Earth > What Do You Know About Earth?

ANSWER: underwater

About 90 percent of all the volcanoes that erupt on Earth each year occur at the bottom of the ocean where plates are spreading apart. Magma from Earth's upper mantle rises up to fill the cracks that occur when plates separate. While these volcanoes don't explode like some volcanoes on land, they are constantly erupting.

ANSWER: volcanoes and earthquakes

Volcanic eruptions and earthquakes tend to occur along plate boundaries. Volcanoes form and erupt when one plate subducts, or sinks below another, or where plates are spreading apart. Earthquakes occur along all types of plate boundaries — anytime plates grind together and pressure builds up.

ANSWER: both A and B

Rocks hold important clues about our planet. They can tell us about remote places that we can't go to and about distant times in the past. Scientists study rocks to learn about the history of Earth.

ANSWER: by anyone

Rocks can be collected by anyone. You don't need to be an expert. Remember to always have an adult with you and don't go on private property.

ANSWER: sedimentary

Sedimentary rocks are mostly formed from layers of sand, silt, dead plants, and animal skeletons. These rocks are like time capsules. They can show you what life was like at different times. Generally, as you dig deeper into sedimentary rocks, you are going back in time.

ANSWER: a chain of over 500 active volcanoes

The Pacific Plate is subducting under several other plates. This movement forms a long chain of volcanoes called the Ring of Fire . It stretches from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the western coast of North and South America. These are some of the most explosive volcanoes in the world.