Scientists have discovered microbes and other microscopic life living in extreme conditions on Earth—for example, on the ocean floor and deep in the Earth’s crust. This illustration shows micro-organisms (one at centre) deep underground on Mars. These micro-organisms are based on extremophiles found on Earth: specifically, a range of eukaryotic organisms found in biofilms deep in mines of South Africa. Read more about the making of this science illustration in our Mars case study.