Other explanations included cracking, pulling and stretching of the Earth’s crust, and global sea level decline. However, rifting mainly affects the edges of continents, and a change in sea level should have affected all continents equally. “There is no doubt that there was extensive glaciation. There is no doubt that there were sea level changes over time. The question is, was that enough to solve the mystery of the Great Unconformity?” Flament says.
A fourth idea was that the mantle itself moved the continents up and down, a process called dynamic topography. “It has been proposed but not quantitatively tested,” Flament says. So his team set about it.
Lava lamp planet
From about 100 to 200 kilometers below the Earth’s surface to almost 3,000 kilometers, the Earth’s mantle slowly convects. “An analogy would be a lava lamp, where some things come up and others come down,” explains Flament. “Cold rock sinks and hot rock rises.”
The mantle is solid, yet a piece of rock can slowly migrate from the surface to the depths of the Earth over a period of about 200 million years. This movement tugs at the surface. Where cold seafloor plates sink into the mantle at subduction zones, the ground is pulled downward; Where hot mantle rises, it is pushed upward. However, the amplitude of this up and down movement is still debated. “The short distance is several hundred meters, and what exactly that is still needs to be clarified [precise value] is,” says Flament.
Dhungana and Flament conducted six simulations of mantle convection over a billion-year period based on reconstructions of the movement of tectonic plates over that time. They then grouped regions where the ground was raised and lowered in similar ways to figure out where the unconformity should have formed and where it should persist to this day. However, Flament says the initial configuration of these simulations remains uncertain.
