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The Earth is the only planet in our solar system known to have life. It is the third planet from the Sun and has one moon. Scientists believe the Earth formed about 4.5 billion years ago. During the Earth’s early development, a large object collided with it causing debris to explode into space. This debris eventually formed the Moon.

The Earth has three layers. The nickel-iron core has a strong magnetic field. A mostly solid mantle of pyroxene, olivine, and garnet encloses the core. The final layer, the crust, is the thin covering over the mantle. It is composed of plates that are constantly moving. This shifting is responsible for many of Earth’s landforms, such as mountains, valleys, deep-sea trenches, and volcanoes. Wind, water, and glaciers continue to erode the surface and contribute to landform creation.

The Earth’s atmosphere is composed of nitrogen (78%) and oxygen (21%). A mixture of other gases comprise the remaining 1%. Part of the oxygen in the atmosphere is in the form of ozone which protects us from the Sun’s harmful ultraviolet rays.

Water is plentiful on Earth. It occurs in the atmosphere as vapor and as a solid and a liquid on the planet surface. Seventy per cent of the surface is covered by water. Most of this water is salt water found in the oceans. Only 2% of the Earth’s water is fresh water (salt free). Most of that supply, 80%, is frozen in glaciers located at the poles.

The Earth’s temperature is moderate compared to the rest of the solar system. This temperature stability allows an abundance of life. Most of the Sun’s energy falls around the equator. Ocean and air currents, however, distribute this heat over the planet.

The Earth’s diameter is 7,928 miles (12,756 km), just a few hundred miles larger than Venus. The Earth circles the Sun every 365 days. A day on Earth is 23 hours and 56 minutes long. The four seasons are the result of the Earth rotating at a 23 degree tilt. For example, during the summer season in the northern hemisphere, that area receives more light and heat because it is tipped toward the Sun. The Sun’s rays hit the surface more directly during this time. As the Earth orbits, the part of the Earth that faces the Sun more directly changes four times resulting in the four seasons.

The abundance of water, oxygen, and stable temperatures provides a good environment for life. In recent years, many people have expressed concerns about air and water pollution. The increase in the amount of carbon dioxide in our atmosphere has created a "greenhouse effect". A layer of carbon dioxide traps the Sun’s heat and prevents it from flowing back into space. Scientists have expressed concern about the long-term temperature implications. In addition, water pollution has threatened the purity of many countries’ water supplies. Maintaining the planet as a healthy environment for all people has become a very pressing concern.

Earth Facts

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