One of science's great mysteries unravelled

Hindu Bureau


In 1972, the late, world famous astronomer Carl Sagan and his colleague George Mullen formulated ‘The faint early sun paradox'. The paradox consisted in that the earth's climate has been fairly constant during almost four of the four and a half billion years that the planet has been in existence, and this despite the fact that radiation from the sun has increased by 25-30 per cent.

The paradoxical question that arose for scientists in this connection was why the earth's surface at its fragile beginning was not covered by ice, seeing that the sun's rays were much fainter than they are today.

Science found one probable answer in 1993, which was proffered by the American atmospheric scientist, Jim Kasting. His calculations showed that 30 per cent of the earth's atmosphere four billion years ago consisted of CO{-2}.

This in turn entailed that the large amount of greenhouse gases layered themselves as a protective greenhouse around the planet, thereby preventing the oceans from freezing over.

Professor Minik Rosing from the Natural History Museum of Denmark explains, “What prevented an ice age back then was not high CO{-2} 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,” Prof Rosing said. 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.

The team analysed samples of 3.8-billion-year-old mountain rock from the world's oldest bedrock, Isua, in western Greenland, to solve the ‘paradox.'

Important issue
But more importantly, the analyses also provided a finding for a highly important issue in today's climate research — and climate debate, not least: whether the atmosphere's CO{-2} concentration throughout earth's history has fluctuated strongly or been fairly stable over the course of billions of years.

"The analyses of the CO{-2}-content in the atmosphere, which can be deduced from the age-old Isua 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 CO{-2}-content today.

However, not anywhere in the range of the of the 30 per cent share in early earth history, which has hitherto been the theoretical calculation.

Hence we may conclude that the atmosphere's CO{-2}-content has not changed substantially through the billions of years of earth's geological history.