How quickly are the continents moving apart? Our continents are moving apart at a rate of 2.5 cm every year.
The surface of Earth is divided up into 15 tectonic plates. There are seven major plates and eight minor ones. The major plates are named after the continents that are on them: African, Antarctic, Eurasian, Indo-Australian, North American, Pacific, and South American. The largest plate is the Pacific plate. These plates are constantly moving. They sit on the Earth’s mantle, which is a 3000 km thick layer of solid rock that is weak and ductile. This weak rock is heated by radiation from the outer and inner core to the point where it becomes plastic and able to move, despite still being solid. The heat from the Earth’s core produces convection currents that move the plastic rock in different directions. These convection currents move the tectonic plates with them.
The tectonic plates move in many directions, and they come up against each other. When an ocean plate meets a continental plate, the softer ocean plate is forced under the harder continental plate. This is called a convergent boundary. If two hard continental plates collide, neither will sink under the other and they will crumple up to create mountain ranges. If two plates are moving away from each other, they create a divergent boundary. The gap is filled by rock rising from inside the mantle. If two plates are moving past each other, it is called a transform boundary and the tension they produce can cause earthquakes.
So, how quickly are the continents moving apart? Well, they are not all moving apart. Some of them are moving towards each other. The plates travel at different speeds with the slowest being about 1.5 cm a year and the fastest about 5 cm a year. There have been several supercontinents since the Earth was formed and there will probably be another one in about 300 million years. The continents are always moving and they will keep moving until the sun becomes a red dwarf.
Continental drift, now known as plate tectonics, is taught in schools as accepted theory, but it wasn’t always like that. The theory that continents move was first put forward by Abraham Ortelius in 1596. He looked at maps (not as accurate as modern maps by any means – in fact, Australia and large parts of America had yet to be discovered) and realized that continents on both sides of the Atlantic Ocean looked like they fit together. From the late 1800s up until World War 2, there were several theories that continents moved, but nobody could explain why, and there was a lot of opposition to the idea. People could see that the continents appeared to fit together, and similar dinosaur fossils had been found on different continents, but people couldn’t see how something as heavy as a continent could move. Other ideas, such as land bridges that have sunk, were put forward to explain the fossils.
In 1920, a geologist, Arthur Holmes, suggested that the continents sat on plates that were connected under the sea. He also suggested that heat from the Earth’s core created convection currents that moved these plates. He suggested that there must be ridges under the sea that were caused by the plates moving apart. In 1947, these mid-oceanic ridges were discovered, but many people still didn’t believe it.
In 1959, Oceanographers using World War 2 submarine detection technology were able to prove the tectonic plate theory. They used the submarine detection technology to detect magnetic fields on the bottom of the sea. As they pulled the detector across the ocean floor, they found magnetic stripes, but the magnetic poles of these stripes weren’t the same. The magnetic poles alternated. Some had north pointing up and some had south pointing up. How did this prove the tectonic plate theory? Geologists knew that the Earth’s magnetic field occasionally reverses. In the last 83 million years, it has reversed 183 times. When two plates move apart, rock slowly rises from the mantle and hardens in the gaps, becoming new sea floor. The alternating magnetic stripes are caused because the magma pushed out at different times during Earth’s history, proving that the new crust is constantly being formed, and always has been. Nobody could argue against this, and the idea of plate tectonics was accepted. I wonder what the continents will look like in the future. And that is what I learned today.
Sources
https://en.wikipedia.org/wiki/Seafloor_spreading
https://en.wikipedia.org/wiki/Mid-ocean_ridge
https://en.wikipedia.org/wiki/Supercontinent
https://www.amnh.org/explore/ology/earth/power-of-plate-tectonics/mountains
https://www.scientificamerican.com/article/what-do-we-know-about-the/
https://education.nationalgeographic.org/resource/continental-drift
https://oceanservice.noaa.gov/facts/tectonics.html
https://www.earthquakeauthority.com/Blog/2020/Understanding-Plate-Tectonic-Theory