Powerful solar explosions on the adolescent Sun may have provided the crucial energy needed to warm Earth and create complex molecules necessary for life, despite the star's faintness four billion years ago, according to a new NASA study.
Understanding what conditions were necessary for life on our planet helps us both trace the origins of life on Earth and guide the search for life on other planets. Until now, mapping evolution has been hindered by the fact that the young Sun was not luminous enough to warm Earth.
Some four billion years ago, the Sun shone with only about three-quarters the brightness we see today, but its surface roiled with giant eruptions spewing enormous amounts of solar material and radiation out into space. These powerful solar explosions may have provided the crucial energy needed to warm Earth.
They also may have furnished the energy needed to turn simple molecules into the complex molecules such as RNA and DNA that were necessary for life. "Back then, Earth received only about 70 per cent of the energy from the Sun than it does today," said Vladimir Airapetian, from NASA's Goddard Space Flight Centre in US.
"That means Earth should have been an icy ball. Instead, geological evidence says it was a warm globe with liquid water," said Airapetian. "Our new research shows that solar storms could have been central to warming Earth," he said.
Scientists are able to piece together the history of the Sun by searching for similar stars in our galaxy. By placing these Sun-like stars in order according to their age, the stars appear as a functional timeline of how our own Sun evolved.
It is from this kind of data that scientists know the Sun was fainter 4 billion years ago. Such studies also show that young stars frequently produce powerful flares - giant bursts of light and radiation - similar to the flares we see on our own Sun today.
Such flares are often accompanied by huge clouds of solar material, called coronal mass ejections (CME), which erupt out into space.
Earth today has a strong magnetic field that helps keep the bulk of the energy from such space weather from reaching the planet.
Our young Earth, however, had a weaker magnetic field, with a much wider footprint near the poles. "Our calculations show that you would have regularly seen auroras all the way down in South Carolina," said Airapetian.
"And as the particles from the space weather travelled down the magnetic field lines, they would have slammed into abundant nitrogen molecules in the atmosphere," he said. "Changing the atmosphere's chemistry turns out to have made all the difference for life on Earth," he added.
The research was published in the journal Nature Geoscience.