The oceans cover about two-thirds of the Earth’s surface and have existed for more than 3,000 million years!
The top layer of the ocean has a rich plant and animal life, the ‘plankton’. Millions of these minute organisms produce food for all the other sea animals. Plankton is one of the oldest forms of life on Earth. Deeper down at about a hundred metres, it is too dark for plants to grow, so the ocean bottom is mostly bare.
Winds blowing across the ocean cause waves. When winds blow over a great distance across the sea, they build waves which may be many metres tall.
The tides
Tides are caused by the pull of the Moon and the Sun on the waters of the Earth. When both the Sun and the Moon are in line with the Earth, their pulls add up, and the tides are very large. These are called ‘spring tides’. When the Sun and Moon are out of line with the Earth, their pulls oppose each other, and the tides are not so large. These are called ‘neap tides’.
Cannon Beach, Oregon, USA. The action of the waves can cause erosion of the coastline.
Papua New Guinea islands, Pacific Ocean – the seas make up two thirds of the Earth’s surface.