Scientists: Mars Was Wet, Warm 4 Billion Years Ago

Today's cold, dry climate on Mars evolved about 3.5 billion years ago, ending a period when that planet had seen moist conditions, research indicates.

An international team of scientists developed a timeline for Mars' geological evolution, reporting in Friday's issue of the journal Science that the planet had three distinct eras.

If Mars had been hospitable to life, it would only have been in its early, wet years, according to the researchers led by Jean-Pierre Bibring of France's Institute for Space Astrophysics.

The planet formed about 4.6 billion years ago. During the first era, clay materials, which need abundant water and moderate temperatures, formed, the researchers said.

Then, starting about 4 billion years ago a second era began, marked by volcanic activity spewing sulfur into the environment. That was the start of a drying out of the planet.

Between 3.2 billion years ago and 3.5 billion years ago the third era began. It was marked by minerals dominated by ferric oxides, which have not been formed or altered by water, the researchers said.

That increasingly dry and acidic environment was "not a pleasant place for any form of life, even a microbe," said John Mustard, a Brown University geologist who was a co-author of the paper.

The researchers from France, Italy, Russia, Germany and the United States developed their timetable by studying data from Mars Express. This mission by the European Space Agency carried an instrument capable of determining the mineral composition of the planet's surface. The research was funded by the space and research agencies in all five countries.