Yet, some of the most promising locations to search for ancient life on Mars are places where water may have been in contact with volcanic rocks, ancient hydrothermal systems where conditions may have been conducive to life.

CNN: How the search for aliens can help sustain life on Earth

Rocks initially formed as layers of sediment laid down in an ancient sea can be deciphered by knowing that older layers are found beneath the younger layers.

BBC: Mars south pole

The twin landers, each the size of a desk and weighing 375 pounds (170 kilograms), will ramble dozens of meters a day, drilling into rocks and scooping up soil in preliminary field studies to help identify ancient oases.

CNN: Race to Mars begins a distant search for life