Dear Nora,

I live near a few volcanoes. One of them—Mount St. Helens—is bubbling with molten material that will probably gush out as lava someday.

I asked my friend Johannes Hämmerli about lava. He’s an earth scientist at Washington State University.

He told me Earth is mostly solid.

“The very center of Earth is a solid metal ball,” Hämmerli said. “Outside that ball, there’s a thick shell we think is liquid. And the rest of Earth—if you go through the mantle and crust—is pretty much solid.”

Earth formed when a cloud of dust in space collapsed. The elements inside the cloud squished … » More …