Rocks are like a time machine: they allow us to take a real dive into the past. The deeper we go into their layers, the older we find. Thanks to the study of rock layers and their intersections, we can discover a lot about the local geology and history of our planet, such as the phase of the planet in which it rained for 2 million years. Sometimes, however, scientists come across "unconformities": layers of overlapping rocks with a huge difference in age between them, and without intermediate layers.
An age-old mystery
In 1869 he was the geologist John Wesley Powell, exploring the Grand Canyon, to notice a huge age difference between the rock layers. Layers of rocks 1,4-1,8 billion years old were overlain by rocks “only” 520 million years old. This enormous gap in time, known as the Great Unconformity, has been found at other sites in North America and around the world, again with a billion years of missing history.
What could be the reason? There are several theories as to why this time gap occurs. A proposal in 2019, is linked to the so-called “snowball earth”. A period in which the Earth's surface would have completely frozen, from one pole to the other. According to this theory, the growth and retreat of glaciers would have eroded the rock layers and transported the material into the oceans, "subtracting" those that are now missing.
New discoveries and alternative hypotheses
In recent years, more recent studies tend to question this giant “snowball” theory. Research from 2020 analyzed rocks from Pikes Peak, Colorado, where older rocks rose to the surface before undergoing intense erosion about 717 million years ago. The hypothesis born from these analyzes is that the discrepancies observed throughout the world, although often dating back to the same period, are not caused by a single event.
“We are facing a similar phenomenon around the world, but in reality there may have been many Big Differences,” says the lead author of the 2020 study (that I link to you here), Dr Rebecca Flowers. “We should change the way we talk about the Great Unevenness if we want to think of it as a more complicated phenomenon, which arose at different times, in different places and for different reasons.” For example, the Great Unconformity found in North America was probably caused by the fragmentation of the supercontinent Rodinia 700-800 million years ago, which brought older rocks to the surface and dragged newer ones into the oceans.
The Great Nonconformity is a great setback
However you think, it is sad to think that we have lost so much information about our planet. Missing a billion years, no joke: it's like a giant amnesia, concludes a study Part 2021 about this phenomenon. Perhaps we will never be able to reconstruct what "happened to us" in all that time, and we will have to work in another way to steal from our planet the secrets that it jealously guards at the bottom of the sea, or in its core.
