More 'reactive' land surfaces cooled the Earth down

More 'reactive' land surfaces cooled the Earth down
Zermatt in the Western Alps. Credit: F. von Blanckenburg

There have been long periods of cooling in Earth's history. Temperatures had already fallen for more than 10 million years before the last ice age began about 2.5 million years ago. At that time, the northern hemisphere was covered with massive ice masses and glaciers. A geoscientific paradigm, widespread for over 20 years, explains this cooling with the formation of the large mountain ranges such as the Andes, the Himalayas and the Alps. As a result, more rock weathering has taken place, the paradigm suggests. This in turn removed more carbon dioxide (CO2) from the atmosphere, so that the greenhouse effect decreased and the atmosphere cooled. This and other processes eventually led to the ice Age.

In a new study, Jeremy Caves-Rugenstein from ETH Zurich, Dan Ibarra from Stanford University and Friedhelm von Blanckenburg from the GFZ German Research Centre for Geosciences in Potsdam were able to show that this paradigm cannot be upheld. According to the paper, weathering was constant over the period under consideration. Instead, increased reactivity of the land surface has led to a decrease in CO2 in the , thus cooling the Earth. The researchers published the results in the journal Nature.

A second look after isotope analysis

The process of weathering, and especially the chemical weathering of rocks with , has controlled the Earth's climate for billions of years. Carbonic acid is produced from CO2 when it dissolves in rainwater. Weathering thus removes CO2 from the Earth's atmosphere, precisely to the extent that volcanic gases supplied the atmosphere with it. The paradigm that has been widespread so far states that with the formation of the large mountains ranges in the last 15 million years, erosion processes have increased—and with them also the CO2-binding rock weathering. Indeed, geochemical measurements in ocean sediments show that the proportion of CO2 in the atmosphere has strongly decreased during this phase.

More 'reactive' land surfaces cooled the Earth down
Soil formation in the Chilean coastal mountains. The soil is already heavily weathered, but granite blocks remain and can react chemically: The 'reactivity' of this soil is high. Credit: F. von Blanckenburg, GFZ

"The hypothesis, however, has a big catch," explains Friedhelm von Blanckenburg of GFZ. "If the atmosphere had actually lost as much CO2 as the weathering created by erosion would have caused, it would hardly have had any CO2 left after less than a million years. All water would have had frozen to ice and life would have had a hard time to survive. But that was not the case."

That these doubts are justified, was already shown by von Blanckenburg and his colleague Jane Willenbring in a 2010 study, which appeared in Nature likewise. "We used measurements of the rare isotope beryllium-10 produced by cosmic radiation in the Earth's atmosphere and its ratio to the stable isotope beryllium-9 in ocean sediment to show that the weathering of the land surface had not increased at all," says Friedhelm von Blanckenburg.

More 'reactive' land surfaces cooled the Earth down
The 'reactivity' of the land surface. If there are more non-weathered mineral grains such as feldspar or mica in the soil, it can react as extensively chemically with little CO2 as an already heavily weathered soil with a lot of CO2. Credit: CC-BY 4.0: F. von Blanckenburg, GFZ

The land's surface has become more reactive

In the study published now, Caves-Rugenstein, Ibarra and von Blanckenburg additionally used the data of stable isotopes of the element lithium in as an indicator for the weathering processes. They wanted to find out how, despite constant rock weathering, the amount of CO2 in the atmosphere could have decreased. They entered their data into a computer model of the global carbon cycle.

Indeed, the results of the model showed that the potential of the land surface to weather has increased, but not the speed at which it weathered. The researchers call this potential of weathering the reactivity of the land surface. "Reactivity describes how easily chemical compounds or elements take part in a reaction," explains Friedhelm von Blanckenburg. If there are more non-weathered and therefore more reactive rocks at the surface, these can in total react as extensively chemically with little CO2 in the atmosphere as already heavily weathered rocks would do with a lot of CO2. The decrease in CO2 in the atmosphere, which is responsible for the cooling, can thus be explained without an increased speed of weathering.

"However, a geological process is needed to rejuvenate the land surface and make it more reactive," says Friedhelm von Blanckenburg."This does not necessarily have to be the formation of large mountains. Similarly, tectonic fractures, a small increase in erosion or the exposure of other types of rock may have caused more material with potential to show at the . In any case, our new hypothesis must trigger geological rethinking regarding the cooling before the last ice age."

Explore further

Unlocking earth's climate past: A new tracer identifies weathering intensity over time

More information: Neogene cooling driven by land surface reactivity rather than increased weathering fluxes, Nature (2019). DOI: 10.1038/s41586-019-1332-y ,
Journal information: Nature

Citation: More 'reactive' land surfaces cooled the Earth down (2019, July 3) retrieved 21 October 2019 from
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User comments

Jul 03, 2019
What about the differences in weathering from acid rain years versus the current lack of acid rainfall?

Jul 03, 2019
The complete and utter bullshit of AGW Cult "science", all to sustain their dogma.

Jul 03, 2019
Good news and "bad" news.

The good news is that it won't affect climate models from 2.5 Myrs ago and on, and those are very precise.

The "bad" news is that climate science denialists will have an even worse time explaining why the current extreme warming rate is not unique. Earlier times are less comparable and there are more factors in heaven and earth than are dreamt of in their "philosophy".

Jul 03, 2019
The "good" news is that the AGW Cult's Chicken shites for brains will continue to confirm what idiots their cult takes them for.
And so, they will never see that as the earth came out of the Little Ice age, it warmed faster from 1910 to 1945 when anthropogenic CO2 was insignificant to that of the last 50 years.

Jul 04, 2019
oh deer, somebody let auntieoral out of her playpen

she's dribbling denialist kool-aid all over the keyboard

& while you're putting her back?
for gods sake, change her diaper!

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