Nearly forty years ago, Carl Sagan and George Mullen puzzled over the ‘faint early Sun paradox’, wondering why the Earth was not frozen solid at a time when radiation from the sun was 25 to 30 percent less than today.
One hypothesis has been that the carbon dioxide content of the atmosphere was radically greater then than now, creating a powerful greenhouse effect. But a pair of Danish scientists and their American colleagues have now made the case for a much different reason, even while debunking the evidence for super concentrations of CO2 in the atmosphere.
As explained in Danish Researcher Unravels One of Science’s Great Mysteries from the University of Copenhagen,
“Professor Minik Rosing, from the Natural History Museum of Denmark, and Christian Bierrum from the Department of Geography and Geology at UC, together with American colleagues from Stanford University in California have discovered the reason for ‘the missing ice age’ back then, thereby solving the sun paradox, which has haunted scientific circles for more than forty years.
“Professor Minik Rosing explains, ‘What prevented an ice age back then was not high CO2 concentration in the atmosphere, but the fact that the cloud layer was much thinner than it is today. In addition to this, the earth’s surface was covered by water. This meant that the sun’s rays could warm the oceans unobstructed, which in turn could layer the heat, thereby preventing the earth’s watery surface from freezing into ice. The reason for the lack of clouds back in earth’s childhood can be explained by the process by which clouds form. This process requires chemical substances that are produced by algae and plants, which did not exist at the time. These chemical processes would have been able to form a dense layer of clouds, which in turn would have reflected the sun’s rays, throwing them back into the cosmos and thereby preventing the warming of earth’s oceans. Scientists have formerly used the relationship between the radiation from the sun and earth’s surface temperature to calculate that earth ought to have been in a deep freeze during three billion of its four and a half billion years of existence. Sagan and Mullen brought attention to the paradox between these theoretical calculations and geological reality by the fact that the oceans had not frozen. This paradox of having a faint sun and ice-free oceans has now been solved.”
Using 3.8 billion year old bedrock from Greenland, the researchers have also determined that, while elevated above present-day percentages, the atmospheric content of carbon dioxide never approached the 30 percent required by the greenhouse hypothesis. This latter observation may well have implications for all of us as we begin to approach historically unprecedented levels of atmospheric CO2.