14 DAY TRIAL // Back when the planet was still very young, rivers and oceans were crisscrossing its surface at a time when they shouldn't have existed, according to theory. The Sun was significantly dimmer then, meaning that Earth should have been covered in ice. Experts now discovered why that didn't happen.
Studies of the Sun revealed that it produced up to 30 percent less light some 4 billion years ago than it does today. At the time, the star was still young, and had not yet reached its main sequence stage.
Why the planet was not covered in ice at the time is a matter still open for debate, but several proposals have crystallized in the meantime, dividing the international scientific community in the process.
While some researchers proposed that a runaway greenhouse gas effect kept the planet warm, others suggested that a much thicker atmosphere – similar to the one now surrounding Saturn's largest moon, Titan – was responsible for the effect. A combination of the two was also proposed as an explanation.
Recently, an analysis of fossilized rain droplets, dated to 2.7 billion years ago, demonstrated that an increased concentration of greenhouse gases – including carbon dioxide (CO2) and methane (CH4) – was most likely responsible for keeping the planet warm enough to support liquid water.
Geologic evidence suggests that rivers and ocean sediments were deposited on the planet between 4 and 2 billion years ago, say investigators from the University of Washington. Their work is published in the March 28 issue of the top scientific journal Nature.
“Because the Sun was so much fainter back then, if the atmosphere was the same as it is today the Earth should have been frozen,” Sanjoy Som explains. The expert was the lead author of the work, which he conducted while he was a PhD student in Earth and space sciences at UW.
Som is now a postdoctoral investigator at the NASA Ames Research Center (ARC), in Mountain View, California. Scientists at UW collaborated with colleagues at the Edinburgh Center for Low Carbon Innovation, in Scotland, UK, for this investigation.
“Setting limits on atmospheric pressure is the first step towards understanding what the atmospheric composition was then. Knowing this will double the known data points that we have for comparison to exoplanets that might support life,” the investigator goes on to say.
“Today’s Earth and the ancient Earth are like two different planets,” he concludes, quoted by Astrobiology Magazine.