Source: [astrobio.net]

“An origin of life is not the same as an origin of a biosphere—that’s an important distinction,” says David Grinspoon, planetary scientist, curator of astrobiology for the Denver Museum of Nature & Science, and the first Baruch S. Blumberg NASA-Library of Congress Chair in Astrobiology.

To illustrate the concept Grinspoon offers a simple analogy. Say you’re starting a camp fire. It’s easy to get it to spark up, but you have to tend it first or it may just die out. But then the fire reaches a critical moment when it catches on and becomes self-sustaining.

Grinspoon wonders: Did life start out like little sparks that are vulnerable to extinction? And did it, once it transitioned to a global phenomenon, become like a self-sustaining flame?

Grinspoon’s work focuses on the evolution of climate and atmosphere on Earth-like planets. At a recent conference themed Habitable Worlds Across Time and Space, held at the Space Telescope Science Institute in Baltimore, MD, he discussed the implications of this viewpoint for Earth’s nearest neighbors: Venus and Mars.