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Artist's impression of haze on Earth during the Archean Eon. | Francis Reddy/NASA's Goddard Space Flight Center
Earth

Study of Ancient Ocean Temperatures Shows Sudden Cooling That Let Life Evolve

Such a dramatic cooling is hard to fathom, emphasizing how scientists need to remember how different conditions were in the past when figuring out how life evolved over time.

The image on the left depicts what Earth might have looked like more than 3 billion years ago in the early Archean. The orange shapes represent the magnesium-rich proto-continents before plate tectonics started, although it is impossible to determine their precise shapes and locations. The ocean appears green due to a high amount of iron ions in the water at that time. The timeline traces the transition from a magnesium-rich upper continental crust to a magnesium-poor upper continental crust. | Ming Tang/University of Maryland
Microbial reefs called stromatolites are examples of biological structures found as far back as 3.7 billion years ago. | Pamela Reid, Ph.D., University of Miami Rosenstiel School of Marine and Atmospheric Science