New Evidence Explains How A Global Glaciation Event Erased Part Of Earth’s Crust

Earth has been around for more than four billion years, but its surface doesn’t always tell the full story. Layers of rock should work like the pages of a history book, stacking over time and recording ancient oceans, volcanic eruptions, and even global disasters.

But for more than a century, scientists have known that a large portion of the geological “pages” was simply missing, and no one could agree on what happened to it. This mystery became known as The Great Unconformity, a baffling gap in the rock record where entire layers of Earth’s crust had vanished.

The issue wasn’t just a small patch here or there. It was global. In many places around the world, older rocks sit directly beneath much younger ones, with millions of years missing in between.

Now, researchers believe they’ve finally found the answer - and located where that lost material ended up. The story begins back in 1869, when geologists exploring the Grand Canyon noticed something strange.

At certain points along the canyon walls, rocks that were more than a billion years old were sitting right below rocks that were only a few hundred million years old. There was no gradual transition between eras. It was as if someone had ripped out a massive section of Earth’s timeline.

Scientists later found similar gaps in rock layers worldwide. This strange global pattern earned the name “The Great Unconformity.” But what could wipe away that much rock across multiple continents?

A Frozen Earth With a Violent Past

Recent studies now point to a dramatic event in Earth’s deep past: a period called Snowball Earth. During this time, which is believed to have occurred between 720 and 635 million years ago, glaciers may have covered nearly the entire planet, including the oceans.

Imagine ice sheets several kilometers thick grinding across the continents. Over millions of years, that kind of pressure could scrape away massive amounts of rock.

Dr. Brenhin Keller from the Berkeley Geochronology Center led one of the key studies investigating this theory. His team analyzed ancient mineral crystals, specifically looking for chemical signatures indicative of large-scale erosion. They found hafnium and oxygen isotopes that matched expectations for older rocks that had been ground down and redeposited by glaciers.

According to their calculations, glaciers may have removed an average of 3 to 5 kilometers (2 to 3 miles) of rock from the surface in many regions. Dr. Keller estimated that roughly one billion cubic kilometers, or about 200 million cubic miles, of rock from the pre-Cambrian era is currently missing from where it should be.

That’s not a small scratch; it’s geological devastation.

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So if glaciers scraped away billions of tons of rock, what happened to the debris? The study suggests that as glaciers advanced and retreated, they transported vast amounts of sediment toward the oceans.

Over time, this material settled on the seafloor and became part of marine sedimentary layers. In other words, the “missing” rock is likely lying beneath the oceans, buried and compressed into new formations.

This also helps explain another mystery: the lack of asteroid impact craters older than about 700 million years. If much of the Earth's surface from that time period was eroded away, the craters would have been wiped out with it.

Rewriting Earth's Geological Timeline

The findings suggest that erosion before the beginning of the Phanerozoic era (which started about 541 million years ago and includes the rise of animal life) was much more intense than previously believed.

It also shifts how scientists view Earth’s early history. Instead of a steady buildup of rock layers, the planet may have experienced violent periods of destruction that erased vast segments of geological time, only for new layers to build up afterward.

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After more than a century of speculation, evidence increasingly supports the idea that the Great Unconformity was carved out by glaciers during Snowball Earth. Dr. Keller and his colleagues believe the case is strong, but, as with most discoveries in science, it raises even more questions.

How exactly did these glaciers form? Were there multiple glaciation events involved? And how did Earth recover from being almost entirely frozen?

For now, though, one of Earth’s biggest geological mysteries finally seems to have a compelling explanation, and its missing pieces are probably resting quietly on the ocean floor.