SOME astrophysicists try to understand the composition of planets that go round other stars — so-called “exoplanets.” They do so by looking at how light from the star is absorbed as the planet orbits around it, which allows them to find out the compounds that make up the planet’s atmosphere.

The technique allows scientists to understand something about these distant planets, though they are separated by many light years.

Some scientists believe that by identifying specific molecules in the atmospheres of these planets, we will be able to observe the signature of life. These signatures would be “biomarkers” — molecules that can’t be produced by simple chemistry, but can only be made by living organisms.

The difficulty in assessing these molecules and the remoteness of the planets make others sceptical that any biomarker would, by itself, ever be enough to categorically say that life exists.

What if life on other planets was very different to ours?

One significant issue in the analysis of these distant atmospheres is whether their atmospheres are in a steady state, more or less unchanging, or not.

If you imagine a mixture of chemicals in a jar — for example, salt and pepper — it would be reasonable to assume that nothing is really changing. No reactions are gradually transforming the salt and pepper into something else.

This wouldn’t be true if the jar contained a burning match, or a mouse. In the universe things are often in a process of change, whether alive or not.

The composition of our own planet’s atmosphere is also a pressing concern. The extreme increase in the amount of CO2 has caused global heating, destabilising the climate.

However, beyond the future of life on Earth, there are scientists that try to decipher the history of our atmosphere. They do so in order to understand more about life’s origins and subsequent development.

This early atmospheric analysis is largely done by looking at ancient rock. Some rock has been transformed by the movement of the Earth’s crust since it first formed.

However, there are also rocks that have been untouched since their original formation. Rocks formed by sediments dropping to the bottom of the ocean and settling there are one example.

These sediments are interesting because of what they reveal about the elements dissolved in the ocean at the time they fell. Those elements in turn tell us about life, because life as we know it has certain processes that produce known molecules, which can help scientists build a picture of what living organisms might have been like before they were big and complex enough to be fossilised.

This data means that unlike life on other planets, about which we could only speculate, scientists can have clearer theories (though they remain only theories) about what early lifeforms looked like.

Oxygen is one of the most significant elements for the analysis of Earth’s ancient atmosphere. The rocks that have been used most commonly to understand its most important oxygen transition contain stripes called banded iron formations.

These are widespread depositions of iron, which look like red lines of variable thickness, interspersed with white, grey or brown rock containing very little iron.

The stripes of rock formed long ago and are not being formed today. They are found all over the world and can be hundreds of metres below the crust.

Although rock like this is no longer being laid down, these deposits store 60 per cent of the world’s iron and are the most common source of mined iron ore.

The most accepted theories of how this particular rock came to be tell us that the stripes show the sputtering into being of an atmosphere rich in oxygen.

Prior to this time, the Earth’s atmosphere is thought to have been anoxic, containing no oxygen. The lack of oxygen allowed iron to dissolve in the water freely.

At the point of the earliest occurrence of the banded rock, it is thought that oxygen was produced by the earliest respiring bacteria. This oxygen dissolved in the iron-rich water, and immediately reacted with the iron to make compounds that were no longer soluble, but instead sunk to the bottom of the sea.

In some places, it is thought this deposition could have occurred at rates of metres of rock per year. The rock that resulted from this process is red, like rust, thanks to the iron.

Oxygen in the atmosphere of a distant star might well be a biomarker of life. Oxygen is extremely reactive. It has a tendency to combine with other atoms, to combust, and to change the materials with which it comes into contact.

This reactivity is also what means that it doesn’t just pop out of water, which is itself made of hydrogen and oxygen.

To early life, it is thought that this reactivity would have made oxygen highly toxic. The bacteria that first produced oxygen could therefore have been killed off by the product that they made. It would require additional adaptations in early life-forms before they could tolerate living in environments with lots of oxygen.

Until this happened, it is thought that populations of bacteria may have cycled in waves, repeatedly killed by oxygen, reducing the production of that oxygen until levels were low enough that the bacteria could re-emerge in large numbers and begin the cycle again.

These theories provide a compelling image of how the earliest life may have radically changed the composition of the world that it lived in, itself adapting to live in the world that it had created.

This week scientists reported a surprising discovery. They found that oxygen can be created deep down on the ocean floor: not by bacteria, but by metallic nodules. The metal nodules act as little batteries and split deep ocean water into hydrogen and oxygen through electrolysis.

This is an important discovery, because it shows that biological processes are not the only way that oxygen can enter the atmosphere. That makes the interpretation of atmospheric composition of exoplanets less straightforward.

It seems unlikely that it will fundamentally disrupt the dominant theories of early oxygenation, but it is a reminder that something non-biological could have played a role, on Earth, and on other planets too.

It is to the credit of the scientists and those that worked with them to get the scientific discovery into the news. The research was funded by a mining company, who hope to retrieve the metals responsible for producing the oxygen — perhaps for use in artificial batteries, or even electrolysis.

The nodules of metal are in themselves a remarkable phenomenon. They fundamentally alter the ecology of the deep sea, and perhaps the ocean and its rock on a grander scale too.

Unlike the fast deposited iron sediments, the nodules are believed to form at a rate of centimetres over millions of years. They are just one part of what stands to be lost if deep sea mining goes ahead, as it currently threatens to.

Although we know that the atmosphere of Earth will always change and evolve, the speed of change now is happening much faster than geological timescales.

There is no justification for using up resources at the pace demanded by the short-term logic of mining, of fossil fuels or metals.

The original oxygen-producing bacteria were lucky to persist through the toxic products they released into the atmosphere. The disequilibrium that they produced oscillated until they could live successfully. Not all species that initiate out-of-equilibrium processes are so lucky.