their proportions changes the answer.

Sources

1. Catling & Zahnle (2020), Science Advances · The Archean atmosphere
2. Feulner (2012), Reviews of Geophysics · The faint young Sun problem
3. Ozaki et al. (2017), Nature Geoscience · Effects of primitive photosynthesis on Earth's early climate system

Earth history as one day

05:29:5218 h 30 min before midnight

if Earth’s 4.54 billion years were compressed into a single day