One of the greatest geological mysteries of planet, which has puzzled scientists since the 19th century, looks like it may finally have an explanation. It’s the phenomenon known as the Great Unconformity, in which about a billion years of geological history are missing from the rock record of Earth.

The phenomenon is particularly evident in the Grand Canyon of the United States, where Cambrian rocks lie directly on top of much older Precambrian rocks, leaving a huge gap in the Earth’s geological history, which spans some 4.6 billion years.

For decades, scientists have been trying to explain what caused this remote segment of geological history to disappear from the rock layers.

The two main theories

Until recently, there were two main explanations for the phenomenon.

The first was associated with the period known as the “Snowball Earth“, about 700 million years ago, when the Earth may have been almost entirely covered by ice. According to this hypothesis, extreme climatic conditions and geological processes could have eroded large portions of the rocks.

The second theory was related to the formation of the supercontinent Rodinia, about a billion years ago. The creation of this supercontinent is thought to have lifted ancient rocks to the surface, where they were exposed to erosion and gradually decayed.

Although both explanations were considered possible, neither could be definitively proven.

The new study

An international team of researchers now claims that the puzzle may have been solved thanks to the study of five geological regions in northern China, where the Great Dissonance phenomenon is also observed.

The research was published in the scientific journal Proceedings of the National Academy of Sciences.

The scientists analyzed radioactive elements in rocks below the discordance threshold to calculate how much time had passed since the rocks were cooled to specific temperatures.

The results showed that most of the erosion occurred long before the Snowball Earth period or the formation of Rodinia.

Supercontinent Columbia

Evidence suggests that the phenomenon is linked to an even older geological evolution: the formation of Columbia, Earth’s first true supercontinent, which formed about two billion years ago.

The researchers note that the most intense erosion recorded in the geological record appears to coincide with the development of this first supercontinent.

The study’s lead author, Liang Duan of Northwest University, told the journal Science that although the Snowball Earth period and the Rodinia supercontinent may have contributed to some extent, they are not the main cause of the disappearance of a billion years of geological history.

New questions about Earth’s history

But this new interpretation raises new questions about previous theories.

Previous research had linked the Great Divergence to a massive erosion event that enriched the oceans with nutrients and minerals, which likely contributed to the Cambrian eruption about 540 million years ago, when a wide variety of complex life forms emerged.

But the new dating shows that the main erosion occurred much earlier, during a geological period that scientists call the Boring Billion, the time between 1.8 and 0.8 billion years ago, which is considered relatively “quiet” from a geological point of view.

The new research, if confirmed by further studies, could change the way scientists understand the evolution of Earth’s geological history.