What really lies across the surface of Mars? Rovers have scurried about the red planet for years, drilling, scooping and analyzing for signs of life, past or present. But to really understand the Martian landscape, scientists need to look at the entire surface. What they have needed is a global geologic map.

The red planet is long overdue for a new one. The last major effort in Martian cartography was published in 1987, scraped together from the early Viking probes’ scant images and datasets. Since then, four additional orbiters with superior imaging capabilities have journeyed into Martian orbit, collected data and transmitted their findings back to Earth.

Now, scientists at the United States Geological Survey have used that data to create an updated map of the entire Martian surface. The new map shows that ancient rock — dating back billions of years ago, when Mars’s environmental conditions might have closely resembled Earth’s— exists in many more locations than previously thought. Because the map highlights the location of the oldest rocks on Mars, it could help future missions chart a course for these areas.

“We are disproportionately interested in the early part of Martian history,” said David Beaty, the chief scientist for the Mars Exploration Directorate at the Jet Propulsion Laboratory in Pasadena, Calif., who was not involved in the research. “It was during that period that more water would have been around, which is one of the key aspects of the origin of life.”