Scientists recently discovered the source of naturally occurring aerosol particles in Earth's atmosphere that play an important role in cloud formation. The particles in questions are known as 'climate-active organic aerosols,' and are vapors composed of large molecules that contain almost equal numbers of carbon, oxygen and hydrogen.

The international research team found that these vapors form shortly after the release of plant emissions into the air. The vapors condense on small particles, causing them to grow bigger and bigger. Eventually, they reach a size that is large enough to cause noticeable changes in the atmosphere - like reflecting sunlight, and acting as nuclei for cloud formation.

The research was published in the journal Nature, and shows a direct mechanism for how life on Earth can influence the production of particles that play a big role in processes affecting Earth's climate.

The study is useful for astrobiologists who are interested in the connections between Earth's biosphere and climate, and how climate change will affect the future habitability of our planet. But could studies like these also have implications in comparative planetology and the search for life beyond Earth?

As the new study shows, life on Earth can have a noticeable affect on the composition and behavior of our planet's atmosphere. There are now over 1,000 identified exoplanets in orbit around distant stars (and the number keeps growing). Scientists are now exploring techniques that could be used to study the atmospheres of these planets in detail. The ultimate goal is to find atmospheric biosignatures that would identify alien life.

Astrobiology Magazine spoke with Dr. Nancy Kiang of NASA's Goddard Institute for Space Studies about the prospect of using climate-active organic aerosols as a biosignature. Dr. Kiang is a specialist when it comes to the interactions between Earth's biosphere and atmosphere, and how these interactions could produce signs of life at global scales.

First off, plants themselves could provide biosignatures on an exoplanet. If you observe how light reflects off a planet's surface, and if that surface is covered by a lot of plants, you can actually 'see' the plants due to the way in which their chlorophyll absorbs light. This is a spectral signature known as the "vegetation red edge."

"Satellites can see this to identify where plants are on our planet," said Dr. Kiang. "If we were to see a feature like this on another planet, it would tell us that advanced life had evolved on land. At least 20 percent of the planet's surface would have to be covered with vegetation AND cloud-free for a strong enough signal for a telescope to see."

Dr. Kiang points out that the results of the new study could actually pose more problems for this type of direct detection of plants on another planet.

"The catch is that plants promote cloud formation through transpiration of soil moisture back to the atmosphere," said Dr. Kiang. "Thus vegetation can help its own persistence and even its spread through enhancing the availability of moisture."

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A Question of Atmospheres: On Earth and Beyond