Gasses From Ancient Earth Hide Key to Discovering Alien Life
While the hunt for signs of life in other worlds continues, researchers rely on certain biosignatures to confirm that a planet is, or once was, able to sustain life. The presence of water, oxygen, and carbon dioxide for example, combine to create a biosignature that supports life.
"Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life," reads the study's abstract. "However, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic Archean [era] or less oxic Proterozoic [era] eons are unknown."
Still, we know that photosynthesis and life can flourish without the presence of much oxygen. Theough Earth didn't have much oxygen during the Archaean period—from 4 to 2.5 billion years ago—and the Proterozoic period, which ended 500 million years ago, microbial life was certainly around. In such instances, scientists suggested that we look for biosignatures involving other comibations of gasses contained in the atmosphere of early Earth like methane, nitrogen, water and carbon dioxide.
"Given current knowledge of the evolution of the atmosphere since the Archean, we calculate that Earth's atmosphere has been in thermodynamic chemical disequilibrium since the early Archean as a result of life," the study concludes. "The magnitude of this disequilibrium has increased through time, correlated with increases in atmospheric oxygen and probable growth in biomass. The contributions to disequilibrium from solid states of matter were not included in these calculations because our focus is on properties that would be remotely detectable on exoplanets in the future."
While other researchers are searching for life on other planets using a "sniff test" that detects for the presence of such materials on exoplanets using spectroscopy, the WFIRST telescope, the Very Large Telescope, and the soon-to-launch James Webb telescope, this new research suggests that those tools also ought to be looking for carbon monoxide, as most biological processes that creates both methane and carbon dioxide cannot create carbon monoxide, too.
"Life everywhere has to obey the same rules of physics and chemistry—it has to make a living in its environment," says lead study author Joshua Krissansen-Totton. "It has to use the energy that's available, so producing methane isn't such an unlikely thing."