A new study shows that the earliest conditions on our planet were probably even more hostile than originally thought, and it's because scientists have been doing a lot of work to figure out what ancient Earth would have looked like.
Researchers think that the levels of UV radiation from the Sun that reach the surface of Earth could be up to 10 times higher than previously thought.
The last 2.4 billion years of history are the focus of the research. The new findings will teach us more about Earth's history and could help us understand the atmospheres on other planets.
"If life is exposed to too much UV radiation, it can have disastrous effects," says Gregory Cooke, an astronomer from the University of Leeds in the UK. It can cause skin cancer in humans. Some organisms can repair damage caused by UV radiation.
It could have acted as a selection pressure, with organisms better able to cope with greater amounts of UV radiation receiving an advantage, if elevated amounts of UV radiation had not prevented life's emergence or evolution.
The researchers think that the ozone layer could have been weakened by higher levels of UV radiation. Oxygen levels play a major role in the formation of ozone in our atmosphere.
It was thought that atmospheric oxygen levels of 1 percent would produce enough ozone to keep harmful UV radiation away. The team suggests that the key oxygen level may be less than 10%.
There are questions about how much UV light has gotten through to Earth over the past 2 billion years. The Royal Society Open Science is headed by Greg Cooke.
It is possible that for a long period of time, when we thought there was enough ozone around to block UV rays, that was not the case. The researchers say that this has a knock-on effect on life on Earth.
"If our modeling is indicative of atmospheric scenarios during Earth's oxygenated history, then for over a billion years the Earth could have been bathed in UV radiation that was much more intense than previously believed." This may have had interesting consequences for life's evolution.
The researchers say that the increased levels of UV radiation may have been responsible for a mass extinction.
The authors of the new study are calling for the ozone levels in the atmosphere to be reexamined because of the potential damage that this type of radiation can cause. There are multiple factors that need to be taken into account.
Oxygen levels in the atmosphere got up to modern-day standards around 400 million years ago, and more complex life forms began to evolve, leading to the wide diversity in evidence across the planet today.
It is not known when animals emerged or what conditions they encountered in the ocean or on land.
Animals and plants could have faced harsher conditions if oxygen concentrations were higher. We hope that the full evolutionary impact of our results can be explored in the future.
The research has been published.
