Note: Continental crust is a lot like pie crust, an ancient frangible confection that inexorably disintegrates!
At least, that’s the case in my kitchen. Although I love to bake, the creation of a flaky, delicate pie crust has eluded me, in spite of my sister-in-law Eileen’s expert tutelage.
If you too have problems with your pie crust or if you just want a healthier dessert, click here for ugly pie recipe)…rich and crusty scones nestled into a delicious baked fruit compote. Not that you care necessarily, but it’s lightening quick to prepare, low-fat, and scrumptious.
Back to geologic time: some pieces of continental crust got smushed together by plate tectonic motion to make a big BIG big continent, the correct term being ‘Supercontinent.’ Rodinia (meaning ‘homeland’ in Russian) became the current continents of North America, South America, Australia, Antarctica, Asia, Africa. One big land mass.
What happens: land comes together, then breaks apart, then comes together again, and breaks apart again (that seems to be where we are right now).
A question: so, are we in the era of smooshing together again? Imagine if we were one big continent (all of us Rodinians or Pangaeans, rather than Americans or Saudis or Somalis or Swiss). And imagine that the climate got harsh again fast — we’d need to work together to survive, especially all of us homo sapiens (the animal that knows).
Right now, are you pulling apart or coming together?
Pulling apart can be an important developmental phase, especially for kids, and is often called ‘differentiation.’ Coming together is equally important — which could mean unifying the self as well as uniting emotionally, as a couple, as a family, as a community.
Rodinia was a stark and hostile land throughout its history. Much of what would become North America was a vast floodplain, building up thick layers of sand and silt. Life had barely progressed beyond single-celled algae.
The causes of supercontinent assembly and dispersal are thought to be driven by processes in the mantle. Approximately 660 km into the mantle, a discontinuity occurs, affecting the surface crust through processes like plumes and “superplumes”. When a slab of crust that is subducted is denser than the surrounding mantle, it sinks to the discontinuity. Once the slabs build up, they will sink through to the lower mantle in what is known as a “slab avalanche” (Figure 3). This displacement at the discontinuity will cause the lower mantle to compensate and rise elsewhere. The rising mantle can form a plume or superplume
About 300 million years ago we come back to the beginning of the cycle, with land mass getting pushed back together and creating a new SuperContinent, called Pangaea (Greek for “all worlds,” pronounced pan-GEE-ah)
Check out this clever animation of Pangea’s dispersal. [thanks to US Geological Survey]
The assembly of the giant continent Pangaea probably caused large-scale climatic disruption and a collapse of many terrestrial and oceanic ecosystems. In this new setting, much of North America reverted to desert. In part, these changes may have contributed to a great mass extinction that occurred 245 million years ago at the end of the Permian Period. Literally 90 percent of all species of life went extinct. This was the largest extinction event in the history of life on Earth – greater even than the extinction of dinosaurs 65 million years ago.
The ultimate cause of this great extinction remains a subject of considerable debate. A growing number of geochemists and paleontologists suspect the Permian-Triassic extinction followed a major impact by an asteroid that disrupted Earth’s ecosystem 245 million years ago.