One of the most tantalising questions in science is whether there is or ever has been life on Mars, at least in microbial form. But despite plenty of effort – including orbiting missions and even rovers that have analysed its red rocks and soil – we have so far not managed to detect any conclusively.

Now we have new techniques that could actually detect traces of past microbial life in meteorites from Mars here on Earth. We know the method itself works: we have used it to detect traces of ancient life in basalt rocks on Earth for the first time. And the best thing about it is that these rocks are very similar to those found on Mars.

Surfaces are key to this. It may seem like we live in three dimensions but I’d like to argue that we mostly live in two. Almost all the objects we see (except glass, some plastics and the occasional crystal) are opaque, so we only see and interact with the surface. Life is, in many ways, a surface effect.

We think the tunnels in these 220 million-year-old rocks have been left by the finger-like branching filaments of fungi

Things grow on the surface of my coffee cup in my office over the weekend. Occasionally, I’ll give it a rub (on the surface) to clean it up a bit, but I need a cloth with the right type of surface to do it. In more serious biological and medical cases surfaces are critical. Antibiotic and antifungal medicines largely work by disrupting the surfaces of bacteria and fungi. The NHS spends an enormous amount each year replacing catheters when things grow on their surfaces. The list goes on. Surfaces matter.

Some of the earliest forms of life on our planet were forced to make their own surfaces to live on. It was by looking at surfaces from samples of basalt rock from hundreds of metres under the floor of the Pacific Ocean that we managed to discover organic compounds deposited around microscopic “tunnels”.

We think the tunnels in these 220 million-year-old rocks have been left by the finger-like branching filaments of fungi, possibly to find nutrients or seek protection from predators. Similar structures have been seen in 3.3 billion year-old rocks, which could make them evidence of some of the earliest life on Earth.

The research suggests that these microbe-made surfaces may be a good place to begin looking for life elsewhere. While we are not sure exactly how long the traces of biomolecules survive, we know that some are extremely robust.

These are the only bits of Mars we can take a look at right now

It is increasingly clear from looking at fossils, for example, that tenacious molecules like melanin can remain for hundreds of millions of years and give a clue to the colouring of dinosaurs.

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