In recent years, scientists have been exploring the possibility that early Earth may have been a purple planet. This theory is based on the discovery of purple archaea, which used a molecule called retinal to photosynthesize before oxygen became abundant on the planet. A study from 2018 expanded on this idea, suggesting that there may have been other potential life forms on Earth in its early days.
One of the authors of this paper was Shiladitya DesSarma, a molecular biologist at the University of Maryland. To test this theory, researchers collected spectral data on 20 species of purple bacteria 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 were able to create a collection of light signatures.
This information is now part of an ongoing database that is publicly available for other researchers to use in their own projects. Astronomers can use biosignatures, such as the color of a planet’s surface, to search for signs of life on other planets. 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 when discussing the search for extraterrestrial life.