Scientists are sure that Mars once had an atmosphere and liquid water on its surface. Scientists have known since very early in the mission of Curiosity in 2012 that Gale Crater once contained lakes. The image below shows a feature found on Mars called desiccation cracks which form when mud is exposed to air, dries, and cracks.
Scientists say that we see this same phenomenon on Earth. The mudcracks found in Gayle Crater prove that the lakes in Gale crater many years ago went through the same cycles we see on Earth. Scientists first discovered the desiccation cracks in Gale Crater in early 2017.
Further analysis has now confirmed that the features are indeed desiccation cracks. The study indicates that the location of the desiccation cracks nearer the center of the ancient lake bed than the edge suggests that lake levels rose and fell dramatically over time.
The scientists specifically looked at a slab of rock about the size of a coffee table called “Old Soaker” that has patterns on its surface identical to desiccation features found on Earth. The scientists studied the rock using the Mastcam, Mars Hand Lens Imager, ChemCam Laser Induced Breakdown Spectrometer (LIBS), and Alpha-Particle X-Ray Spectrometer (APXS) instruments on the Curiosity rover. That look proved that the polygons in the structure of Old Soaker are confined to a single layer of rock and with sediments filling cracks between them.
These formed from exposure to air and not mechanics like thermal or hydraulic fracturing. These cracks are direct evidence of drying on Mars and contribute to the understanding of Mars’ ancient climate.