Q: If we think the continents were, at some point, all connected, how did they separate?

Abbie Stroup

Grade 7

Sennett Middle School

A: "The answer is rooted in the fact that our planet is a living' planet, which is still cooling," said Laurel Goodwin, professor of geology at UW-Madison. She describes the Earth as a series of shells, like a peanut M&M. "The candy shell is the crust, on which we live. The chocolate beneath is the mantle, and the peanut is the core -- just imagine that the outer part of the peanut is molten."

This deep, dark region retains heat from the hot gas and dust that formed the Earth about 4.5 billion years ago.

The middle layer, the mantle, is solid rock, but it is hot enough to flow slowly, like Silly Putty. The movement, called convection, brings hot rock from the lower mantle to the surface. Cooler rock at the top of the mantle sinks.

The overall effect of convection is to create "conveyor belts" that transport the giant plates that form Earth's crust.

"As the continental plates are carried along on this conveyer belt, they may crash together (like they did to create the Himalayas), slide past one another (California), or separate (Baja California)," Goodwin said.

Over hundreds of millions of years, the continents have merged and re-separated in their continual movement around the globe. This movement explains why fossils of tropical animals can be found in Antarctica, she said.

-- Produced in cooperation with University Communications