Snowball Earth: New study shows Antarctic climate even gripped the tropics

New study shows Antarctic climate even gripped the tropics
Welcome to your summer holidays, 750m years ago. Credit: Eli Duke, CC BY-SA

New details of a nightmare period on Earth with surface conditions as frigid as present-day central Antarctica at the equator have been revealed thanks to the publication of a study of ancient glacier water.

The research, by an international team led by Daniel Herwartz, is published in the journal Proceedings of the National Academy of Sciences and shows that even tropical regions were once covered in snow and ice.

In the most recent ice age, the last glacial advance (ending about 12,000 years ago) ice sheets extended across Europe at the latitude of southernmost England and reached south of the Great Lakes in North America. Beyond lay tundra, and so on – but the equatorial belt of tropical rainforest was still there. Much more drastic situations occurred far earlier in Earth's history however, and it is these that are supported by the new study. The periods have been dubbed "Snowball Earth".

This term first rose to prominence in the 1990s on the back of decades of geological observations of rocks deposited by glaciers, on land and at sea, during much of the period lasting from about 720m to 630m years ago at locations from across the globe which – at the time – were on the equator or no more than 40 degrees from it.

This was not easy for geologists to establish, because organisms that would leave large, easily recognisable fossils (so useful for relative dating) had not yet evolved. Moreover, the distribution of continents was different and has to be deduced by measuring traces of the Earth's magnetic field captured into the rocks when they formed (paleomagnetism). Over the period in question, a single super-continent known as Rodinia was beginning to break apart, but still straddled the equator.

Turning to snow

New study shows Antarctic climate even gripped the tropics
Rodinia contained most of the world’s continental crust. Credit: John Goodge, CC BY-NC-SA

Why the climate should ever veer so extremely as to become caught in Snowball Earth conditions is a complex matter. On the one hand the Sun was 20-30% fainter than it is now, and thus provided less heat. However, the ancient atmosphere had much more carbon dioxide in it than now, so there would have been a more effective "greenhouse effect" to trap heat and keep the planet warm.

Changes in the Earth's orbit, or in the tilt of its axis, might have tipped the balance – these are the likely cause of more recent glaciations – but it is possible that full Snowball Earth conditions can be initiated only when a super-continent lies across the equator. As land reflects more solar heat than the oceans, equatorial Rodinia maximised the amount of heat bounced back into space rather than absorbed into the seas and kept on Earth.

Snowball Earth conditions gripped Rodinia at least twice, in an older episode known as the Surtian and in a younger episode known as the Marinoan. Herwartz and his team studied rock samples from the Dabie-Sulu belt in modern day eastern China. Back in Surtian and Marinoan times this region was between 15 and 35 degrees north, the same sort of latitude as present-day Mexico, India or the Sahara.

The team also studied rocks from a much older proposed Snowball Earth episode, about 2.2 billion years ago, sampled in Karelia, in present-day northwest Russia close to the border with Finland. These too were at a low latitude at the time in question.0

Snowball hunting

New study shows Antarctic climate even gripped the tropics
Today you’ll have to go to Antarctica or Greenland to find a climate that chilly. Credit: Robert Rohde / NOAA / UEA, CC BY-SA

The researchers' key innovation was to analyse oxygen left behind by ancient glacial water as it reacted with rocks to form new minerals. They used this to work out the prevailing surface temperatures.

Oxygen comes in three stable forms, or "isotopes". Nearly 99.8% of oxygen atoms are oxygen-16 (made of 8 protons and 8 neutrons). Most of the remainder is oxygen-18 (8 protons and 10 neutrons), but there are also traces of oxygen-17 (8 protons and 9 neutrons).

A water molecule containing a heavier isotope of oxygen has the same chemical properties as a water molecule containing the lighter oxygen-16 but will evaporate less readily and condense more quickly. This means that the oceans lose containing oxygen-16 at a faster rate, and rain (or snow) falling far from the ocean will be poorer than average in the heaver isotopes. The ratios of the different oxygen isotopes in the recent geological past can be used as a proxy for global temperature, or to estimate how much water from the oceans has been removed and stored in glaciers.

It is far from simple to get at the information locked in ancient rocks of the kind studied by Herwartz's team, but by including the extremely rare oxygen-17 isotope in their study, they were able to show that both of the heavier isotopes must have been rarer than expected in the glacial water that had reacted with the rock. The difference in the depletion of oxygen-17 compared to the depletion in -18 enabled them to demonstrate likely mean annual surface temperatures of as much as 40°C below zero.

Such low temperatures imply that the oceans would have been deeply frozen too, supporting the full Snowball Earth model. But if the land where the rocks originated was so cold because it was several kilometres above sea level, the possibility that the planet was more of a Slushball Earth, with open seawater near the , cannot entirely be ruled out.


Explore further

Researchers find new information about 'Snowball Earth' period

More information: "Revealing the climate of snowball Earth from Δ17O systematics of hydrothermal rocks," by Daniel Herwartz et al. PNAS, DOI: 10.1073/pnas.1422887112

This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).
The Conversation

Citation: Snowball Earth: New study shows Antarctic climate even gripped the tropics (2015, April 14) retrieved 20 May 2019 from https://phys.org/news/2015-04-snowball-earth-antarctic-climate-thetropics.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.
66 shares

Feedback to editors

User comments

Apr 14, 2015
Wait, are you saying the Earth's climate changes as part of its normal life cycle?

STOP THE PRESSES! GET IT IN THE PAPER!

Apr 14, 2015
Wait, are you saying it will be okay to let the climate change to an extreme??


Apr 14, 2015
The Fifth Element is Boron. Just saying. this movie is so Boron I'm outta here.

Um, just means your gauge is broken man.

Gauge says minus a thousand. Just means it's broken man.

Now the Sun supposedly warms 10% per billion, but I wonder what the real stable temperature would be on Earth if you lowered Solar input by 10% indefinitely? That'd be some cooooolllld nights as a new equilibrium approaches. I think.

Imagine if the solar constant was 1200 instead of 1365. mahahahahahahahahahaha. Louisiana would be like Antarctica and Antarctica would be like Mars.

Maybe the Dinosaurs landed here on an Asteroid.

J.E.N.O.V.A.

Mama's boy time stopping bitch so easy, low level run....aw man i lost m FF7 license on my other computer.

*Sigh* Now I don't get to see an asteriod the size of a planet get blown away by the life force of all the dead people.

I don't know who's on more crack: American comic authors or Japanese game developers.

Apr 14, 2015
Like how Brainiac can process the thoughts of 7 octodecillion civilizations simultaneously. There's only a few hundred sextillion stars in the universe, so they'd have to all be type 2 civilizations with maximum populations in the duodecillions per star with like dyson spheres or something.

Now that's nonsense, but it was actually printed, and it's even more nonsense than the premise of Superman. I mean, if a person from a super-earth came to Earth they'd be really strong, not comic book strong, but then again the original Supes wasn't a galaxy buster either.

Okay, so the snowball Earth...

Hoo boy, this climate change snowballs and snowballs just like a comic book character's abilities keep inflating over time. Gotta top the last issue.

What if there was negative Kelvins? Oh my goodness how much would that screw up astronomy and physics. Negative kelvins. Maybe minus a thousand isn't broken after all. Maybe it's a different unit. Or maybe it's negative kelvins.

Apr 14, 2015
Noooo, not that damn animation again...

https://www.youtu...HB9J0eqs

Imagine watching this in a low level game for the first time you try a LLG without using someone's guide. He blows up the universe like 50 times during the fight.

It is settled.

The Japanese are on more crack.

Some kryptonite kills supes. Cloud's little dog is unphazed by the galaxy exploding from some inter-galactic collider moving faster than the speed of light to blow up the Sun.

*ahem*

Yes I'm aware that is unrealistic physics. What was your first clue?

who knows what the hell happened a billion years ago. Shit they can't even explain the Little Ice Age and the Younger Dryas.

Apr 14, 2015
I was disappointed you guys couldn't take a few jokes.

Apr 14, 2015
I was disappointed you guys couldn't take a few jokes.


@Returners

Considering your previous posts it would be difficult to tell if you were serious or joking around.

Apr 14, 2015
I was disappointed you guys couldn't take a few jokes.


You're in Colorado, right? I'm in Washington. Gotta watch out for the Posting Under the Influence. It's not really necessary to hit the "Submit" button in order to have a good time.

As Woody Allen once put it, "Laughs from pot smokers don't count."

Apr 15, 2015
"The ancient atmosphere had much more carbon dioxide in it than now, so there would have been a more effective "greenhouse effect" to trap heat and keep the planet warm."

" As land reflects more solar heat than the oceans, equatorial Rodinia maximised the amount of heat bounced back into space rather than absorbed into the seas and kept on Earth."
------------------------------------------------
Um... what?


Apr 19, 2015
Curious to know why Sol was 30% less luminous a mere 1/2 billion years ago. I theorize a magnetar sun which may periodically flare. A red dwarf flare. One 2 billion years ago melted Ice Ball Earth, then ebbed back to allow the ice to rule again, only to flare 1/2 b year ago? Less stronger as magnetars rapidly lose energy. Red dwarfs, on the other hand, are claimed to be limited to a smaller size than Sol hence have a cycle that goes into the core and back out utilizing all the fuel hence lasts forever. Proxima Centauri our closest neighbor is classified a red dwarf. Sol may have been losing luminosity after every flare event, perhaps the 65 my extinction event was a flare? That also heated the core? the 59 my PETM event?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more