In the 20th century, astronomers established that stars, including the Sun, have shone differently throughout their lives: the younger they were, the less they glowed, and vice versa. Scientific works show that 3.770 million years ago, at the time of the birth of life on Earth, the Sun shone 75% less than today, which was not enough to keep water in a liquid state, an essential component for development of the life. However, no signs of glaciations have been found on the planet for this reason.
That ‘regularity’ was first described by Carl Sagan and George Mullen in 1972, and dubbed ‘the weak young Sun paradox’. Since then, many scientists have been trying to solve one of the main mysteries of the correlation between the Earth and the only star in our planetary system. Most often, the paradox has been explained by astrophysical factors or by the composition of the blue planet’s atmosphere.
The last to try to solve the riddle are researchers from the University of Vienna and the Austrian Academy of Sciences. The group of scientists has tried to explain the maintenance of liquid water on Earth by the high level of carbon dioxide and nitrogen gas in the atmosphere of our planet.
To calculate the percentage of CO2 and N2 in the atmosphere, the researchers took as a basis the activity of the sun’s ultraviolet rays, considering that they are actively absorbed by these greenhouse gases. Given the level of solar activity, the Austrian researchers calculated that to counteract UV rays, the minimum percentage of greenhouse gases was around 40%. Such composition of the air on the planet also made it possible to maintain the necessary temperature for there to be liquid water. By comparison, there is only 0.04% CO2 in the air today, supposedly a thousand times less than at the beginning of the planet’s history.