Earth's history is recorded in its rocks. Layers of sediment, compressed and cemented to form rock, tell tales of the comings and goings of seas, mountain ranges, rivers, volcanoes, and deserts. Earth's sedimentary rocks record changes in climate and biodiversity over time. Most of what is known about Earth's past comes from the study of layered rock and the materials---grains, structures, and fossils---found within them.

Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images have very high resolution, allowing detection of objects the size of school buses and airplanes. Such images are comparable to the aerial photographs used by geologists on Earth to plan their fieldwork in areas of layered sedimentary and volcanic rock. Hundreds of MOC images have revealed outcrops of layered rock exposed by erosion and faulting in craters and chasms on the red planet.

Martian sedimentary rocks are just now beginning to reveal clues about the planet's complex early history. "Early Mars" refers to a time thought to have been more than 3.5 billion years ago, a period when the planet was young and impact craters---created by meteors, asteroids, and comets hitting the surface---were forming more frequently than they do today.

The history suggested by the martian sedimentary rocks may have included warm, wet climates with thousands of crater lakes (i.e., with liquid water) that persisted for millions of years. Alternatively, the rocks might be recording climate changes and thick deposits of airborne dust formed on a much colder, drier world than many have suspected. In either case, the images indicate that early Mars was very different from the planet today, and its history---recorded in rocks---beckons further exploration.

The evidence for sedimentary rocks and their record of early martian history is described in a paper by MGS MOC scientists published in the December 8, 2000, issue of Science. The pictures accessed via the links below illustrate some of the attributes of martian sedimentary rock. Interested individuals may also find hundreds of additional examples in places such as the Valles Marineris, western Arabia Terra, northeastern Hellas, and Terra Meridiani, by searching through the 57,500+ images of the MGS MOC Gallery.

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MOC2-259 W Candor Chasma

MOC2-260 Gale Crater Mound

MOC2-261 8°N, 7°W Crater

MOC2-262 Holden Crater

MOC2-263 Marineris Walls

MOC2-264 Pollack Crater

MOC2-265 "TV" Illustrations

MSSS Image Use Policy

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Malin Space Science Systems, Inc.

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