How do scientists know that early Mars may have supported life?

Scientists have long investigated whether early Mars could have supported life, primarily by searching for evidence of conditions that would allow for the persistence of liquid water, which is considered essential for life.1

The scientific view that early Mars may have been hospitable is supported by several key factors:

• Earth-like Conditions: There is compelling evidence that conditions on early Mars were similar to those on Earth during the period when life first arose on our planet.1
• Liquid Water: The search for life has focused on identifying evidence of warm conditions that would enable liquid water to exist. While the surface of Mars is currently very dry, there is evidence that liquid water may have flowed on the surface in the past and, in some places, may still flow intermittently.12
• Biological Resilience: Recognition that life on Earth can survive in extreme environments—such as deep-sea vents, acidic conditions, and deep within rocks—has expanded the range of environments scientists consider potentially habitable.1
• Material Exchange: Scientists recognize that Earth and Mars have exchanged materials via meteorites, raising the possibility that life could have been transported between the two planets.1

While some past claims of finding microbial fossils in Martian meteorites were highly publicized, the scientific consensus is that these findings likely have abiological explanations.132