The green sands were discovered in Lake Jezero Crater, an ancient dry lake that was part of a rich river system at a time when Mars had liquid water, air and a magnetic field. Scientists expected to find sedimentary layers at the bottom of the lake, but they saw igneous rocks exposed due to water erosion. These greenish rocks are made up of large grains of olivine, a dirtier version of peridot that turns many Hawaiian beaches a deep green.
These rocks are regarding 4 billion years old, and they are very similar to the igneous rocks on Earth at the beginning of its existence. On our planet, such stones have long disappeared, so it is impossible to find out under what conditions life on Earth originated. But Mars is a real laboratory for studying the early solar system. Understanding the evolution and history of rocks on Mars might help figure out how life might have arisen on Mars and how that compares to early life and conditions on ancient Earth. The search for life is one of the main goals of Perseverance. Understanding how and under what conditions life began on Earth will help scientists know where to look for it on other planets and moons.