Early Earth Not A Friendly Place For Formation of Life
Four billion years ago, the Earth, at the dawn of life, would have seemed like an alien planet around a violent star. What did this mean for the development of life? Dr. Richard Gray, professor of astronomy at Appalachian State University, is piecing it together with the “Young Solar Analogues” project.
We’re really interested in knowing conditions on the early earth when life first started forming. We believe that the early sun presented some very serious challenges to the development of life on Earth. What we need to do is that we need to study stars like the sun at that stage in their life so that we can understand what our sun was doing back then.
A star’s chemical composition can be determined with spectroscopy. Starlight is broken down into individual colors. Each chemical absorbs a different wavelength of light, leaving identifying black lines, like fingerprints, in the rainbow. Photometry tells us if a star’s brightness remains constant or if it changes. A portrait of the star’s character is constructed with data from these methods, alone or combined with other observations.
We actually surveyed all of the solar type stars within about 130 light years from the earth. It’s called the ‘Nearby Stars Project.’ Out of those stars, we picked about 30 stars that we’re now monitoring that are about the temperature of the sun, so we picked active stars that had ages roughly the range we were interested in.
Through the Young Solar Analogue project, we’ve learned that our early sun presented some enormous challenges for life on Earth.
We know that the early sun had ultraviolet and x-ray output tens, even hundreds of times greater than the present sun. The oxygen we breathe is a result of life tipping our atmosphere into disequilibrium. So, early life lacked some protections. When life first formed, we didn't have oxygen in our atmosphere so we didn’t have an ozone layer to filter out that ultraviolet light, and so a lot of that high energy radiation got right down to the surface of the earth. But another challenge that the early sun presented to life is that the early sun varied quite a bit in its energy output, and that probably meant that the climate on the early earth was highly variable. We have seen some examples of what on our sun would be classed as super-flares, and these would be flares that would just utterly devastate our civilization. You have big ejections of particles that would have interacted with the earth’s magnetic field and more electromagnetic radiation and, you know, lots of violent things happening early on. So we’re trying to understand from our project how often those things happen.
Dr. Gray is using this information to piece together something very important about life on Earth.
All of these things are adding up to the picture that the early earth did not give a very friendly environment for the formation of life, and yet life formed. So the fact that life could form under such hostile conditions is really encouraging for the prospect for life somewhere else in our galaxy. We’re not looking for life. We want to understand what the early sun was like. In extinction we have now discovered thousands of planets around solar-like stars in the zone where the temperature is just right for liquid water to exist on the surface. So our research will give a better understanding of those planets and what they went through when their suns were young. Or perhaps some of those suns are still young, and we can get a better idea of what’s happening currently on those planets.