“Astronomers had concentrated only on vegetation before, but with a better color palette, researchers can now look beyond a half-billion years and up to 2.5 billion years back on Earth’s history to match like periods on exoplanets,” said Lisa Lisa Kaltenegger, Cornell University professor of astronomy and director of the Carl Sagan Institute. “If an alien had used color to observe if our Earth had life, that alien would see very different colors throughout our planet’s history – going back billions of years – when different life forms dominated Earth’s surface.”For the last half-billion years – roughly 10 percent of our planet’s lifetime – chlorophyll, present in many familiar forms of plant life such as leaves and lichen, has been the key component in Earth’s biosignature. But other flora, such as cyanobacteria and algae, are much older than land-based vegetation, but their chlorophyll-containing structures leave their own telltale signs on a planet’s surface.
“In our search to understand exoplanets, we’re using the early Earth and its biological milestones in history as a Rosetta stone,” said Jack O’Malley-James, a research associate at Cornell’s Carl Sagan Institute. “Scientists can observe surface biosignatures beyond vegetation on Earth-like exoplanets by using our own planet as the key for what to look for.”
O’Malley-James’s research focuses on using Earth as a template for exploring how life would interact with the atmospheres and surfaces of habitable exoplanets. This involves using Earth-like ecosystems as a basis for envisioning possible extraterrestrial biospheres by finding the overlaps between the environments life has adapted to on Earth (or to which evolutionary biology suggests that life could adapt given the right ‘push’) and the environments we predict for potentially habitable exoplanets. He then use these alien-but-familiar biospheres as components of climate or photochemistry models to simulate how less Earth-like life might be remotely detectable on specific, or hypothetical, exoplanets.
Using nature’s color palette from early Earth, Cornell University astronomers have created a cosmic “cheat sheet” in order to understand where discovered exoplanets may fall along their own evolutionary spectrum. O’Malley-James and Lisa Kaltenegger, professor of astronomy and director of the Carl Sagan Institute, co-authored “Expanding the Timeline for Earth’s Photosynthetic Red Edge Biosignature” published in the Astrophysical Journal.
O’Malley-James and Kaltenegger modeled spectra of Earth-like exoplanets with different surface organisms that use chlorophyll.
Lichens (a symbiotic fungal and photosynthetic partnership) may have colonized Earth’s land masses some 1.2 billion years ago and would have painted Earth in sage to mint green colors. This coverage would have generated a “nonvegetative” photosynthetic red-edge signature. A red-edge signature is the part of the spectrum that helps keep planets from getting burned by the sun.
“When we discover an exoplanet, this research gives us a much wider range to look back in time,” Kaltenegger said. “We extend the time that we can find surface biota from 500 million years (widespread land vegetation) to about 1 billion years ago with lichen and up to 2 or 3 billion years ago with cyanobacteria.”
The Daily Galaxy, Sam Cabot, via Cornell University