Plate Tectonics

Plate Tectonics Theory is the theory that Earth’s lithosphere is divided into separate plates that float independently over the asthenosphere (lower mantle). This mechanism is what explains the movement of landmasses over time and space.

Earth’s crust is broken into several major and minor pieces called ‘plates’. The convection of the asthenosphere, driven by uneven heating through the decay of unstable radioactive elements, drives the movement of these plates.

Imagine that you have an Oreo cookie – or actually get one! Twist off the top, trying to keep it in one piece, and don’t eat it. Picture the cream layer as the asthenosphere, and the cookie you twisted off is the lithosphere. Set the cookie back on the cream filling: this is the crust and upper mantle ‘floating’ over the taffy-like lower mantle.

What we today call plate tectonics used to be called the theory of continental drift. In 1912, a German geophysicist named Alfred Wegener paired rock assemblages and coal deposits that today are on different continents, but geologically appeared to be the same formations. He used this evidence to propose the theory of continental drift. At the time, this theory was hugely controversial – it was not more widely accepted until new scientific methods emerged in the 1950s-60s which helped verify it.

Paleogeologists use fossil records to reconstruct ancient continents by examining how fossilized organisms are distributed across Earth's surface.

Alfred Wegener was the first to identify earlier configurations of Earth’s continents, and is credited with identifying the prehistoric supercontinent Pangea. Earth’s continents have existed in drastically different positions than they are presently. Since then, many other continental configurations have been identified/hypothesized:

• Pangea (225 million years ago)
• Rodinia (75-1.1 billion years ago)
• Columbia (1.8-2.0 billion years ago)
• Kenorland (2.7 billion years ago)
• Vaalbara (3.1 billion years ago)

Kenorland is a supercontinent theorized to have existed about 2.7 billion years ago. This illustration is a reconstruction from plate tectonics researchers in a 2020 paper (Slabunov et al. 2020 Links to an external site.).

You can check out some of Earth's earlier continental positions with this interactive globe Links to an external site.! You can also watch this animation Links to an external site. of how the continents have shifted to form some of the configurations above.