Scientists have found the key to one of the Grand Canyon’s greatest mysteries

The walls of the Grand Canyon allow us to literally read the history of the Earth through the layers of rock.

But this record is incomplete.

In some places, very ancient crystalline rocks lie alongside much younger layers, whilst a vast part of the intervening geological history is missing.

This phenomenon is known as the Great Unconformity.

Put simply, the rocks that should have told the story of hundreds of millions, or even more than a billion, years of Earth’s history either failed to form or were destroyed by erosion.

And geologists have long been trying to understand what exactly could have removed such an incredible volume of rock.

Details

A team of researchers has suggested looking for the answer in the period when the supercontinent Rodinia broke apart.

Around 800 million years ago, the continent began to break apart. The western edge of ancient Laurentia — the core of what would become North America — was stretched, uplifted and gradually eroded.

According to the scientists’ calculations, a huge escarpment could have formed along the edge of the continent at that time — an extensive strip of steep cliffs up to approximately one kilometre high.

This was not a single ‘wall’ like a modern canyon, but a vast area of varying elevations capable of stretching for thousands of kilometres.

The most significant events took place after its formation.

Rivers, rainfall and other processes gradually eroded the steep slopes. The escarpment slowly retreated inland, and with it moved a zone of intense erosion.

Over tens of millions of years, colossal volumes of rock may have been removed from the surface.

According to researchers’ models, up to eight kilometres of rock may have been removed in some areas.

It was precisely this process that may have exposed the very ancient crystalline basement of North America — the rocks that can be seen today deep within the Grand Canyon.

According to the scientists’ reconstruction, the system of steep slopes may have extended across territories where Arizona, Utah, Idaho, Wyoming, Colorado, Texas, Oklahoma, Arkansas, Missouri and Illinois are located today.

However, the oldest of these terraces has long since disappeared.

Scientists have reconstructed its shape using models of tectonic plate movement and landscape evolution.

The researchers compared ancient North America with modern-day major escarpments in South Africa, Brazil and other regions. Such landscapes demonstrate how continental margins can slowly erode and retreat over tens of millions of years.

There is an important caveat here.

The new study does not claim that the Grand Canyon existed as far back as 800 million years ago.

The modern canyon formed much later and is closely linked to the development of the Colorado River system.

A gigantic ancient escarpment could have had another effect — removing a vast amount of rock in advance and bringing ancient layers to the surface.

Then, hundreds of millions of years later, the Colorado River carved its way through this landscape, exposing the geological history that we see today.

In other words, the scientists are proposing an explanation not for the origin of the canyon itself, but for why such a vast stretch of time is missing from its walls.

Previously, scientists had put forward various explanations for the Great Discontinuity.

One of these links large-scale erosion to ancient global glaciations — periods when the Earth may have been almost entirely covered in ice.

The new study adds another important factor to this picture.

The break-up of Rodinia may have created high, steep terrain that was particularly easy for rivers, glaciers and atmospheric processes to erode.

It is therefore not necessary to choose just one cause. Tectonic activity may have uplifted the rock and formed steep slopes, whilst climate and erosion may have gradually eroded them.

According to the authors, this vast terrain could have altered a much larger area.

The steep edge of Laurentia potentially influenced the course of rivers, sediment transport and which areas were later flooded by the sea.

Thus, this long-vanished system of cliffs may have shaped the development of North America’s landscape over tens of millions of years.

It existed long before the emergence not only of the modern Grand Canyon, but also of the complex life forms characteristic of the subsequent Cambrian period.

Why this is important

The Grand Canyon is unique not only in terms of its size. Its walls preserve nearly two billion years of Earth’s history — but this history is full of gaps.

New research proposes a mechanism that may explain one of the largest of these gaps.

If the model is confirmed by further research, the famous ‘missing billion years’ will turn out to be the result of events that began as far back as the break-up of the ancient supercontinent: a gigantic escarpment cut its way across the continent, allowing erosion to strip away kilometres of rock long before the Colorado River came into being.

Source

Study: Thomas M. Gernon et al. ‘Exhumation of the Grand Canyon’s basement along the Great Escarpment of Laurentia’.

Journal: Geology, 2026.