EARTH

Pretend you are an alien explorer from outer space looking for life on other planets. Your spaceship flies into a group of stars that looks like a gigantic whirlpool. The whirlpool is the Milky Way Galaxy.

You head for a star with nine planets in one arm of the Milky Way. The third planet from the star is a beautiful blue, white, and green ball. This planet looks like it has life. The name of this planet is Earth.

HOW DOES EARTH MOVE IN SPACE?

Earth spins like a top on its axis. Earth’s axis is an imaginary line that goes through Earth from the North Pole to the South Pole. Earth’s axis is slightly tipped, like a spinning top leaning to one side.

Earth travels around the Sun at about 67,000 miles per hour (about 107,000 kilometers per hour). One year is one trip around the Sun. Earth’s path around the Sun is slightly oval-shaped. This oval shape causes Earth’s distance from the Sun to change during the year.

WHAT MAKES DAY AND NIGHT?

The Sun seems to rise in the morning, cross the sky during the day, and set at night. However, the Sun does not actually move around Earth. Earth’s turning on its axis makes it look as if the Sun is moving.

Earth makes a complete turn on its axis every 24 hours. As Earth turns, half of the planet faces the Sun, and the other half faces away. It is daytime on the half facing the Sun. It is night on the half facing away from the Sun.

WHY ARE THERE SEASONS?

Earth has seasons because of the tilt of its axis. For part of the year, the top half of Earth is tipped toward the Sun. The top half of Earth is called the Northern Hemisphere. During another part of the year, the bottom half of Earth is tipped toward the Sun. The bottom half is called the Southern Hemisphere. It is summer in the half that is tipped toward the Sun. It is winter in the half tipped away. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere. During spring and fall the hemispheres are tipped neither toward nor away from the Sun.

The equator is an imaginary line around Earth’s middle. The farther you are from the equator, the greater the difference in temperature between seasons. The equator never tips far from the Sun. Near the equator it is warm enough to go swimming all year long. The average temperature barely changes from month to month. In Alaska, far from the equator, the average temperature in January can be more than 60 degrees colder than it is in July.

WHY IS THERE LIFE ON EARTH?

Earth has just the right conditions for life. It is not too hot or too cold. Earth has lots of liquid water and an atmosphere (gases) that can support life.

The first kinds of life may have appeared on Earth 3.8 billion (3,800,000,000) years ago. Several times during Earth’s history, almost all life went extinct, or disappeared. Each time, some life forms survived. The survivors spread all over the planet. Dinosaurs appeared about 230 million years ago. Dinosaurs went extinct about 65 million years ago. Scientists believe that modern humans appeared about 130,000 years ago.

WHAT IS THE INSIDE OF EARTH LIKE?

Earth is made of layers. The top layer is called the crust. It is made of hard rock and soil.

More than 70 percent of Earth’s crust is covered with water. Most of the water is salt water in the ocean. Pieces of dry land called continents rise above the ocean. The part of Earth’s crust under the ocean is called the seafloor.

Under the crust is a layer of partly melted rock called the mantle. Under the mantle is Earth’s core. The core is mostly iron. The outer part of the core is liquid metal. The inside of the core is solid metal. Scientists believe that the liquid metal makes Earth a giant magnet and creates Earth’s magnetic field.

Earth’s crust is made of gigantic slabs of rock called plates that move over the mantle. Plates crash together to make mountains. They pull apart and let red-hot rock ooze up from inside Earth to make new crust.

HOW DID EARTH FORM?

Scientists think that Earth and the rest of the solar system formed from a spinning cloud of gas and dust. Gravity pulled most of the gas and dust together to form the Sun. Some leftover gas and dust formed Earth and the other planets. Scientists think that Earth and the Moon formed about 4.6 billion years ago.

Global warminggggg !!!!

Global Warming

Do you like warm weather? Do you wish it could be warmer still? Be careful what you wish for. The Earth may be moving in that direction. The trend is called global warming.

Not all scientists agree that global warming is happening. Some say it is impossible to know if the climate is changing overall. After all, temperatures vary from day to day and year to year. Most scientists, however, say the trend is up. The warmest days are warmer, the coldest days not as cold. They point out that the ten warmest years of the last century happened after 1980. The three hottest came after 1990. The hottest year on record was 1998.

These scientists say the Earth has warmed up about 1° Fahrenheit (0.6° Celsius) in the last 100 years. The rate of change, they say, is speeding up. A hundred years from now, the Earth may well be as much as ten degrees hotter!

WHAT CAUSES GLOBAL WARMING?

Sunlight brings energy to the Earth. This light turns to heat when it hits the ground. The heat in turn seeps away from the Earth, but the atmosphere slows the heat’s escape. The atmosphere is a layer of air around the planet. It holds in some of the warmth.

The atmosphere is a mixture of many gases. In the last 250 years, this mixture has been changing. The amounts of gases such as methane and carbon dioxide have been rising. These gases trap heat more effectively than other gases. They make the Earth’s atmosphere act like the glass in a greenhouse. It lets sunlight in, but it doesn’t let heat out. As a result, heat is building up close to the surface.

WHY IS THE ATMOSPHERE CHANGING?

People are changing the atmosphere. The changes started hundreds of years ago when people began cutting down forests and burning the wood. The invention of cars and other machines greatly increased the amount of greenhouse gases released into the atmosphere. Such machines burn fuels like wood, coal, oil, and natural gas. When these fuels burn, they add carbon dioxide to the atmosphere. Methane comes from producing coal.

Today, the air contains almost one-third more carbon dioxide than it did in 1750. The amount of methane has doubled.

IS GLOBAL WARMING DANGEROUS?

Global warming could melt the ice at the poles. This would raise the level of the oceans. Water would then cover all the flat coastal lands. People would have less land on which to live and grow food.

Plants and animals are adapted to their climates. If the climate changes rapidly, many may not be able to adapt. Some species will simply die out. Others may spread to cooler climates. There, however, they will be struggling with species already in place.

CAN GLOBAL WARMING BE STOPPED?

Burning less wood, coal, oil, and natural gas will help stop global warming. Scientists recommend that people get more energy from sunlight, wind, tides, nuclear energy, and other sources that don’t burn fuel. Energy sources like these put little or no greenhouse gases into the air.

Scientists say trees can help prevent global warming. All growing plants take carbon dioxide out of the air. Trees do this especially well. They turn the carbon part of carbon dioxide into wood. They release the oxygen. In recent years, people have been cutting down forests all over the world. Scientists say vast new forests must be planted.

WHAT IS BEING DONE?

In 1997, officials from 160 countries met in Kyoto, Japan. They wrote an agreement called the Kyoto Protocol. Countries that sign this agreement promise to burn 5 percent less fossil fuel (coal, oil, and natural gas) by 2012. In 2002, however, the United States decided not to sign the treaty. Russia also has not signed the treaty. Without the United States and Russia, the treaty can’t work.