From Ars Technica · · 1m 20s
Earth's Mantle Created Great Unconformity Gap
Earth's mantle movements may have carved a 200-1 billion year gap in rock records.
In brief
Earth's mantle movements may have carved a 200-1 billion year gap in rock records. Earth's mantle convection created the Great Unconformity by uplifting continents and eroding them with glaciers. Originally reported by Ars Technica.
Great Unconformity Gap
The Great Unconformity is a gap in the geologic record between ancient crystalline rocks and Cambrian sandstones.
“It’s called the Great Unconformity, and it’s a gap in the geologic record”
Mantle Convection Theory
Geoscientist Nicolas Flament and colleague Santosh Dhungana propose mantle convection carved the gap.
“Slow currents of hot rock in Earth’s mantle pushed entire continents up for hundreds of millions of years”
Time Scale of Gap
The gap spans 200 million to over a billion years, with North American sediments between 635 and 482 million years old.
“This gap can be anywhere between 200 million years, which is not that impressive, to more than a billion years”
Glaciation Hypothesis
Snowball Earth glaciation could have eroded rock but the gap isn't global, so it's not the full explanation.
“Ice sheets are very good at grinding, scouring, scraping the surface”
Mantle Uplift Process
Mantle convection moves continents up and down over hundreds of millions of years, creating uplift and erosion.
“Cold rock sinks and hot rock rises”
Simulation Results
Six models show Laurentia rose and fell between 930 and 510 million years ago, creating the Great Unconformity.
“Five of the six models showed this pattern of Laurentia seeing long uplift followed by sinking in the Cambrian”
Glacial Erosion Role
Glaciers ground rock on low slopes, working with gentle uplift to create the gap.
“The uplift could create a tilt for the whole continent, but it’s not great at creating a steep slope”
Regional Differences
North America and Eurasia show one uplift cycle, while South America and Australia show two cycles.
“South America and Australia went through two cycles, forming potentially two unconformities”
Cambrian Connection
Erosion from the Great Unconformity may have fertilized oceans before the Cambrian explosion.
“That’s when life learns to mobilize calcium and create skeletons and shells”
The takeaway
Earth's mantle convection created the Great Unconformity by uplifting continents and eroding them with glaciers.
