New research reveals more hostile conditions on Earth as life evolves


Graph showing how UV radiation on Earth has changed over the past 2.4 billion years. Credit: Gregory Cooke / Royal Society Open Science

For long parts of the past 2.4 billion years, Earth may have been more inhospitable to life than scientists previously thought, according to new computer simulations.

Using an advanced climate model, researchers now believe the level of ultraviolet (UV) radiation reaching the Earth’s surface could have been underestimated, with UV levels up to ten times higher. students.

UV radiation is emitted by the sun and can damage and destroy biologically important molecules such as proteins.

The past 2.4 billion years represent an important chapter in the development of the biosphere. Oxygen levels have risen from almost zero to significant amounts in the atmosphere, concentrations fluctuating but eventually reaching modern concentrations about 400 million years ago.

During this time, more complex multicellular organisms and animals began to colonize the earth.

Timeline showing the change in Earth's oxygen concentrations

A rough overview of the oxygen (O2) concentrations in the Earth’s atmosphere over time is shown in this figure. The brown blocks show the estimated range of O2 based on its current air level (which is 21% by volume). The gray-blue lines indicated various events important to the evolution of life, including the emergence of eukaryotes and animals. Black arrows refer to important events where the atmospheric oxygen concentration has changed. The Archean, Proterozoic and Phanerozoic are geological eons. GOE = Large oxidation event; NOE = neoproterozoic oxidation event; CE = Cambrian Explosion; LE = Lomagundi excursion. Credit: Gregory Cooke / Royal Society Open Science

Gregory Cooke, a doctoral researcher at the University of Leeds who led the study, said the findings raise new questions about the evolutionary impact of UV radiation, as many life forms are known to be adversely affected by intense doses of UV radiation.

He said: “We know UV rays can have disastrous effects if life is too exposed. For example, it can cause skin cancer in humans. Some organisms have effective defense mechanisms, and many can repair some of the damage caused by UV rays.

“While high amounts of UV radiation would not prevent the emergence or evolution of life, it could have acted as selection pressure as organisms are better able to cope with larger amounts of radiation. UV receiving an advantage. “

The research “A revised lower estimate of ozone columns during the oxygenated history of the Earth” was published on January 5, 2022 in the scientific journal Royal Society Open Science.

The amount of UV radiation reaching Earth is limited by ozone in the atmosphere, described by researchers as “… one of the most important molecules for life” due to its role in absorbing UV radiation. when it enters the Earth’s atmosphere.

Ozone is formed as a result of sunlight and chemical reactions – and its concentration depends on the level of oxygen in the atmosphere.

For the past 40 years, scientists have believed that the ozone layer is able to protect life from harmful UV rays when the level of oxygen in the atmosphere reaches about one percent of the current atmospheric level.

The new modeling calls this assumption into question. This suggests that the level of oxygen needed may have been much higher, perhaps 5-10% of current atmospheric levels.

As a result, there have been times when UV radiation levels on the Earth’s surface were much higher, and this could have been the case for most of Earth’s history.

Mr Cooke said: “If our modeling indicates atmospheric scenarios over the oxygenated history of the Earth, then for over a billion years the Earth could have been bathed in much more intense UV radiation. than previously believed.

“It could have had fascinating consequences on the evolution of life. It is not known precisely when the animals emerged, or what conditions they encountered in the oceans or on land. However, depending on the oxygen concentrations, animals and plants could have faced much more difficult conditions than the world today. We hope that the full evolutionary impact of our results can be explored in the future. “

The results will also lead to new predictions for exoplanet atmospheres. Exoplanets are planets orbiting other stars. The presence of certain gases, including oxygen and ozone, may indicate the possibility of extraterrestrial life, and the results of this study will help scientific understanding of surface conditions on other worlds.

Reference: “A Revised Lower Estimate of Ozone Columns During Earth’s Oxygen History” by GJ Cooke, DR Marsh, C. Walsh, B. Black and J.-F. Lamarque, January 5, 2022 , Royal Society Open Science.
DOI: 10.1098 / rsos.211165

The study was funded by the UK Science and Technology Facilities Council and involved collaboration with scientists from the National Center for Atmospheric Research, Rutgers University and the City University of New York, all located in the United States.


Comments are closed.