I spent most of this past summer on Yale’s campus doing Earth science research. One of my main projects was focused on Snowball Earth. You may be wondering, what is Snowball Earth? Is it snowy? Is it edible? Can you throw it?
Well, once upon a time, a Caltech professor named Joe Kirschvink came across a strange rock sample — a sedimentary rock, old and crumbly, clearly layered. Kirschvink had long before made his name as a paleomagnetist, a geologist who specializes in analyzing the magnetization of old rocks. What does that mean? You can imagine the textbook diagram: Earth’s magnetic field lines curving over the globe from pole to pole. Turns out we can use those invisible magnetic field lines to interpret clues about the rock’s latitude during its formation. In other words, we can figure out how far from the equator the rock was formed based on some tests with magnets. (Shout-out to Dawn Sumner, a graduate of Caltech who worked on this rock for her senior thesis, and probably did a lot of the testing herself.)
Kirschvink’s strange rock sample was collected from an area known as the Elatina Formation, a unit in South Australia known to have glacial deposits. A long time ago, the area was associated with a shallow marine environment, probably along a coastline. Previous tests had already established that the rock had formed at some low latitude, near the equator. Finding both glacial deposits and an equatorial marine environment seemed to imply that at the time of formation, there were glaciers near the equator. And on further inspection, Kirschvink discovered that this formation spanned around a million years.
Let us pause for a moment and imagine what exactly this means. We have low-latitude glaciation, present for long periods in a marine environment. That indicates that at some point in Earth’s history, large ice sheets weren’t limited to alpine glaciers. So how much ice was there? We can imagine the last ice age, with ice sheets stretching from the North Pole all the way down into the northern parts of the United States (Long Island is a glacial deposit!), and for our purposes, let us take that ice sheet and extend it down to the equator. That would be…the entire Earth covered in ice, no? Hence the affectionate name, “Snowball Earth.”
Kirschvink was not the first to come across this outcrop or any Snowball Earth outcrop; people had been interested in formations like Elatina for almost a century, even if they hadn’t fully understood how these rocks had formed. But with advances in technology (and interest), scientists began realizing that this sort of outcrop could be found all over the world, from Australia to Canada to Namibia. Since Sumner’s work in 1987, a controversy surrounding this Snowball Earth has emerged in the scientific community. What exactly was this Snowball Earth like, and how long did these grand ice ages last?
This summer I worked on a model for Snowball Earth to interpret information that we glean from these mysterious rocks. As scientists say, the conditions of these glaciations are “badly constrained,” meaning we know little about what the Earth was like back then. For reference, we’re talking about more than 600 million years ago. This is before Sumner, before Kirschvink, before humanity, before dinosaurs, before most life as we know it even existed. Even with many geochemical analyses, as our efforts stand now, some aspects of Snowball Earth we can only imagine.
The results of my research? A secret. Just kidding — we’re still working on the model and fine-tuning it to fit some of the vague constraints that we have narrowed down. But here are some questions that the scientific community is wondering about:
If both land and ocean were iced over, how could any advanced forms of life have survived?
Was the Earth really completely covered in ice, or were there some exposed spots (such as a band of tropical waters at the equator)? Are total ice cover and survival of life mutually incompatible?
I would give you answers, but we still don’t know. In the meantime, you can be the scientist here, and if all this thinking about ice makes you cold, go outside and enjoy the summer while it lasts. Soon it will be cold. I promise Snowball Earth won’t happen anytime soon though, especially not with all of our carbon dioxide emissions these days. But that’s another story.
Rain Tsong is a senior in Morse College. Contact him at firstname.lastname@example.org.
(Featured image from Wikimedia.)