Ocean Unit Introduction

Ocean Unit Introduction

Introduction

Much of Earth’s surface is covered with oceans. That’s why Earth is called the “water planet.” Without all that water, Earth would be a very different place. The oceans affect Earth’s atmosphere and influence its climate. An incredible diversity of living things inhabit the ocean as well. You might think that oceans have always covered Earth’s surface, but you would be wrong!

Multiple Choice

How did comets help form oceans?

• comets are made of rock

• comets are made of salt

• comets formed fish

• comets are made of ice

How the Oceans Formed

When Earth formed 4.6 billion years ago, it would not have been called the “water planet.” There were no oceans then. In fact, there was no liquid water at all. Early Earth was too hot for liquid water to exist. Earth's early years were spent as molten rock and metal.

Multiple Choice

True or False?

Early Earth was too cold for liquid water to exist.

• True

• False

Water on Early Earth

Over time, Earth cooled. The surface hardened to become solid rock. Volcanic eruptions, like the one in the image, brought lava and gases to the surface. One of the gases was water vapor. More water vapor came from asteroids and comets that crashed into Earth. As Earth cooled still more, the water vapor condensed to make Earth’s first liquid water. At last, the oceans could start to form.

Multiple Choice

Sources of water vapor in Earth’s very early atmosphere included

• volcanic eruptions

• the moon

• precipitation

• the oceans

Ancient Oceans

Earth’s crust consists of many tectonic plates that move over time. Due to plate tectonics, the continents changed their shapes and positions during Earth history. As the continents changed, so did the oceans. About 250 million years ago, there was one huge land mass known as Pangaea. There was also one huge ocean called Panthalassa. You can see it on the picture on the next page.

Ancient Oceans Continued

By 180 million years ago, Pangaea began to break up. The continents started to drift apart. They slowly moved to where they are today. The movement of the continents caused Panthalassa to break into smaller oceans. These oceans are now known as the Pacific, Atlantic, Indian, and Arctic Oceans. The waters of all the oceans are connected. That’s why some people refer to the oceans together as the “World Ocean.”

The Oceans’ Influence

Oceans cover more than 70 percent of Earth's surface and hold 97 percent of its surface water. It’s no surprise that the oceans have a big influence on the planet. The oceans affect the atmosphere, climate, and living things.

Oceans and the Atmosphere

Oceans are the major source of water vapor in the atmosphere. Sunlight heats water near the sea surface, as shown on the image on the next page. As the water warms, some of it evaporates. The water vapor rises into the air, where it may form clouds and precipitation. Precipitation provides the freshwater needed by plants and other living things.

Oceans and Atmosphere Cont.

Ocean water also absorbs gases from the atmosphere. The most important are oxygen and carbon dioxide. Oxygen is needed by living things in the oceans. Much of the carbon dioxide sinks to the bottom of the seas. Carbon dioxide is a major cause of global warming. By absorbing carbon dioxide, the oceans help control global warming.

Oceans and Climate

Coastal areas have a milder climate than inland areas. They are warmer in the winter and cooler in the summer. That’s because land near an ocean is influenced by the temperature of the oceans. The temperature of ocean water is moderate and stable. Why? There are two major reasons:

1. Water is much slower to warm up and cool down than land. As a result, oceans never get as hot or as cold as land. Water flows through all the world’s oceans.

2. Warm water from the equator mixes with cold water from the poles. The mixing of warm and cold water makes the water temperature moderate.

Multiple Choice

Ocean water everywhere has a relatively moderate temperature because

• water flows throughout all the world’s oceans.

• water warms up and cools down more quickly than land.

• landmasses protect the oceans from temperature changes.

• all of the above.

Oceans and Climate Continued

Even inland temperatures are milder because of oceans. Without oceans, there would be much bigger temperature swings all over Earth. Temperatures might plunge hundreds of degrees below freezing in the winter. In the summer, lakes and seas might boil! Life as we know it could not exist on Earth without the oceans.

Oceans and Living Things

The oceans provide a home to many living things. In fact, a greater number of organisms lives in the oceans than on land. Coral reefs, like the one in the picture, have more diversity of life forms than almost anywhere else on Earth.

Multiple Choice

True or False?

The oceans influence Earth’s atmosphere.

• True

• False

Multiple Choice

True or False?

Fewer organisms live in the oceans than on the land.

• True

• False

Multiple Choice

True or False?

Coastal areas always have colder climates than inland areas.

• True

• False