Saturday, March 24, 2012

Mother Earth is Losing Water

The other day I found an article on the internet based on a scientific publication pointing out that Mother Earth has not just one but two water leaks. It turns out that over the last 3.8 trillion years we have drained water at such a rate that a mass corresponding to the volume of the Atlantic Ocean has been lost. The same amount added today would increase the sea level by 800 m. Figure out yourself what this would mean for the place you live.

Emily Pope of the University of Copenhagen and her coworkers base their findings on an analysis of early formed deep lying serpentine rock layers in Greenland. Those 3.8 Ga old silicates  (i.e. only slightly younger then the age of the earth of 4.5 Ga) show a remarkable difference in isotope composition compared with more recently formed minerals of the same kind.

As the article points out one of the earth's water leaks is due to the diffusion of hydrogen into space. The chemical processes involved start out with methane (CH4) formed by a plausible biogenic source for methanogenesis with a concentration of this gas 60 times higher in the Archaean atmosphere than in today's. Methane undergoes photolysis in the upper atmosphere in a reaction CH4 + 2O2 → CO2 + O2 + 4H where some of the hydrogen formed in the process will diffuse into space. This evaporated hydrogen is lost for the formation of water. There is also deuterium the heavier hydrogen isotope better known in its combination with oxygen as heavy water. Deuterium, however, reacts more poorly with oxygen than hydrogen and in addition diffuses at a much lower rate. The net effect is that compared with the water in the Archaean oceans today's seawater is enriched in deuterium and hence there are newly formed minerals that contain hydrogen like serpentines. In those the amount of deuterium is higher by 2.5% compared with Archaean minerals.

The second source of Mother Earth's water loss is just the formation of minerals like serpentines incorporating hydrogen when magma reacts with water. When Pope and co-workers did the mathematics they concluded that oceans 3.8 Ga ago were more voluminous and that Mother Earth has lost 26% of its "light" water since then. Nowadays, however, both water leaks are less important than a trillion years ago for the chance of water reacting with magma is greatly reduced and the concentration of methane in today's upper atmosphere is much smaller than in Archaean times. We still lose 100 000 tons of hydrogen yearly diffusing into space. Does this mean that the Dutch no longer have to worry about rising oceans due to the melting of glaciers?

In 2009 UAF researcher Sebastian H. Mernild and colleagues from the United States, the United Kingdom and Denmark discovered that from 1995 to 2007, overall precipitation on the Greenland ice sheet decreased while surface ablation – the combination of evaporation, melting and calving of the ice sheet – increased. According to Mernild’s new data, since 1995 the ice sheet lost an average of 265 cubic kilometers per year, which has contributed to about 0.7 millimeters per year in global sea level rise. Last year this prediction became obsolete because Eric Rignot and co-workers jointly of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and the University of California, Irvine, reported that Polar ice sheet mass loss is speeding up, on pace for 1 foot sea level rise by 2050. The authors conclude that, if current ice sheet melting rates continue for the next four decades, their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050. When this is added to the predicted sea level contribution of 8 centimeters (3.1 inches) from glacial ice caps and 9 centimeters (3.5 inches) from ocean thermal expansion, total sea level rise could reach 32 centimeters (12.6 inches).

Compare this prediction i.e. more than 5 mm rise of the ocean level per year with the loss of water by leakage which only amounts to a fraction of a millimeter per year.

1 comment:

  1. Nice trick for Earth to take 3.7 TRILLION years to lose an Atlantic Ocean when the universe is only 14 BILLION years old. This blog is a cheap joke.