Identical fossils of the reptile Mesosaurus, which lived 300 million years ago, are found in eastern South America and western Africa and nowhere else in the world. Explain how these fossils provide evidence for the theory of plate tectonics.

Mesosaurus fossils offer an exciting clue to our planet's ancient history. These fascinating remnants belonged to a small, freshwater reptile that lived during the Early Permian period, over 300 million years ago. What's truly intriguing is that these fossils have only been found in eastern South America and western Africa.

Imagine finding puzzle pieces in two separate places that fit together perfectly – that's what Mesosaurus fossils are like. When we understand that Mesosaurus couldn't have swum across the vast ocean that now separates the two continents, it raises the question: how did the fossils end up so far apart? This discovery led scientists to a groundbreaking theory that forever changed our view of Earth's history – the theory of continental drift and plate tectonics.

Our Earth's surface is far from static, and the idea of continental drift explains this dynamism. The concept was first formulated by Alfred Wegener in 1912, who proposed that the continents had once formed a single landmass, called Pangea, before breaking apart and drifting to their current positions.

Using evidence like the jigsaw-like fit of the continental shores, similar rock formations on different continents, and, notably, the distribution of prehistoric fossils, including those of the Mesosaurus, Wegener's theory suggested a world in motion. Despite initial resistance, his idea has since been bolstered by extensive geological research and is now a vital element of the plate tectonics theory.

To truly grasp the scale of the changes to Earth's surfaces, one must understand geological time – a vast temporal canvas that extends beyond human history. Geological time is marked by eons, eras, periods, and epochs, which help scientists categorize Earth's 4.6 billion-year history.

For Mesosaurus, living in the Early Permian period of the Paleozoic era, the world was a very different place. At that time, the supercontinent Pangea was intact. Since then, hundreds of millions of years have passed, allowing the tectonic movements to shape the continents as we see them today – evidence of Mesosaurus on separate continents signifies this immense passage of time.

The theory of plate tectonics provides a framework to understand how the Earth's surface is molded. Tectonic plates, large slabs of Earth's lithosphere, float atop the semi-fluid asthenosphere. As they move and interact, they generate a slow but constant reshaping of Earth's geography.

The movements of these tectonic plates can result in the drifting of continents, creation of mountains, and earthquakes. When applied to Mesosaurus fossils, this concept helps us deduce that South America and Africa were once a single landmass, part of Pangea. Over millions of years, the interplay of tectonic plates has led these landmasses to drift apart, separating the population of Mesosaurus and leaving their fossilized remains as breadcrumbs that tell the story of our planet's dynamic nature.