Tectonics Practice Quiz 1 on QuizRevolution

The Asthenosphere is the layer of the mantle that the Lithosphere (tectonics plates) floats upon. It is solid, but plastic. Convection currents in the Asthenosphere move the tectonic plates.

The San Andreas Fault is where the Pascific Plate is moving north and the North American Plate is moving south. The plates are moving past each other, rather than colliding or diverging.

Before we came up with the Theory of Plate Tectonics and before we discovered that the seafloor is spreading out from mid-ocean ridges, we noticed that there was evidence that continents have moved around the Earth. This original idea is called Continental Drift because it suggests the continents have "drifted" around.

The North American, African and Indo-Australian plates are all continental plates. Continents are not dense enough to sink into the mantle and subduct. The Nazca Plate is an oceanic plate, and is denser. Only oceanic plates can subduct.

Glacial deposits from the late Paleozoic Era have been found in Africa, India, Australia, South America, and Antarctica. Glacial striations (scratches) on rocks in all these continents show the directions all the glaciers were moving. All of them were spreading out from a central area somewhere in southeastern Africa. That means the south pole was probably once in that part of Africa.

The Earth's magnetic field switches directions from time to time. That means that that a compass would point south instead of north. The seafloor preserves a record of these magnetic reversals because when lava cools, it freezes magnetic crystals in place, showing the direction of the magnetic north pole. There is a matching record of magnetic reversals on each side of the mid-ocean ridges throughout the world's oceans and it shows that ocean floors have been spreading out from mid-ocean ridges where new oceanic crust is being created.

Divergent because it is where two oceanic plates are spreading apart. Divergent boundaries are constructive, meaning they create new crust. It is not convergent because that means moving together and it is not transform because that means moving past each other, side-by-side. Lithosphere is what the plates are made of and is not a type of boundary.

The answer is the theory of plate tectonics. Continental drift and seafloor spreading were earlier theories that did not include the idea of plates and did not include the idea of the plates floating on the asthenosphere. Subduction just describes a process of one plate sliding under another.

Transform boundaries are neither convergent nor divergent. They are simply where plates slide past each other, side-by-side. Subduction zones form at convergent boundaries that have at least one oceanic plate. Mid-ocean ridges are divergent boundaries in the ocean.

Convergent oceanic-oceanic boundaries produce volcanic island chains (also called volcanic island arcs). Folded mountains are made by convergent continental-continental boundaries. Strike-slip faults can form along many types of boundaries, but mainly form at transform boundaries. Mid-ocean ridges form at divergent oceani-oceanic boundaries.