Alfred Wegener figured out that the continents were once all joined together in a single supercontinent, which he named Pangaea, and have been slowly drifting apart for millions of years. This theory is known as Continental Drift.

Here's what he observed that led him to this conclusion:

* Matching coastlines: The shapes of the continents, particularly South America and Africa, fit together like puzzle pieces.

* Fossil evidence: Identical fossils of plants and animals were found on continents now separated by vast oceans, suggesting they were once connected.

* Geological evidence: Similar rock formations and mountain ranges could be found on continents now far apart, indicating they were once connected.

* Climate evidence: Evidence of glacial deposits in tropical regions suggested that the continents had once been located in different positions.

However, Wegener's theory was initially met with skepticism because he couldn't provide a convincing explanation for *how* the continents moved. It wasn't until the development of plate tectonics in the 1960s, which explained the movement of the Earth's crust, that Wegener's theory was finally accepted.

Wegener's work was a major breakthrough in our understanding of the Earth's history and how it continues to change.