Researchers compared atmosphere and radiation models of exoplanets with Earth of nearly 4 billion years ago to today. 4 billion years ago the Earth had a lot more radiation but life still existed and started at that time.
Nearby exoplanets are receiving higher UV radiation than that emitted by our own sun today but the radiation is significantly lower than what Earth received 3.9 billion years ago.
To judge the potential habitability of worlds with varying rates of radiation influx, the researchers assessed the mortality rates at different UV wavelengths of the extremophile Deinococcus radiodurans, one of the most radiation-resistant organisms known.
Not all wavelengths of UV radiation are equally damaging to biological molecules. A dosage of UV radiation at 360 nanometers would need to be three orders of magnitude higher than a dosage of radiation at 260 nanometers to produce similar mortality rates in a population of this organism.
The researchers modeled the surface UV environments of the four exoplanets closest to Earth that are potentially habitable: Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b.
SOURCE- Cornell University, Monthly Notices of the Royal Astronomical Society