There were a billion years missing from Earth’s History. Mystery finally solved

The Great Unconformity, a gap in Earth’s geological record, has intrigued scientists for 150 years. A new study suggests it was created by the movement of tectonic plates, not Snowball Earths or Cambrian life.

The long-standing mystery of Great Unconformitya huge gap in the geological record that appears around the world and has fueled speculation for more than 150 years, has finally been resolved, according to a published this Monday in Proceedings of the National Academy of Sciences.

This unconformity manifests itself around the world when sedimentary rock around 500 million years old sits directly over “basement” rocks much olderwhich can often be more than 1.7 billion years old.

As missing layers can represent up to more than a billion years, making this characteristic “arguably the most iconic gapbut also more enigmatic, of the Earth’s stratigraphic record”, according to the authors of the new study.

Now, scientists led by Rong-Ruo Zhanfrom Northwest China University, presented new evidence that the gap was largely created by tectonic processes occurred between 2.1 billion and 1.6 billion years ago, in the Neoproterozoic era, during the formation of an ancient supercontinent called Columbia.

Their results, based on the study of geological sites in northern China, cast doubt on an alternative explanation which suggests that the gap was formed by a phase of “” — a widespread glaciation that occurred much later, between 700 and 600 million years ago.

This phase of glaciation closely preceded the Cambrian explosionone sudden proliferation of complex life around 530 million years ago it established the main animal groups, giving rise to theories that linked the two events.

The new study, with its revised chronology of tectonic processes, comes question this connection.,

“The contribution of this paper is to demonstrate that the exhumation of mid-crustal metamorphic and igneous rocks in northern China occurred mainly between 2.1 and 1.6 billion years ago, and that the timing of exhumation varies from continent to continent”, explains the co-author of the study Nicholas Christie-Blickprofessor at Columbia University’s Lamont-Doherty Earth Observatory.

“In other words, the surface may appear global, but its meaning varies,” he added. “The conclusion is therefore not surprising. It is very gratifying to have proved, in a previously less documented example (northern China), that chronology has no relation with the late Proterozoic glaciation (720 to 635 million years ago) nor with the emergence of animals in the Cambrian”.

The Great Unconformity is perhaps best known as a visible feature of the Grand Canyonwhich preserves the core of a long-vanished paleocontinent called Laurence. But it is also present in the remains of other paleocontinents, such as Baltica and the Amazon.

This is an extraordinary case of stratigraphic amnesiain which the Earth appears to have erased from memory entire epochs of geological timeand whose origin seems to have now finally been unraveled.