14 DAY TRIAL // Even from its earliest stages of its existence, Earth has been covered in water. Geologists know this from ample sources, and they believe that there is no reason to doubt the geological findings. However, for the past 50 years or so, scientists have been puzzled by a strange question. How could there be liquid oceans on the planet for the first half of its 4.5-billion-year-long existence, given that the Sun was at the time only 70 percent as luminous as it is today? This question was first posed by Carl Sagan and George Mullen in 1972, and it's only now that experts believe they may have found the answer.
This early Earth climate paradox has been bugging investigators for a long time. Technically speaking, the lower luminosity of the Sun would have translated into less heat reaching the surface of the planet. Without this extra heat, the liquid oceans should have frozen over. However, a massive body of data stands evidence to the contrary. Previous studies have discovered that not only were there liquid oceans on Earth, but also primitive forms of life. If the Sun indeed shone less, then this shouldn't have been the case, experts say, quoted by LiveScience.
A number of explanations were proposed by the international scientific community over the years, to try and account for this paradox, but they have been struck down one by one. The most accurate explanation that researchers could come up thus far is that a global warming effect kept the planet at higher temperatures than the Sun alone would have allowed. In order to validate this hypothesis, which was first proposed in the 1980s or so, geologists looked at samples collected from 3.8-billion-year-old mountain rock. These were collected from a swath of sedimentary rock called Isua, which can be found in Greenland and which is widely believed to be the oldest deposit on the planet.
Many believe that the atmosphere of the planet may have contained about 30 percent carbon, as opposed to the 0.038 percent CO2 it does at this point. But investigations of the sediments told a different story. “The analyses of the CO2 content in the atmosphere, which can be deduced from the age-old rock, show that the atmosphere at the time contained a maximum of one part per thousand of this greenhouse gas. This was three to four times more than the atmosphere's CO2 content today. However, not anywhere in the range of the 30 percent share in early Earth history which has hitherto been the theoretical calculation,” explains University of Copenhagen in Denmark expert Minik Rosing.
He and his group explain that a much more possible explanation may have been that the early Earth was covered in a blanket of clouds that may have allowed more sunlight to pass through, while at the same time trapping heat underneath. However, not everyone is convinced that this is what actually happened. The team is currently waiting to see what arguments are brought against their proposal.