Imagine opening a history book and finding several chapters torn out. This was what geologists looking into the rock records of Earth’s past discovered on several continents in the 1870s.

They dubbed it the Great Unconformity. Where layers of rock often stack up in a steady sequence from oldest to youngest, in many places around the world there is a gap of hundreds of millions of years.

For 150 years, nobody has known what erased those missing chapters. In new research published today in Nature, we finally provide an explanation: deep processes inside Earth lifted some continents high above the sea, where their surfaces were scoured down by the grinding movement of enormous sheets of ice.

The Great Unconformity

Layers of rock often stack up in chronological order, with the oldest at the bottom and the youngest at the top.

Yet in some places, such as the Grand Canyon in North America, you can touch rock layers from two different ages, hundreds of millions of years apart. A flat layer of sedimentary rock, about 540 million years old or younger, rests directly atop a crystalline “basement” up to two billion years old.

Somewhere in between, a considerable chunk (up to a quarter) of Earth’s history has simply vanished.

Important........

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