# A Lumpy Planet

So you yearn to explore strange worlds in distant galaxies, going where no Earthling has gone before? And you're feeling very depressed that for technical reasons your trip might be delayed a few centuries…or maybe forever? Well, how about visiting the world in this photo? Is it weird enough for you?

Gravity map Courtesy NASA

Surprise! It's Earth. But not as we normally see it. This image shows Earth as it is seen by instruments that are sensitive to gravity instead of light. Gravity isn't the same all over the planet. The mappers turned places where you'd feel slightly heavier into high spots and ones where you'd feel slightly lighter into lows. One of the lows is in India (the blue and pink area to the right of center). You'd weigh about a pound less if you went to India (if you weighed about 100 pounds normally).

Scientists think the gravity map reveals what's going on deep inside Earth, in the part called the mantle, where the rock is still solid but hot enough that it flows slowly. That low off of India may be linked to an ancient collision—the collision of India with Eurasia, which pushed up those wrinkles on the surface of Earth we call the Himalayas.

It just goes to show: There's no place like (or as weird as) home!

## Vocabulary

• gravity: Pulling forces between objects.

Back to Top

## Activity

1. This map shows that there are minor variations in gravity around the surface of the planet. The variations may mean that in some places the same object would weigh slightly more than it would in other places, depending on the pull of gravity in each place. What if gravity varied greatly over the surface of the Earth? What if something that weighed 100 pounds on land weighed only 50 pounds in the water? Imagine that the pull of gravity varied greatly over the Earth's surface. What would the effect be on life on land and life in the ocean? What would the effect be on how the surface of the Earth changed over time? Write a paragraph describing how life would vary.