"Why Earth beats Mars when it comes to hospitality"

Life on Earth was made possible by the planet’s ability to stockpile oxygen beneath its surface, researchers say.

Oxygen is transported, as part of iron oxide, by geological movements deep beneath the Earth’s crust where pressure and heat transform it into an ingredient of the mineral majorite. When majorite is moved close to the surface it becomes unstable and begins to release oxygen, which can then bind with hydrogen to form water.

“Without this mechanism our ‘Blue Planet’ might well be as dry and inhospitable as Mars,” a study in the journal Nature concluded.

Christian Ballhaus, of the Mineralogical Institute at Bonn University, said that the movement of the mineral to the top of the mantle, between the Earth’s core and crust, was crucial. “That’s where the stored oxygen is released,” he said. “Near the surface it is made available for all the oxidation reactions that are essential for life on Earth.

“If our planet did not have the ability to store oxygen in the deep reaches of its mantle there would probably be no life on its surface.”

The multinational research team described the process as an “oxygen elevator”, without which “the Earth would probably be a barren planet, hostile to life”.

The size of the Earth is an essential factor, they said. Much smaller, and the heat and pressure generated are inadequate for the necessary geological processes. The Earth, with a diameter of 7,926 miles (12,756km), still has a changing mantle whereas Mars, with a diameter of 4,350 miles, cooled down long ago and no longer has any movement. Professor Ballhaus said of Mars: “Its crust has therefore lost the ability to transport oxygen and maintain a lasting, water-rich atmosphere.”

Arno Rohrbach, of the University of Bonn, added: “According to our findings, planets below a certain size hardly have any chance of forming a stable atmosphere with a high water content. The pressure in their mantle is just not high enough to store sufficient oxygen in the rock and release it again at the surface.”