Astronomers Want to Find the Habitable Planet Where Alien First Life

This line of thought can be extended to many other properties of the atmosphere. Living things also emit large amounts of methane, a greenhouse gas that helps keep our planet warm.  

Extensive forest canopies alter the amount of sunlight reflected off the surface, also affecting the temperature of our world. Even the production of various gaseous byproducts from creatures large and small can change the air pressure of planet Earth's atmosphere.

The earliest possible signs of life on our world in the fossil record suggest that life may have emerged when parts of our planet were still liquid.  It must have been a very hostile place. But billions of years later, that's pretty good.

The authors of the new paper envision a world at the edge of the habitable zone, either almost too cold or almost too hot.

But if alien life managed to start there, it would have the opportunity to improve the makeup of the planet, perhaps by raising or lowering atmospheric pressure or temperature, or by creating recesses underground where life could thrive. Therefore, we must rethink the traditional definition of the habitable zone.