Ancient tectonic activity was trigger for ice ages, study says

Continental shifting may have acted as a natural mechanism for extreme carbon sequestration
“Everybody agrees that on geological timescales over hundreds of millions of years, tectonics control the climate, but we didn’t know how to connect this,” says Oliver Jagoutz. Credit: Christine Daniloff/MIT

For hundreds of millions of years, Earth's climate has remained on a fairly even keel, with some dramatic exceptions: Around 80 million years ago, the planet's temperature plummeted, along with carbon dioxide levels in the atmosphere. The Earth eventually recovered, only to swing back into the present-day ice age 50 million years ago.

Now geologists at MIT have identified the likely cause of both ice ages, as well as a natural mechanism for carbon sequestration. Just prior to both periods, massive tectonic collisions took place near the Earth's equator—a tropical zone where rocks undergo heavy weathering due to frequent rain and other environmental conditions. This weathering involves chemical reactions that absorb a large amount of from the . The dramatic drawdown of carbon dioxide cooled the atmosphere, the new study suggests, and set the planet up for two ice ages, 80 million and 50 million years ago.

"Everybody agrees that on geological timescales over hundreds of millions of years, tectonics control the climate, but we didn't know how to connect this," says Oliver Jagoutz, associate professor of Earth, Atmospheric and Planetary Sciences (EAPS) at MIT. "I think we're the first ones to really link large-scale tectonic events to climate change."

Jagoutz and his colleagues, EAPS Professor Leigh Royden, and Francis McDonald of Harvard University, have published their findings today in the Proceedings of the National Academy of Sciences.

Continental shifting may have acted as a natural mechanism for extreme carbon sequestration
The Nidar Ophiolite in Northeast India is a piece of rock formed in a long-gone ocean that separated India and Eurasia. A new study suggests that when tectonic forces emplace such ophiolites onto continents at low latitude, the weathering of these rocks can pull a large amount of carbon dioxide out of the atmosphere. Credit: Oliver Jagoutz
Putting the squeeze on

The two tectonic collisions that the team studied stemmed from the same event: the slow northward migration of Gondwana, a supercontinent that spanned the Southern Hemisphere from 300 million to 180 million years ago and eventually broke up to form Antarctica, South America, Africa, India, and Australia.

Around 180 million years ago, tectonic activity began to push fragments of Gondwana up toward the northern supercontinent of Eurasia, which slowly squeezed and eventually closed the Neo-Tethys Ocean, an ancient body of water lying between the supercontinents.

In previous work, Jagoutz and his colleagues developed a model to simulate the tectonic shifting that occurred in and around that ocean as Gondwana fragments were crushed against Eurasia. Through analysis of ancient rocks in today's Himalayas, the team determined a sequence of events as the continents merged.

They found that 90 million years ago, the northeastern edge of the African plate collided and slid under an in the Neo-Tethys Ocean, creating a chain of volcanoes. At 80 million years ago, as Africa continued advancing north, the oceanic plate was pushed further up and over the continent, exposing ocean to the atmosphere, while simultaneously terminating the volcanoes. Then, 50 million years ago, India merged with Eurasia in a second collision in which a different region of the oceanic plate was pushed up onto that continent.

Both collisions took place in the Intertropical Convergence Zone (ITCZ), an atmospheric region hovering over the Earth's equator, in which trade winds come together to generate a region of intense temperatures and rainfall.

A weathering trigger

For this new paper, the researchers wondered whether the tectonic collisions in this extremely tropical region may have played a part in pulling huge amounts of carbon dioxide out of the atmosphere and triggering the ice ages.

Certain types of rock, if exposed to high heat and heavy rain, undergo chemical reactions and effectively absorb carbon dioxide, a process known as silicate weathering. These rocks include basalts and "ultramafic" rocks, which are often found within oceanic plates. If these rocks are exposed to the atmosphere in a tropical region, they can act as very efficient carbon sinks.

The team hypothesized that the two collisions, involving Africa and then India, brought basaltic and up from the oceans and onto land, creating carbon sinks 80 and 50 million years ago. Both collisions also effectively turned off carbon sources by burying volcanoes that had been emitting carbon dioxide and other gases into the atmosphere.

To know whether such a sequence of events directly reduced carbon dioxide in the atmosphere, the researchers looked to weathering rates of different rock types, including granites, basalts, and ultramafics. These rates, which have been calculated by other researchers, describe the way rocks erode and take up carbon dioxide, given exposure to a certain amount of rainfall.

They then applied these weathering rates to their model's estimates of the amount of oceanic plate that was pushed up onto Africa and India, at 80 and 50 million years ago, respectively. After determining the amount of carbon dioxide sequestered by these rocks, they calculated the total amount of atmospheric carbon dioxide through time, from 100 million years ago to around 40 million years ago.

The team found that carbon dioxide dipped dramatically at precisely the time the two collisions occurred. The levels of carbon dioxide also mirrored the temperature of the oceans during this interval.

Jagoutz says one reason these two collisions had such an extreme effect on may have been the fact that each continent continued moving north, exposing new basaltic and ultramafic material, "like a bulldozer that brings fresh rock to the surface."

Interestingly, a similar process is taking place today, albeit at a smaller scale, near the island of Java. The same that shifted Gondwana northward more than 100 million years ago is today pushing the Australian plate north, and as a result, is piling up basaltic material on Java within the ITCZ, which Jagoutz says is "a huge carbon sink."

"What nature shows us is, if you put a lot of these rocks in the tropics, where it's hot, muggy, wet, and rains every day, and you also have the effect of removing the soil constantly by tectonics and thus exposing fresh rocks, then you have an excellent trigger for ice ages," Jagoutz says. "But the question is whether that is a mechanism that works on the timescale that is relevant for us."

"To confidently estimate the long-term fate of fossil fuel carbon in the atmosphere, we need to fully understand the dynamics of the carbon cycle and how it operates on all time scales," says Lee Kemp, professor of geosciences at Penn State University. "This study highlights an important restorative force of the carbon cycle. The 'repair mechanism' for volcanism-induced warming is the chemical weathering of the volcanic rocks themselves—a repair job that takes millions of years."


Explore further

Researchers explain mystery of India's rapid move toward Eurasia 80 million years ago

More information: Oliver Jagoutz et al. Low-latitude arc–continent collision as a driver for global cooling, Proceedings of the National Academy of Sciences (2016). DOI: 10.1073/pnas.1523667113
Citation: Ancient tectonic activity was trigger for ice ages, study says (2016, April 19) retrieved 24 May 2019 from https://phys.org/news/2016-04-ancient-tectonic-trigger-ice-ages.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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Apr 19, 2016
Well wont that require a new theory of heavier oceanic basalts climbing up and over lighter continental rocks?

Apr 19, 2016
@katesisco: It was continents that plowed into each other. That would mean the usual subduction scenario no longer applies. I would think of a thin piece of plastic that is compressed. Part will go down but part will go up when it folds over.

Apr 19, 2016
It's astonishing such garbage gets past peer review. How does this fit with the near perfect cyclical nature of the ice ages?

Apr 19, 2016
antigoracle - are you comparing the ice ages cycles of 10s of thousands of years over the last 400k year period to a process that occurs in periods of 10s of millions years?

Apr 19, 2016
80 mya is kinda smack dab in the middle of the Cretaceous. How did dinos survive that?

Apr 19, 2016
This seems a very odd paper not upon anything Pleistocene, the Miocene was warmer than the Pliocene where our CO2 level is today continuing to cool into what's termed the "ice-ages" of the Plieistocene via rock weathering CO2 reductions.

I fail to get how it relates to the title, it's all so misleading in our modern context like Snowball Earth, ok yet CO2 was higher then, zero connection to today's thermal position that was before the Southern Ocean was open and the Isthmus of Panama closed ??

Apr 19, 2016
80 mya is kinda smack dab in the middle of the Cretaceous. How did dinos survive that?

They had several million years to adapt.

Apr 19, 2016
antigoracle - are you comparing the ice ages cycles of 10s of thousands of years over the last 400k year period to a process that occurs in periods of 10s of millions years?

Probably. He doesn't understand much about science.

Apr 20, 2016
80 mya is kinda smack dab in the middle of the Cretaceous. How did dinos survive that?

They had several million years to adapt.

Reptiles today haven't managed to maintain that ability, it appears...

Apr 20, 2016
80 mya is kinda smack dab in the middle of the Cretaceous. How did dinos survive that?

They had several million years to adapt.

Reptiles today haven't managed to maintain that ability, it appears...

Well reptiles aren't dino's either. Did you mean reptiles?

Reptiles today are having to adapt in a couple of hundred years. Some might, many won't.

Guess I'm not sure what you're driving at WG.

Apr 20, 2016
"How did dinos survive that?"

Good question!

Some of them lived on continents hat weren't as cold.

Some did, and there is evidence from Australia of dinosaurs surviving well into areas changing into temperate climates that had snow in the winters. Some dinosaurs were massive so could retain heat as grown and displayed herding behavior (as some mammals and avian dinosaurs do today to keep their young protected).

Others likely mostly grew their feather protection; as we know from today the hardiest avian dinosaurs survive Antarctic temperatures. Avian dinosaurs split before that (~110 Myrs, IIRC), so that wasn't why they evolved. But it likely increased their diversity.

Admittedly, those were outliers. Dinosaurs evolved in tropical climates and their diversity tended to shrink in other climate zones. We know from recent results that the large clades - except avians - were decreasing that way (diversity going down) at the time, so maybe that was a factor.

Apr 20, 2016
80 mya is kinda smack dab in the middle of the Cretaceous. How did dinos survive that?

They had several million years to adapt.

Reptiles today haven't managed to maintain that ability, it appears...

Well reptiles aren't dino's either. Did you mean reptiles?
Reptiles today are having to adapt in a couple of hundred years. Some might, many won't.

Guess I'm not sure what you're driving at WG.

Apparently, I was under the impression dino's were reptilian...
It just seemed to me that in an ice age, the whole planet lost heat to some degree (pun intended). Therefore, cold blooded species (reptiles) suffered..

Apr 20, 2016
Apparently, I was under the impression dino's were reptilian...
It just seemed to me that in an ice age, the whole planet lost heat to some degree (pun intended). Therefore, cold blooded species (reptiles) suffered..
- WG
Not the WHOLE planet. There were pockets of land mass, particularly in the mid-latitudes, that were still warm enough to support animal and plant life, such as the ancestors of the lemurs and shrews. There was a lot of island building in the oceans, so that the heat from volcanos helped to warm the atmosphere in tropical areas from the warm winds. If that wasn't the case, then the early apes and their own ancestors (whom homo sapiens is purported to descend from), would have gone the way of the dinosaurs also. Cold-blooded lizards, such as Gila Monster, Komodo Dragon, Iguana, Gecko, Chameleon, and others also survived. possibly because of their smaller size and their smaller food requirements.

Apr 20, 2016
What we need on this science forum is a great consensus builder who can announce the Final Word on the outcome: Al Gore.........that great scientist who has a degree in "Government", Harvard 1969. If you take a look at a Harvard 1969 Catalogue under "Government", no math or science courses. BUT WHO CARES, he's a friend in high places (when he's smoking weed).

Apr 20, 2016
This strikes me as an alternative or supplementary theory to the one about the arrangement of the continents blocking equator-to-pole currents in the oceans leading to ice ages.

Apr 20, 2016
80 mya is kinda smack dab in the middle of the Cretaceous. How did dinos survive that?
No kidding- what "ice age" 80 mya? There isn't even a blip in the extinction rate. I'm skeptical. I'd need to see some evidence of this supposed "ice age."

The next big extinction is the one that was supposed to be due to the Chixulub event, and that's 20 million years later at about 60 mya.

Apr 20, 2016
Not the WHOLE planet. There were pockets of land mass, particularly in the mid-latitudes, that were still warm enough to support animal and plant life.

Even those must have experience cooling to some degree. Just not as much as elsewhere...
There was a lot of island building in the oceans, so that the heat from volcanos helped to warm the atmosphere in tropical areas from the warm winds.

Nope. Not buyin' that one. Cooling effect from particle clouds reflecting a lot of solar input.
If that wasn't the case, then the early apes and their own ancestors (whom homo sapiens is purported to descend from), would have gone the way of the dinosaurs also.

Stll got plenty of time for that...:-)
Cold-blooded lizards, such as Gila Monster, Komodo Dragon, Iguana, Gecko, Chameleon, and others also survived. possibly because of their smaller size and their smaller food requirements.

Reasonable.

Apr 20, 2016
80 mya is kinda smack dab in the middle of the Cretaceous. How did dinos survive that?
No kidding- what "ice age" 80 mya? There isn't even a blip in the extinction rate. I'm skeptical. I'd need to see some evidence of this supposed "ice age."

Kinda what I was hinting at...

Apr 20, 2016
/me is staring at the Wikipedia article on the "Cretaceous Thermal Maximum." And wondering what the heck these people are talking about with their "ice age" 80 mya.

Apr 20, 2016
OK, figured it out.

There wasn't any "ice age" after these events 80 mya. There was a CO₂ drawdown that terminated the Cretaceous Thermal Maximum, not an "ice age."

The second CO₂ drawdown ~50 mya terminated the Eocene Thermal Maximum, and eventually- perhaps, after a very long time- led to the current ice age. Maybe.

This article is badly written. I might even say very badly. The abstract of the paper makes that clear.

Apr 21, 2016
It's astonishing such garbage gets past peer review. How does this fit with the near perfect cyclical nature of the ice ages?


Naa you're off track, what is astonishing is that you can't even read peer reviewed science let a lone understand it, commenting about it by you is hilarious... :D here monkey monkey have another banana... ;)

Apr 21, 2016
antigoracle - are you comparing the ice ages cycles of 10s of thousands of years over the last 400k year period to a process that occurs in periods of 10s of millions years?

Probably. He doesn't understand much about science.

everyone knows that, with each try he gets even dumber.... lol... :D C'mon antisciencegorilla bonobo, lets have another sock of your's giving his monkey thoughts... ;)

Apr 24, 2016
As I read this article I was wondering what the Christians and Moslems would make of it. Then I read the comments and I see they just don't accept any of the arguments made. And It seems to me they will make up any excuse to denigrate the research because, after all, the world is less than 10,000 years old and any research that indicates anything else is just rubbish.

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