We were pretty sure even before the first lander grounded on Mars, the red colour of the planet is due to a lot of iron oxide in the rocks and sands making up its surface.

Some recent research suggests the form of iron oxide making the “Red Planet” red required both oxygen and water. We know there was a lot of water on the Martian surface billions of years ago, and the prospect of oxygen suggests life.

To get an idea of what might have happened on Mars we should look at the early history of our planet.

Our planet formed along with the other planets of the Solar System about 4.5 billion years ago. As soon as the Earth had cooled enough for water to accumulate on its surface, the processes leading to life got under way. However, from our point of view, the conditions were hostile. The atmosphere consisted of gases like hydrogen, carbon dioxide, methane, ammonia and a collection of hydrocarbons. There was no oxygen.

The first living things were........

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