The Earth's new water budget

March 5, 2012

Investigating the history of water on Earth is critical to understanding the planet's climate. One central question is whether Earth has always had the same amount of water on and surrounding it, the same so-called "water budget". Has Earth gained or lost water from comets and meteorites? Has water been lost into space? New research into the Earth's primordial oceans conducted by researchers at the Natural History Museum of Denmark at the University of Copenhagen and Stanford University revisits Earth's historical water budget. The results have just been published in the Proceedings of the National Academy of Sciences (PNAS) journal.

Water accounts for about ½ of a thousandth of the Earth's total mass, despite the fact that roughly 70% of the planet's surface is covered by this substance so vital to survival. Indeed, is a relatively "rare substance" on our "Blue Planet".

Where does water come from?

"One of the absolutely most intriguing things about Earth is that there are oceans of water and that the presence of liquid water has enabled the existence of life on Earth. Therefore, questions concerning how Earth got its oceans, where the water came from and – whether we are losing or gaining water from space – are fundamental questions in the understanding of the Earth's history," says Emily Pope of the Nordic Center for Earth Evolution at the of , University of Copenhagen.

Earth's "little bit" of water is divided among a variety of reservoirs. Therefore, a fairly accurate assessment of how much water currently exists on Earth can be made. But now, Emily Pope and her colleagues at the Museum of Denmark and Stanford University have also been able to determine that liquid water was also in existence upon the young Earth, billions of years ago. And, more consequentially, they have been able to approximate the ancient water budget.

The researchers have done this by examining 3.8 billion year old minerals from Greenland which are derived from the Earth's primordial oceans.

A "minor" loss

"We have managed to reconstruct the isotopic composition of 3.8 billion-year-old seawater using mineral samples from the Isua-rocks in Greenland. The results demonstrate that the young planet's oceans, in relation to those of today, had proportionately more "normal water" than "heavy water" in them. We can explain this difference by the fact that Earth has lost less than 1/4 of its water budget over the last roughly 4 billion years," says Pope.

It may sound like a lot of liquid, but it's a surprise for researchers that the Earth's water budget has been so relatively stable for so many years. The new findings concerning the historical development of oceans also support new theories and suggested solutions to "the faint young Sun paradox". Theories challenging the paradox were propounded by a number of researchers from the Natural History Museum of Denmark and Stanford in 2010.

About the faint early Sun paradox

In 1972, the late, world renowned astronomer and his colleague, George Mullen, formulated "the faint early Sun paradox." The paradox addressed the relative stability of the earth's over the 4.5 billion years of its existence in relation to the fact that during the same period, solar radiation has increased by 25-30 percent.

The paradoxical question that arose from the scientists was why the earth's surface, during the planet's infancy, was not covered by ice, when the sun's rays were much weaker than they are today. One possible solution to the paradox, among others, was proposed by the American atmospheric researcher Jim Kasting in 1993. He performed theoretical calculations which showed that 4 billion-years-ago, 30 percent of the Earths atmosphere was composed of CO2. The theory was that the impact of this large amount of greenhouse gas insulated the planet and prevented the oceans from freezing over.

An abundance of atmospheric CO2 however, was not the ice-limiting factor. Instead, a much thinner layer of cloud played a major role in keeping ice at bay. Furthermore, the was covered by ocean. This meant that the Sun's relatively unimpeded rays could warm the massive ocean which in turn could store heat and prevent the freezing of its surface, according to the research group from University of Copenhagen and Stanford. This is their current answer to the long-standing riddle.

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not rated yet Mar 05, 2012
I'm sorry, I don't think I read that correctly.

They are saying at one point in time (although early) we had possibly 30% of the Earth's overall atmosphere as being CO2? At its Current levels, the Earth's atmosphere is approximately 0.04% CO2.

This requires more data and research! Its fascinating to think that at one point the CO2 could have been that high. How did it get down to its current levels?
not rated yet Mar 05, 2012
For some reason I cannot edit the post I just made. I wanted to add...

YES, I know its theoretical! But that doesn't makes those numbers any less fascinating. Even if the Earth's Atmosphere was previously only 1% CO2, it'd still be highly interesting to see the theories of how it got down to its current /-0.04% levels.
5 / 5 (1) Mar 05, 2012
For some reason I cannot edit the post I just made. I wanted to add...

YES, I know its theoretical! But that doesn't makes those numbers any less fascinating. Even if the Earth's Atmosphere was previously only 1% CO2, it'd still be highly interesting to see the theories of how it got down to its current /-0.04% levels.

5 / 5 (3) Mar 05, 2012
Most of the Earth's surface carbon is in carbonate minerals, such as limestones. These form through either erosion or biological action, from calcium, magnesium, sodium, and other metals. Early in Earth's history there would have been few if any carbonates, so the carbon was in the air as CO2. Carbonates decompose at moderately high temperatures, so if the surface was a hot as Venus, it would all go BACK to CO2, and we'd have an atmosphere similar to Venus.

If the air had no CO2, water alone wouldn't provide enough greenhouse effect to keep the oceans liquid, carbonate formation would cease, and volcanoes would increase atmospheric CO2. If the world gets too warm, evaporation, rainfall, and erosion increase, and CO2 levels drop. Left alone, the surface remains just above freezing.
1 / 5 (6) Mar 05, 2012
The idea that all that early CO2 went into carbonate rocks is really just one of those "lies" that are told to support the current paradigm, but has no real basis in fact.
Kind of like subduction, subduction zones account for a very small amount of all plate boundaries compared to spreading centers. Yet we are supposed to believe that all that crust has been drawn down into just a tiny percentage of fault zones.
I'd love to see where anyone has actually done the surveys and math necessary to support this, but so far I'm not aware of that actually having been done.
2.6 / 5 (5) Mar 05, 2012

Under the most common models of Earth's interior, once the radio isotopes passed the peak decay rate, the earth's mantel and core should always be in net cooling and contracting over the long term.

There is room for significant re-heating due to gravitational potential energy, which is converted to heat as the planet continues to contract, but this is limited by the maximum density of the Earth.

Beyond radioactivity, there is no other proven mechanism for the Earth to transmute matter internally, so it should obey simple thermodynamic and gravitational laws. Which means the radius should shrink gradually over time. Meteor dust is negligible at this point.

On the other hand, if some exotic nuclear physics is possible at Earth core pressures, then all bets are off, as we have no way of directly testing any such hypothesis.

i.e. if Rossi's Nickel reactor works, then maybe the Earth can fuse Nickel in it's core or mantel...just silly though...
2.6 / 5 (5) Mar 05, 2012
If the Earth contracted by 1% in a period of 420 million years, it would convert the difference in gravitational potential to heat at a rate of 1 Watt per square meter for the duration of the "cooling" event.

That would reduce the radius by about 0.15mm per year.

In reality, it contracts much slower than that, I'm sure.

Our GPS system would be able to detect that rate of change over time periods of perhaps 20 to 30 years.

Also, the "weight" of a kilogram would seem to grow gradually over time, as the planet's radius contracts by a microscopic amount each year, but the difference in the "weight" of a kilogram would only be a matter of 1 point in the 35th decimal place each year, if the Earth were contracting in radius at 0.15mm per year...
5 / 5 (4) Mar 05, 2012
Stillwind: The amount of crust subducted HAS to equal the amount created, or the volume of the Earth would change. Where would the difference come from or go to? Besides, most of the subducted crust isn't IN the subduction the trenches, it's under the adjacent plate, slowly melting, before returning to the surface through volcanoes.
2.6 / 5 (5) Mar 05, 2012
I'm sorry, I don't think I read that correctly.

They are saying at one point in time (although early) we had possibly 30% of the Earth's overall atmosphere as being CO2?

Yes, and the other major gases were nitrogen water vapor, hydrogen chloride and carbon monoxide. They were mostly derived from planetary outgassing and volcanism and also from cometary impacts.

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