Four billion years ago, Mars was not the dry red desert it is today. It had flowing water and lakes. Maybe even life. And researchers have uncovered new evidence on where traces of that life could be hiding.
According to work published in the Journal of Geophysical Research: Planets, iron-rich sedimentary rocks from ancient lakeside regions are probably our best bet for finding the fossilized remains of ancient life forms. Even if they were very primitive when they died.
Lakebed rocks have a lot going for them. Life as we know it needs water, so if there was life on Mars, it would likely have occurred near water. Microbes would have found their way to lakebed sediments where mud and clay rich in iron and silica would have eventually helped to fossilize them. When the water dried out and the sediments became rocks, any traces of ancient life would have been preserved within them.
The research will play an important part in selecting the objectives for future rover missions such as NASA’s Mars 2020 and the ExoMars rover from the European Space Agency. Both missions are expected to collect samples that – hopefully – will then be sent back to Earth for analysis.
"There are many interesting rock and mineral outcrops on Mars where we would like to search for fossils, but since we can't send rovers to all of them we have tried to prioritise the most promising deposits based on the best available information," lead author Dr Sean McMahon, from the University of Edinburgh, said in a statement.
The available information was not easy to come by. The international team of researchers simulated Mars conditions to work out which kind of soil would be the most likely to conserve biological signatures for billions of years. And iron-rich sedimentary rocks appear to be the best bet. The experiments had to be done in the lab because naturally occurring rocks of the same age on Earth are not well preserved. Plate tectonics, which Mars doesn’t have, messes with the rocks.
Researchers have used the data that other missions have collected on Mars to work out what the Red Planet was like in the past. Between 3 and 4 billion years ago, its abundant water reservoir and dense atmosphere might have allowed life to emerge. We’ll just have to wait to see if there really was life on Mars long ago.