Purple may have been the color of early Earth, according to scientists who believe that purple bacteria used a molecule called retinal to photosynthesize before the planet was filled with oxygen. This theory was put forth in a 2018 study by Shiladitya DesSarma, a molecular biologist at the University of Maryland.
Recent research has expanded on potential life forms that could have existed on Earth in its early days, including purple bacteria collected from various environments like marshes and deep-sea hydrothermal vents. By measuring the wavelengths of light these bacteria reflect and modeling how these patterns may appear on a distant planet, scientists have created a collection of light signatures that is now part of an ongoing database publicly available for other researchers to use in their own projects.
Astronomers search for signs of life on other planets using biosignatures, such as the color of a planet’s surface. Reflected light spectroscopy is often used for this purpose but current telescopes are limited in their capabilities. For example, the James Webb Space Telescope can only detect biosignatures in an exoplanet’s atmosphere and cannot measure reflected light from the planet’s surface. Edward Schwieterman, an astronomer at the University of California Riverside emphasizes this limitation.