LIFE × ATMOSPHERE
The First Methanogens
~3.46 billion years ago
Methanogens are microbes that live on hydrogen and carbon dioxide alone and release methane, and they may have formed an early biosphere about 3.46 billion years ago.
Methanogens are microbes that live on hydrogen and carbon dioxide alone and release methane. This metabolism, the set of chemical reactions that keep them alive, is called hydrogenotrophic methanogenesis and is among the simplest known. It requires no light, no oxygen and no organic matter, which makes methanogens plausible candidates for an early biosphere. The biosphere is the whole of the living things on a planet. Australian rocks three and a half billion years old contain trapped bubbles of methane. This methane has the isotopic signature of biological production, a proportion of light and heavy carbon atoms that living cells produce.
Why it matters
The methane of methanogens is one of the principal explanations for a temperate climate on the early Earth, under a Sun a fifth less luminous than today. On that hypothesis, microscopic organisms were already involved in setting the temperature of the planet.
Dating & uncertaintyDisputed
Methane enclosed in hydrothermal minerals 3.46 billion years old has a carbon signature that, as far as is known, only life produces. Hydrothermal minerals are deposited by circulating hot water. Researchers have also used molecular clocks, which estimate dates from differences between genes, to place methanogens earlier still. Roger and Susko (2018) object that these dates reflect the assumptions of the method more than the data.
Earth history as one day
05:42:3318 h 17 min before midnight
if Earth’s 4.54 billion years were compressed into a single day