Deep in the canyon walls of Arizona, the Earth keeps a silence: younger sediment lying directly on rock that is perhaps two billion years old, with an entire chapter of geological time simply absent. For roughly a century and a half, scientists have stared at that missing span and wondered what erased it. Now a team in Australia, working through computer simulations of the planet's slow internal churning, proposes that the vanished layers were not lost by accident but were worn away when ancient continental cores rose and then sank, burying their scarred surfaces beneath the sea. It is an offe
Sinking continents may explain Earth's missing rock record, a 150-year-old geological gap
Sometimes what is missing can tell us more about the story of Earth
Mark
So what exactly is the Great Unconformity?
Mimi
A gap. In places around the world, Cambrian rock, about 540 million years old or younger, sits directly on basement rock that can be over a billion years old. The Grand Canyon shows it starkly.
Mark
And the new idea is what, in plain terms?
Mimi
That ancient continental cores, including those of North America, northern Europe and northern China, rose in the Neoproterozoic and then sank over the last 540 million years. The rising let erosion strip rock away, and the sinking buried the worn surface.
Mark
Why has this been so hard to settle?
Mimi
Because the evidence is what's missing. You can't examine rock that isn't there, so ideas are hard to test.
Luke
I'd flag that this is a simulation. The Nature paper reports what the model shows, but a model producing uplift then subsidence isn't the same as directly observing it.
Mark
Fair. Is the computing effort meaningful?
Mimi
It's substantial. Each run took around 75,000 CPU hours on Gadi.
Luke
Effort isn't validation, though. The reporting says conclusions still need checking against other geological evidence, and it doesn't say how that has gone so far.
Mark
Does it claim to explain every instance of the gap?
Luke
The coverage only names three regions in the model. Whether it accounts for unconformities elsewhere isn't stated, so I wouldn't assume it.
Mimi
Flament's own framing is careful: he says it proposes a solution. That's the honest register.
O Pulso
- A gap in the rock record, first noticed in the 1870s, has refused to yield its secret for a century and a half.
- Researchers at the University of Wollongong ran mantle convection models on Gadi, consuming around 75,000 CPU hours per simulation.
- The models show ancient continental cores rising through the Neoproterozoic, then slowly sinking through the Phanerozoic, scouring and then burying the land.
- The idea is promising but unproven, and its next trial is whether the predicted uplift and subsidence match what the rocks actually record.
Deep in the canyon walls of Arizona, the Earth keeps a silence: younger sediment lying directly on rock that is perhaps two billion years old, with an entire chapter of geological time simply absent. For roughly a century and a half, scientists have stared at that missing span and wondered what erased it. Now a team in Australia, working through computer simulations of the planet's slow internal churning, proposes that the vanished layers were not lost by accident but were worn away when ancient continental cores rose and then sank, burying their scarred surfaces beneath the sea. It is an offering rather than a final answer, a story that must still be tested against the rock itself.
In the walls of the Grand Canyon, a strange contact can be seen by anyone who looks closely. Sedimentary rock about 540 million years old rests directly on basement rock that may be two billion years old, and whatever should lie between them is missing. Geologists call this absence the Great Unconformity, and it has puzzled them since it was first identified in the 1870s.
The difficulty has always been that the evidence is a gap. Many explanations have been offered over the decades, but few have been checked against how the Earth actually behaved over time, and an absence is hard to test. Researchers at the University of Wollongong describe the problem as a book with a large section torn out, the story leaping from early chapters to a much later one.
Associate Professor Nicolas Flament and PhD candidate Santosh Dhungana turned to Gadi, one of Australia's most powerful supercomputers, to run mantle convection simulations. Their models showed the ancient cores of North America, northern Europe and northern China rising during the Neoproterozoic, then subsiding over the past 540 million years. As those cores sank beneath the ocean, their eroded surfaces were buried, and the missing pages were sealed away.
Flament called the result a thrill, noting that sometimes what is missing tells us more about Earth's story than what we can see. The work, published in Nature, is still a proposal. Its conclusions must now be weighed against other geological evidence, and the real test is whether the pattern it describes can be found in the rock record itself.
In the walls of the Grand Canyon in Arizona, a strange contact is visible to anyone who looks closely. Sedimentary rock about 540 million years old, or younger, rests directly on ancient basement rock that may be up to two billion years old. Whatever should lie between them is not there. Geologists call this gap the Great Unconformity, and a team at the University of Wollongong now says it has a model that explains how it formed.
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, the time of the explosion of animal life some 540 million years ago, sit straight on top of rocks that can be more than a billion years old. The feature was first identified in the 1870s, and the puzzle has stood for roughly 150 years.
Part of the difficulty is that the evidence is an absence. Many researchers have proposed explanations over the decades, but testing them has been hard, because the thing being studied is what is missing. Associate Professor Nicolas Flament said few of the proposals had been checked against how the Earth actually behaved over time.
His colleague, PhD candidate Santosh Dhungana, described the problem as a book with a huge section torn out of the middle, the narrative leaping from early chapters to a much later part. The research, he said, suggests those pages were not lost by chance.
Dhungana and Flament ran mantle convection models on Gadi, one of Australia's most powerful supercomputers. Each simulation took about 75,000 CPU hours to complete. The models showed the ancient cores of North America, known as Laurentia, and of northern Europe, known as Baltica, along with northern China, rising during the Neoproterozoic Era, between one billion and 540 million years ago. They then subsided during the Phanerozoic eon, which covers the past 540 million years.
As those continental cores sank into the ocean, the worn rock surface was buried, forming the Great Unconformity, according to the research published in the journal Nature. Flament said a single long period of uplift followed by a long period of sinking would have been the ideal recipe for removing the rock and then preserving the eroded surface.
"Sometimes what is missing can tell us more about the story of Earth than what we can see," Flament said, adding that it was a thrill to propose a solution to the puzzle.
The work is a model-based proposal rather than a final verdict. Its conclusions will need to be validated against other geological evidence, and the next test is whether the pattern of uplift and subsidence it describes holds up against the rock record itself.
Citações Notáveis
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
Our research suggests these pages weren't lost by chance.— Santosh Dhungana, University of Wollongong
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