Methanogens, the oldest organisms on Earth, could be the ideal candidate for Martian life, according to a University of Arkansas Fayetteville study. They have been found to survive harsh conditions on Mars.

Researchers said that the organisms are non-photosynthetic and can grow without oxygen and nutrients, capable of surviving in sub-surface environments.

Methanogens are prominently found in wetlands including swamps, marshes, gut of cattle, termites and other herbivores, and dead and decaying matter among others. They use hydrogen (energy source) and carbon dioxide (carbon source) to metabolise, and produce methane gas.

For the study, researchers exposed two species of methane-producing bacteria - Methanothermobacter wolfeii and Methanobacterium formicicum - to Martian conditions. One of the two species is a hyperthermophile and the other is a thermophile.

The researchers found that both the species endured the Martian freeze-thaw cycles that are below the organisms' optimum growth temperatures: 37 degrees Celsius (98.6 degrees Fahrenheit) for M. formicicum and 55 degrees Celsius (131 degrees Fahrenheit) for M. wolfeii.

"The surface temperature on Mars varies widely, often ranging between minus 90 degrees Celsius and 27 degrees Celsius over one Martian day," said Rebecca Mickol, a doctoral student in space and planetary sciences, in a press release. "If any life were to exist on Mars right now, it would at least have to survive that temperature range. The survival of these two methanogen species, exposed to long-term freeze-thaw cycles, suggests methanogens could potentially inhabit the subsurface of Mars."

"The low temperature on Mars inhibited their growth, but they survived," Mickol said. "Once they got back to a warm temperature, they were able to grow and metabolise again."

Researchers said that Methanogens also found under the Greenland ice cap and in deep basaltic rock formations, may help scientists in searching for life on the Red Planet and to offer a possible explanation for methane in the Martian atmosphere.

A 2014 Georgia Institute of Technology study found evidence of salt water on the surface of Mars. Researchers suspect water to contain ferric sulfate, a common mineral on the Red Planet.

"In HiRISE images, we see them forming, elongating and then fading over time," researcher Lujendra Ojha said. "That's why they're called seasonal - they form and flow when the temperature is right."