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Scientists have reconstructed the conditions under which the earliest organisms on Earth must have existed, in what could be a major breakthrough for the study of life on other planets. Reconstitution is accomplished using light-harvesting proteins in living microorganisms. The earliest forms of life on Earth, including bacteria and single-celled organisms called archaea, inhabited a mostly oceanic planet to protect themselves from solar in the absence of an ozone layer. Early microbes developed rhodopsins, proteins capable of converting sunlight into energy using them to power cellular processes.

“Energy sources were probably very scarce on the early Earth. Bacteria and archaea figured out how to harness the abundant energy from the sun without the complex biomolecules needed for photosynthesis,” says Edward Schwieterman.

In the study, the scientists used artificial intelligence to analyze the sequence of rhodopsin and its evolution over time. A family tree was then created that allowed the researchers to reconstruct the proteins from 2.5 to 4 billion years ago, and the conditions that life might have faced when it first arose on Earth.

Unlike modern versions, which absorb blue, green, yellow, and orange light, ancient rhodopsins were tuned to absorb primarily blue and green light for reconstruction. The colors were chosen because early microbes lived in water to protect themselves from the sun. Since blue and green light penetrate water best, the earliest rhodopsins likely absorbed primarily these colors.

More 2 years ago, when oxygen levels in Earth’s atmosphere began to rise after the Great Oxygenation Event, rhodopsins evolved to absorb more colors of light.

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They are now able to absorb colors of light that the chlorophyll pigments in plants cannot. “This suggests co-evolution, as one group of organisms is utilizing light that is not absorbed the other. This could be because rhodopsin develops first and shields green light, so chlorophyll develops later and absorbs the rest. Or it could develop in reverse way,” said Dr. Schwieterman.

In future studies, the scientists hope to use synthetic biology techniques to resurrect the model rhodopsin in the lab.

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By Rebecca French

Rebecca French writes books about Technology and smartwatches. Her books have received starred reviews in Technology Shout, Publishers Weekly, Library Journal, and Booklist. She is a New York Times and a USA Today Bestseller...