Deep in the canyon walls of Arizona, the rock record breaks off mid-sentence: layers from the Cambrian sit directly upon basement stone that may be two billion years old, with a vast span of Earth's history simply absent. Geologists have pondered this silence since the 1870s, and now a pair of researchers at the University of Wollongong have offered an account that has been tested rather than merely imagined. Their answer is one of patient motion beneath the surface, in which ancient continental cores rose and later sank, and in doing so gave up the very pages that would have told the missing
Sinking Ancient Continents May Explain Earth's 150-Year-Old 'Missing Pages' Geological Gap
These pages weren't lost by chance.
Mark
Why does a gap in the rock matter so much?
Mimi
Because it hides a huge stretch of Earth's history. At the Grand Canyon, rock from about 540 million years ago or younger sits right on basement that could be two billion years old.
Mark
And the new explanation is what, exactly?
Mimi
Ancient continental cores rose in the Neoproterozoic, then sank over the last 540 million years. The rising let erosion strip rock away, and the sinking buried the worn surface.
Luke
Let me be careful here. This is a model, not a core sample. The simulation shows that the process can produce the gap, which is not the same as proving it did.
Mimi
Fair. But the report says it was tested against how the Earth behaved over time, which few earlier ideas were.
Mark
Which regions does it cover?
Mimi
North America, northern Europe and northern China.
Luke
Worth noting that the report doesn't say whether it explains unconformities elsewhere, or how other researchers have responded. That's unknown so far.
Mark
What about the computing side?
Mimi
Each simulation took about 75,000 CPU hours on Gadi. That's the scale needed to model the mantle.
Luke
Publication in Nature signals peer review, but the article offers no outside reaction, so I'd treat this as one team's well-tested proposal.
O Pulso
- A strange seam runs through the Grand Canyon, where sediments roughly 540 million years old rest on rock up to two billion years old, and the time between them has vanished.
- For about 150 years, geologists have circled an absence that resists direct observation, making every explanation hard to confirm or refute.
- Researchers at the University of Wollongong turned Australia's Gadi supercomputer loose on mantle convection simulations, each consuming around 75,000 CPU hours, to test the competing theories against Earth's behaviour.
- The models point to the cores of North America, northern Europe and northern China rising in the Neoproterozoic, then sinking into the ocean and burying their eroded surfaces.
- The work now sits in Nature as a tested explanation, and it is expected to shape how geologists read the rock record from here.
Deep in the canyon walls of Arizona, the rock record breaks off mid-sentence: layers from the Cambrian sit directly upon basement stone that may be two billion years old, with a vast span of Earth's history simply absent. Geologists have pondered this silence since the 1870s, and now a pair of researchers at the University of Wollongong have offered an account that has been tested rather than merely imagined. Their answer is one of patient motion beneath the surface, in which ancient continental cores rose and later sank, and in doing so gave up the very pages that would have told the missing story.
In the walls of the Grand Canyon in Arizona, a strange join runs through the rock. Sedimentary layers from about 540 million years ago sit directly on basement rock that may be up to two billion years old, and whatever should lie between them is simply not there. Geologists have known about gaps like this since the 1870s, when the Great Unconformity was first identified across the globe.
For decades, many explanations were offered, but the evidence was an absence, which made them hard to test. Associate Professor Nicolas Flament and PhD candidate Santosh Dhungana set out to check them against how the Earth actually behaved over time. Using Gadi, one of Australia's most powerful supercomputers, they ran mantle convection models, simulations of the slow movement of the Earth's interior and its effect on the surface.
Their results showed that the ancient cores of North America, northern Europe and northern China rose during the Neoproterozoic, then subsided through the Phanerozoic. As they sank, the worn rock surface was buried, forming the gap. Flament compared it to a single long uplift followed by a long sinking, which strips rock away and then preserves what remains. Dhungana offered an image of a book with a section torn from its middle. The research suggests those pages were not lost by chance, and as Flament noted, what is missing can tell us as much about Earth's story as what can be seen.
In the walls of the Grand Canyon in Arizona, a strange join runs through the rock. Sedimentary layers from about 540 million years ago, or younger, sit directly on top of ancient basement rock that may be up to two billion years old. Whatever should lie between them is simply not there. Geologists have known about gaps like this for roughly 150 years, and now two researchers at the University of Wollongong say they have a tested explanation.
The gap is called the Great Unconformity, first identified in the 1870s. Rock layers normally stack in order, oldest at the bottom and youngest on top. But across the globe, geologists have found places where sedimentary rocks from the Cambrian period, which marks the explosion of animal life 540 million years ago, rest directly on rocks more than a billion years old. Huge spans of time are missing from the record.
Many people have theorised about why. The difficulty is that the evidence is an absence, which makes hypotheses hard to test. Associate Professor Nicolas Flament said that few of the many proposed explanations had been checked against how the Earth actually behaved over time.
He and PhD candidate Santosh Dhungana set out to do that using Gadi, one of Australia's most powerful supercomputers. They ran mantle convection models, simulations of the slow movement of the Earth's interior and its effect on the surface. Each simulation took about 75,000 core-processing, or CPU, hours to finish.
Their model showed that the ancient cores of North America (known as Laurentia), northern Europe (Baltica) and northern China rose during the Neoproterozoic Era, between one billion and 540 million years ago. Those cores then subsided during the Phanerozoic eon, the past 540 million years. As they gradually sank into the ocean, the worn rock surface was buried, forming the Great Unconformity. The work, published in the journal Nature, describes the gap as the product of continental-scale erosion of ancient crystalline basement.
Flament described the sequence in terms of what it does to rock. A single long period of uplift followed by a long period of sinking, he said, would have been the ideal recipe for removing the rock and then preserving the eroded surface. Uplift exposes the rock to be stripped away, and subsidence buries what remains.
Dhungana offered an image of the problem: a book with a huge section torn out of the middle, so that the narrative jumps from the early chapters to a much later part. The research, he said, suggests those pages were not lost by chance. Flament added that what is missing can sometimes tell us more about Earth's story than what can be seen.
The findings give geologists a tested account of a puzzle that has stood since the 1870s, and may guide how they interpret the rock record from here.
Citações Notáveis
Imagine a book where a huge section in the middle has been ripped out.— Santosh Dhungana, University of Wollongong
A single, long period of uplift followed by a long period of sinking would have been the ideal recipe for removing the rock and preserving the worn surface.— Assoc Prof Nicolas Flament, University of Wollongong
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