"Using light-capturing proteins in living microbes, scientists have reconstructed what life was like for some of Earth’s earliest organisms. These efforts could help us recognize signs of life on other planets, whose atmospheres may more closely resemble our pre-oxygen planet. 

The earliest living things, including bacteria and single-celled organisms called archaea, inhabited a primarily oceanic planet without an ozone layer to protect them from the sun’s radiation. These microbes evolved rhodopsins — proteins with the ability to turn sunlight into energy, using them to power cellular processes."

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