The strange race to track down a missing billion years

Standing at the base of the cliffs and looking upwards, he could see a thick section of hard, crystalline rocks – mostly granite and schist (slate or shale that has been subjected to intense pressure), arranged in unusual vertical layers. Above this was a 1,000ft (305m) band of reddish sandstone, in the neat horizontal lines you would expect.

But here was the catch – by counting the layers of vertical crystalline rock, Powell estimated that this section should be 10,000ft (3,050m) thick. In reality, it measured just 500ft (152m). There were thousands of feet of missing rock – it had just vanished. He named this feature The Great Unconformity, and asked himself, "how can this be?".

Today geologists know that the youngest of the hard, crystalline rocks are 1.7 billion years old, whereas the oldest in the sandstone layer were formed 550 million years ago. This means there's more than a billion-year-gap in the geological record. To this day, no one knows what happened to the rocks in between.

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