Science, Tech, Math › Science Ancient Mars Rocks Show Evidence of Water Share Flipboard Email Print Science Astronomy Solar System An Introduction to Astronomy Important Astronomers Stars, Planets, and Galaxies Space Exploration Chemistry Biology Physics Geology Weather & Climate By Carolyn Collins Petersen Astronomy Expert M.S., Journalism and Mass Communications, University of Colorado - Boulder B.S., Education, University of Colorado Carolyn Collins Petersen is an astronomy expert and the author of seven books on space science. She previously worked on a Hubble Space Telescope instrument team. our editorial process Facebook Facebook Carolyn Collins Petersen Updated January 13, 2020 Imagine if you could explore Mars as it was some 3.8 billion years ago. That's about the time life was just starting on Earth. On ancient Mars, you could have waded through oceans and lakes and across rivers and streams. Was there life in those waters? A good question. We still don't know. That's because much of the water on ancient Mars disappeared. Either it was lost to space or is now locked underground and in the polar ice caps. Mars has changed incredibly in the past few billion years! What happened to Mars? Why doesn't it have flowing water today? Those are big questions that the Mars rovers and orbiters were sent to answer. Future human missions will also sift through the dusty soil and drill beneath the surface for answers. For now, planetary scientists are looking at such characteristics as Mars's orbit, its thinning atmosphere, very low magnetic field and gravity, and other factors to explain the mystery of Mars's disappearing water. Yet, we know there IS water and that it does flow from time to time on Mars — from under the Martian surface. Checking Out the Landscape for Water A view from the "Kimberly" formation on Mars taken by NASA's Curiosity rover. The strata in the foreground dip towards the base of Mount Sharp, indicating the ancient depression that existed before the larger bulk of the mountain formed. Credit:NASA/JPL-Caltech/MSSS The evidence for past Mars water is everywhere you look — in the rocks. Take the image shown here, sent back by the Curiosity rover. If you didn't know better, you'd think it was from the deserts of the Southwest U.S. or in Africa or other regions on Earth that were once inundated with ancient ocean waters. These are sedimentary rocks in Gale Crater. They were formed exactly the same way that sedimentary rocks are formed beneath ancient lakes and oceans, rivers, and streams on Earth. Sand, dust, and rocks flow along in water and are eventually deposited. Under lakes and oceans, the material just drifts down and forms sediments that eventually harden to become rocks. In streams and rivers, the force of the water carries rocks and sand along, and eventually, they get deposited as well. The rocks we see here in Gale Crater suggest that this place was once the site of an ancient lake — a place where the sediments could settle down gently and form fine-grained layers of mud. That mud eventually hardened to become rock, just as similar deposits do here on Earth. This occurred over and over again, building up parts of the central mountain in the crater called Mount Sharp. The process took millions of years. These Rocks Mean Water! Exploratory results from Curiosity indicate that the bottom layers of the mountain were built mostly with material deposited by ancient rivers and lakes over a period of no more than 500 million years. As the rover has crossed the crater, scientists have seen evidence of ancient fast-moving streams in the layers of rock. Just as they do here on Earth, streams of water carried coarse pieces of gravel and bits of sand along as they flowed. Eventually that material "dropped out" of the water and formed deposits.In other places, the streams emptied out into larger bodies of water. The silt, sand, and rocks they carried were deposited on the lake beds, and the material formed fine-grained mudstone. The mudstone and other layered rocks provide crucial clues that the standing lakes or other bodies of water were around for quite a long time. They might have widened during times where there was more water or shrank when water wasn't so abundant. This process could have taken hundreds to millions of years.Over time, the rock sediments built up the base of Mt. Sharp. The rest of the mountain could have been built up by continued wind-blown sand and dirt. All that happened a long time in the past, from whatever water was available on Mars. Today, we see only the rocks where lake shores once existed. And, even though there's water known to exist beneath the surface — and occasionally it escapes — the Mars we see today is frozen by time, low temperatures, and geology — into the dry and dusty desert our future explorers will visit.