About what percentage of the Earth's surface is covered by water?

Water covers about 71 percent of the Earth's surface, mostly as oceans and seas. Land makes up only about 29 percent. That is why the Earth is often called the "Blue Planet" or the "Water Planet".

Area figures:

• Total surface area of the Earth: about 510 million square km.
• Water area: about 361 million square km.
• Land area: about 149 million square km.

Distribution between the hemispheres:

The Northern Hemisphere has much more land than the Southern Hemisphere. About 39 percent of the Northern Hemisphere is land, compared with about 19 percent of the Southern Hemisphere.

So, the Northern Hemisphere is sometimes called the "Land Hemisphere" and the Southern Hemisphere the "Water Hemisphere".

If the Earth is divided so that one half contains the most land possible, that "land hemisphere" is centred near western France, and the opposite "water hemisphere" is centred near New Zealand.

The five oceans by area:

• Pacific Ocean: about 46 percent of the world ocean; larger than all the land on Earth combined.
• Atlantic Ocean: about 23 percent.
• Indian Ocean: about 20 percent.
• Southern Ocean: about 6 percent.
• Arctic Ocean: about 4 percent.

Average depth:

The average depth of the oceans is about 3,700 metres.

Importance of the oceans:

• They regulate the Earth's climate by absorbing and distributing heat.
• They absorb large amounts of carbon dioxide.
• They provide food, minerals, energy and transport routes, and support a vast variety of life.
• Most of the oxygen we breathe comes from tiny marine plants called phytoplankton, along with land plants.

Water on other planets:

The Earth is the only known planet with large bodies of liquid water on its surface, although water ice exists on Mars and liquid oceans may exist beneath the icy crusts of some moons, such as Europa and Enceladus.

Why not the other options?

• ✗About 50 percent and about 85 percent are incorrect.
• ✗About 29 percent is the share of land, not water.