NASA/JPL/Space Science Institute

ScienceShot: An Atmospheric Flip-Flop

About 2.45 billion years ago, Earth might have been confused for Titan. Research published today in Nature Geoscience suggests that our planet had the same hazy, methane-rich atmosphere as Saturn's largest moon (pictured). Scientists analyzed 2.65-billion- to 2.5-billion-year-old sediments from South Africa in order to reconstruct past ocean and atmosphere chemistry. They were surprised to find that, rather than a single, consistent past atmospheric state, Earth flip-flopped between "organic haze," or hydrocarbon smog, and "haze-free" conditions. Methane-producing microbes in the ocean, the researchers say, drove these cycles. Some oxygen was being produced by other seafaring microbes, but little of it reached the atmosphere. It was not until about 100 million years later that photosynthetic organisms known as cyanobacteria dominated the seas and injected massive amounts of oxygen into the atmosphere, creating conditions similar to those we enjoy today.

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