A solitary chunk of granite, small enough to heft in one hand, is key evidence that Australia and parts of Antarctica were once attached to North America, a new study suggests.

The Earth's continents are thought to have collided to become supercontinents and broken apart again several times in Earth's 4.5 billion year history. The most recent supercontinent was Pangaea, which began to break apart about 200 million years ago; the landmasses that comprised Pangaea eventually wandered into the current configuration of continents.

Several supercontinents predating Pangaea have been proposed by geologists, including one dubbed Rodinia that existed about 1.1 billion years ago.

For several decades, researchers have theorized that part of the ancient supercontinent Rodinia broke away from what is now the southwestern United States around 800 million to 600 million years ago, eventually drifting southward to become eastern Antarctica and Australia. The idea is known as the southwestern United States to East Antarctica (SWEAT) hypothesis.

But there was little physical evidence that could tie the southernmost continent to the long-disappeared Rodinia. Until scientists stumbled upon this rock, that is.