Geoscientist Nicolas Flament of the University of Wollongong in Australia and his colleague Santosh Dhungana argue in a recent Nature study that slow currents of hot rock in Earth's mantle helped carve the Great Unconformity, a gap in the geologic record that can span more than a billion years of missing time.
The feature is visible in the Grand Canyon, where ancient crystalline rocks meet sandstones laid down as life started to diversify during the Cambrian explosion. “It's called the Great Unconformity, and it's a gap in the geologic record,” Flament said. “This gap can be anywhere between 200 million years, which is not that impressive, to more than a billion years.”
According to their models, the gap was carved with help from deep within the planet: slow currents of hot rock pushed entire continents up for hundreds of millions of years, letting glaciers grind them down and then letting them sink, allowing fresh sediments to bury the scar. The largest hole in the rock record, the researchers argue, might be a fingerprint of processes happening deep in the planet's interior.
The oldest sediments resting on the unconformity in North America are between 635 and 482 million years old, and geologists have traced it across most of North America and parts of northern Europe and northern China. "Something seems to have happened, in particular in North America," Flament said.
Analysis
Why This Matters
- The Great Unconformity is one of the most striking gaps in the rock record, removing hundreds of millions to more than a billion years of time in places; knowing how it formed tells geologists what happened to the continents during that lost interval.
- The study links a feature visible in canyon walls to mantle-scale movements, suggesting the planet's deep interior can leave fingerprints in the surface record.
- It offers a mechanism for why the gap is so pronounced in North America, where the oldest overlying sediments sit between 635 and 482 million years old.
Background
The Great Unconformity has puzzled geologists since the 19th century, when it was first described in the Grand Canyon, where flat-lying sedimentary layers rest directly on ancient crystalline rock. What removed the intervening rock has been debated ever since. The new study's models portray the missing time as the work of mantle-driven uplift and glacial erosion, followed by subsidence and fresh burial.
What to Watch
- How the modelling results are received by geologists who study the Great Unconformity's many exposures.
- Whether further dating of the sediments resting on the unconformity in North America, northern Europe and northern China supports the timing the model implies.
- Whether similar deep-Earth signatures show up where the unconformity has been traced on other continents.
Checked
11 claims in this story checked against 1 source: 10 supported.
Show each claim
- SupportedEarth’s churning mantle may have helped carve the Great Unconformity, the study argues.Science - Ars Technica: “In a recent Nature study, Flament and his colleague Santosh Dhungana argue that this gap was carved with help from deep within the planet.”
- SupportedA Nature paper links the rock record’s missing time to slow currents of hot rock deep inside Earth.Science - Ars Technica: “According to their models, slow currents of hot rock in Earth's mantle pushed entire continents up for hundreds of millions of years”
- SupportedGeoscientist Nicolas Flament of the University of Wollongong in Australia and colleague Santosh Dhungana argue this in a recent Nature study.Science - Ars Technica: “In a recent Nature study, Flament and his colleague Santosh Dhungana argue that this gap was carved with help from deep within the planet.”
- SupportedFlament said, “It's called the Great Unconformity, and it's a gap in the geologic record.”Science - Ars Technica: ““It’s called the Great Unconformity, and it’s a gap in the geologic record,” says Nicolas Flament”
- SupportedFlament said the gap can range from 200 million years to more than a billion years.Science - Ars Technica: “"This gap can be anywhere between 200 million years, which is not that impressive, to more than a billion years.””
- SupportedThe Great Unconformity is visible in the Grand Canyon, where ancient crystalline rocks meet sandstones deposited as life diversified during the Cambrian explosion.Science - Ars Technica: “In the Grand Canyon, there is a line in the rock where time seems to have gone missing. Ancient crystalline rocks mark its bottom, while sandstones laid down as life started to diversify during the Cambrian explosion mark the top.”
- SupportedAccording to the models, mantle currents pushed continents up for hundreds of millions of years; glaciers ground them down, then they sank and fresh sediments buried the scar.Science - Ars Technica: “According to their models, slow currents of hot rock in Earth's mantle pushed entire continents up for hundreds of millions of years, letting glaciers grind them down and then let them sink, allowing fresh sediments to bury the scar.”
- Partly supportedThe researchers argue that the largest hole in the rock record might be a fingerprint of processes deep inside the planet.Science - Ars Technica: “The largest hole in the rock record might be a fingerprint of processes happening deep in the planet's interior.”
- SupportedThe oldest sediments resting on the Great Unconformity in North America are between 635 million and 482 million years old.Science - Ars Technica: “The oldest sediments resting on the Great Unconformity in North America are between 635 and 482 million years old.”
- SupportedGeologists have traced the Great Unconformity across most of North America and parts of northern Europe and northern China.Science - Ars Technica: “Geologists have traced it across most of North America and parts of northern Europe and northern China.”
- SupportedFlament said, “Something seems to have happened, in particular in North America.”Science - Ars Technica: ““Something seems to have happened, in particular in North America,” Flament says.”