A forest of the Permian period (artist’s impression), which saw atmospheric oxygen levels peak at more than 35%.Credit: Richard Jones / Photo Library Science
The force of the magnetic field of the earth seems to increase and fall hand in hand with the abundance of oxygen in its atmosphere, a study of geological files covering the last half-milliards of years revealed.
Explaining the link could help reveal the fundamental trends in the evolution of life on earth – and could show astronomers the most promising places to seek signs of complex life on other planets. But so far is not very clear if the magnetism of the earth plays a direct role in maintaining the life of oxygen levels – and the maintenance of animal life – or if the two are influenced by a third unidentified mechanism.
Source: Ref. 1Source: Ref. 1
“We don’t really have a good explanation for this,” explains Benjamin Mills, biogeochemist at the University of Leeds, in the United Kingdom, and co-author of the study, published in Scientific advances June 131. But the study suggests “certain potential causes that are exciting and potentially testable,” said Aubrey Zerkle, a biogeochemist at the University of St Andrews, in the United Kingdom.
Knowing how the deep interior of the earth could influence the evolution of the atmosphere is “essential to understand what makes our planet habitable”, explains Richard Bono, geophysicist of Florida State University in Tallahassee who helped compile long -term recordings of geomagnetism.
Geological indices
Oxygen is the main component of the crust and the mantle of the earth. But molecular oxygen has only started to accumulate slowly in the atmosphere that organisms that produce oxygen by photosynthesis have started to evolve, around 2.5 billion years ago. And it is only in the current AEON, covering the last 540 million years, he reached concentrations which are breathable by most animals.
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There is no direct way to measure the composition of the atmosphere in the deep past, but geochimists can use indirect clues2 To rebuild the oxygen levels from the Cambrian period, which started around 540 million years ago. For example, the oxygen concentration “has a solid relationship with the ease with which it is to start and maintain forest fires”, explains Mills, and the frequency of large forest fires can be developed by examining the deposits of old wood of wood, among other factors.
Geophysicists can also rebuild how the strength and direction of the geomagnetic field varied to the other longer stretching in the history of the earth, by studying the rocks produced by ancient volcanic eruptions3. Indeed
To put these two long discs side by side and compare them, Mills teamed up with geophysicists Weijia Kuang and delighted Kopparapu, both at NASA Goddard Space Flight Center, Greenbelt, Maryland, and with exobiologist Joshua Krissansen-Totton at the University of Washington in Seattle. The authors have found a strong correlation – oxygen levels and geomagnetic intensity increased over millions of years, and some of the main peaks or decreases in the two measurements occur in the same geological eras (see “long -term trends”).
Possible explanations
The document discusses certain possible reasons for the correlation. The magnetic field of the earth is known to have a protective effect on the upper atmosphere because it pours the solar wind, a flow of particles charged with the sun which otherwise cause oxygen and other gases escaping slowly in space. But the team calculated that the loss of oxygen caused by a drastic weakening of the field would always be low compared to the quantities generated by photosynthesis – or to those consumed by other organisms and by geological cycles in which elements are exchanged between the atmosphere, the crust and the coat.