Friday Headlines, September 19, 2014
THE LATEST IN THE GEOSCIENCES
An aquatic dinosaur!
Eruptions in the Philippines
What started plate tectonics?
Spinosaurus is an interesting sail-backed dinosaur. It was featured as the villain-osaur in the third movie in the Jurassic Park franchise. I has the curious look of being a cross between a crocodile and some manner of bird, leading some to refer to it as a ‘crocoduck.’ Of course, it is neither of those things.
In the Jurassic Park movies, Spinosaurus is depicted as a terrestrial carnivore. It ultimately gets in a big fight with a T. rex.
New research shows that this massive carnivore was an active swimmer.
It’s the first documented swimming dinosaur!
Before you say it… No, mosasaurs, plesiosaurs, pliosaurs, and ichthyosaurs are not dinosaurs. Neither are phytosaurs or champsosaurs. They are swimming reptiles, but they are not dinosaurs.
Until this discovery, a person (like me) would adamantly define dinosaurs as terrestrial organisms. If it flew or if it swam, it could not be a dinosaur.
Now, I have to go change all my lecture notes.
Another volcano is blowing its top in the Philippines. This time it’s Mount Mayon, put there are several volcanoes in the island country.
Earthquakes and volcanoes are common in the Philippine Islands due to their tectonic setting. These islands lie within what is called the “Ring of Fire” along the margin of the Pacific Ocean. The Ring of Fire gets its name from all the volcanoes that dot the edge of the ocean. These volcanoes (and earthquakes too) are due to the subduction of the Pacific ocean floor under the continents. Another way to think of it is that the continents are over-riding the Pacific Ocean.
You can learn more about the process of subduction here.
The Philippines are bounded on both the east and west sides by subduction zones, shown by dark lines with teeth on them (the little triangles) on the map below. The teeth are always on the over-riding plate. You can see that the Philippines are over-riding oceanic crust from both sides, which makes for a very complex tectonic situation.
The map above shows historical earthquake activity within and around the Philippines. The different colored circles show earthquakes that have happened since 1900.
The Earth’s continents are in motion. Oceans are getting broader in some places, while in other, the sea floor is being gobbled up underneath mountain ranges.
This process, called plate tectonics, has been happening on Earth for the last 3 billion years of the planet’s 4.6 billion year history. I’ve written a bit about plate tectonics in this post here.
The question is, how did it start?
A paper published this week in Nature has proposed an answer. It’s related to how tectonic plates move in the first place.
An early model to explain plate tectonics was convection, wherein the rock of the Earth’s mantle flowed up in certain places and down in others, much like water in a pot when it’s boiling. The hottest parts of the mantle flow upwards toward the surface while cooler parts flow downward. These zones of up and down flow are connected by areas of horizontal flow. Crust on the surface is dragged along by this flow and may be drawn down where the mantle flows down.
It’s more complex than that, however. And it’s possible that the convection began after plate tectonics began because of plate tectonics.
Where there is up-flow in rocks in the mantle, there is often volcanoes on the Earth’s surface. The rising mantle rocks bring up heat and molten rock forms near the surface. Volcanoes erupt, adding more rocks to the crust.
It’s all this new rock on the Earth’s surface that is now believed to have started plate tectonics. The sheer volume and weight of the new rock caused it to push outward from the volcanoes that formed it. This pushing caused the crust on each side of the volcano (or line of volcanoes) to move in opposite directions away from the volcanoes. This process is called “Ridge Push.”
The Earth is a finite size, so if on one side there is expansion or spreading a crust on opposite sides of a volcanic chain, somewhere else, crust must be consumed or drawn back into the Earth in a process called subduction.
The new model shows that ridge push was the necessary process that started plate tectonics. Subduction was triggered because the crustal material had to go somewhere. The Earth could not get larger to accommodate more crust, so subduction and plate tectonics were a natural consequence.