Scientists have discovered evidence of ancient wet-dry cycles on Mars, which may have facilitated the emergence of life.
The findings were published in a recent paper in the journal Nature and are based on data from NASA's Curiosity Mars rover.
Explorers have found a well-preserved ancient mud crack with a distinctive hexagonal pattern. These cracks are believed to be the first evidence of a dry-wet cycle in early March.
These cycles are thought to have played an important role in the formation of life on Earth by helping to assemble the complex chemical elements required for microbial life. Lead author of the paper, William Rapin of France's Institute of Astrophysics and Planetology, said: "These distinctive mud cracks form when wet and dry conditions occur over and over again. - probably seasonal.
The discovery was made in the transition zone between a clay-rich layer and a top layer rich in salty minerals called sulfates. As the mud dries, it shrinks and breaks, forming T-shaped joints.
However, frequent exposure to water caused these joints to soften and form a Y-shape, eventually forming a hexagon.
Hexagonal cracks in the transition zone continued to form even as new sediments were deposited, indicating that wet and dry conditions continued for a long time. A sulfate crust along the edges of the crack, confirmed by Curiosity's precision laser instrument, ChemCam, made the mud cracks resistant to erosion, preserving them for billions of years.
"This is the first solid evidence we've seen that the ancient climate of Mars had a regular cycle of dry and wet like Earth," Rapin said. "But even more importantly, the wet-dry cycles are useful - maybe even necessary - for the molecular evolution that could lead to life."
Although water is essential to life, a careful balance is required. The wet-dry cycle controls the concentration of chemicals that fuel the basic reactions that lead to the formation of polymers, the long chains of carbon-based molecules believed to be the chemical building blocks of life.
The discovery of the Pontours mud fissures may have given scientists the first opportunity to study the remains of the cauldron of life. Unlike Earth, Mars has no tectonic plates so much of the planet's older history is still preserved.
"We're pretty lucky to have a planet like Mars nearby that still remembers the natural processes that could lead to life," Rapin said.
