Humanity has not yet discovered traces of life outside the Earth. Today we do not yet have the technology that would allow us to accurately detect living organisms or plants on distant planets. But if there is life on them, it must necessarily affect the atmosphere of the planet. But how exactly? New studies of the composition of the young Earth's atmosphere will help find the answer.
One way to find traces of life on exoplanets is to look for large amounts of oxygen, which can be detected using spectroscopy. There are not many ways to produce oxygen without photosynthesis. However, it is now known that a planet's atmosphere does not have to have a high level of oxygen, even if it contains life.
The study of the ancient Earth makes us understand that between the Archean and Proterozoic periods (4-2.5 billion years ago), our planet did not have a high level of oxygen. Nevertheless, hordes of microorganisms already lived on our planet.
“An oxygen-rich atmosphere can be quite rare,” says Joshua Krissansen-Totton of the University of Washington in Seattle. "Even if you travel to any period of history, you may not find the amount of oxygen in the atmosphere we are used to, so we should not bet on it alone when looking for extraterrestrial life."
Methane clouds
Astrobiologists have suggested that you can look for combinations of different gases that could coexist for decades if something living was constantly replenishing the reserves of these gases.
To understand the exact combination to look for, Chrisssensen-Totton and his colleagues calculated which gases were predominant in Earth's early atmosphere and how they might interact.
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They found that methane, nitrogen, water and carbon dioxide could be early signs of organic life. “These four elements cannot coexist together - they had to react with each other and destroy the methane,” explains Chrisssensen-Totton. "However, during the Young Earth period, most of the methane was released by microbes, and therefore it did not disappear."
The very process of methane production by living microorganisms is much simpler than the production of oxygen, which means that this phenomenon is much more common in the Universe and, therefore, it is easier to detect it.
New Horizons
A similar task of searching for mixtures of gases on distant exoplanets is just right for NASA's new telescope named after James Webb Space Telescope. It is set to launch in 2019 and will be able to study exoplanet atmospheres more closely than its predecessors.
According to Chrisssensen-Totton, even if life on other planets is radically different from Earth's, it will most likely release methane, which will serve as a beacon for us. “Life, wherever it is, obeys the same laws of physics and chemistry, so the production of methane is not such an unlikely thing,” - explains the scientist.