Scientists at the NASA/Goddard Space Flight Center think they've figured out how the ‘spin’ of the Sun influenced life here on Earth - by using the Moon as critical evidence.
When the Sun was just a baby four billion years ago, it went through violent outbursts of intense radiation, which helped seed life on early Earth by igniting chemical reactions that kept Earth warm and wet. The scientists wondered why is there significantly less sodium and potassium in lunar regolith, or Moon soil, than in Earth soil? Then they realized that the history of the Sun is buried in the Moon's crust.
They simulated the effect solar activity has on the amount of sodium and potassium that is either delivered to the Moon's surface or knocked off by a stream of charged particles from the Sun, known as the solar wind, or by powerful eruptions known as coronal mass ejections (CMEs).
They incorporated the mathematical relationship between a star's rotation rate and its flare activity. According to their estimates, within its first billion years, the Sun took at least 9 to 10 days to complete one rotation. As a slow-rotating star it was able to blast the right amount of charged particles into the Moon's surface to knock enough sodium and potassium into space over time to leave the amounts we see in Moon rocks today. The aging Sun gradually slowed its pace and continues to do so. Today, it revolves once every 27 days, three times slower than it did in its infancy.
The Sun is why we're here. It rotated at an ideal pace for Earth, which thrived under the early star. Venus and Mars weren't so lucky. Both once had oceans and were habitable by physical life forms similar to ours, but eventually lost their seas and air, although water still exists on Mars, frozen in the polar caps and in the soil.
The reason the Moon is a useful calibrator and window into the past is that it has no annoying atmosphere and no plate tectonics resurfacing the crust. If astronauts can get samples of lunar soil from the Moon's southernmost region in future, it could offer more physical evidence of the baby Sun's rotation rate.
Source: Science Daily.com (June 17, 2019)