Nancy Lowe, age 10, of Lowell, Mass., for her question:

WHAT IS TUNDRA?

Tundra is the name of the low, swampy plains which lie around the Arctic ocean in northern Europe, Siberia and North America, and in a few areas of the Southern Hemisphere.

The name "tundra" is also given to the dense growth of peat moss which covers the land. Some scattered shrubs which blossom in early autumn also grow on the tundra.

The ground is perpetually frozen to a great depth, except for a shallow surface layer that thaws in summer. This ground is called permafrost.

Prehistoric animals have been found pr •sprved in the Arctic's tundra and permafrost.

Permafrost, the permanently frozen layer that is made up of rock, sand and soil, actually covers about a fourth of the world's land. Some permafrost is always covered with ice and snow. In some places, the ground is frozen to depths up to 3,000 feet.

Permafrost may thaw from the heat present in buildings and other structures.