World Biomes





Earth Facts

Earth is the third planet, and 93,000,000 miles (150,000,000 km.) from the sun. It is estimated to be over 4.5 billion years old.

The planet rotates once every 23 hours, 56 minutes, and 4.09 seconds. It makes one full revolution around the sun every 365 days, 6 hours, 9 minutes, and 9.45 seconds. Earth's axis is tilted at a 23.5° angle.

Earth has a total surface area of 196,800,000 square miles. Approximately 57,300,000 square miles, or 29% of the total surface area is land. Water covers approximately 139,500,000 square miles, or 71% of the total surface area.

The highest temperatures on Earth have reached 136° F (58° C) at Al Asisiyah, Libya. Temperatures of - 128° F (-89° C) have been recorded at Vostok station in Antarctica.

The atmosphere is a thin, gaseous layer of air that envelops the planet. Its inner layer is called the troposphere and reaches only 11 miles above sea level. It contains most of the planet's air, which consists of nitrogen (78%) and oxygen (21%). The stratosphere, or outer layer, stretches 11-30 miles above sea level and contains ozone (O3). Ozone filters out most of the sun's harmful ultraviolet radiation.

More than 99% of earth's atmosphere is less than 50 miles (80 km.) high. However, particles of the atmosphere are found 1,000 miles (1,600 km.) in space above the planet's surface.


Our Sun

Our sun is the source of energy for life. Solar energy drives the climate and weather systems of our planet. The sun is a huge ball of hydrogen (72%) and helium (28%) gases. Tremendous pressure and temperatures in its inner core fuses the hydrogen nuclei and forms helium, releasing enormous amounts of energy.

This energy travels at the speed of light and reaches Earth in slightly more than 8 minutes. Earth receives only about one-billionth of the sun's energy. About 34% of the solar energy reaching the troposphere is reflected back into space by clouds, dust, chemicals. Most of the energy reaches the troposphere as visible light, infrared radiation, and a small amount of ultraviolet radiation that wasn't absorbed by the stratosphere.

This unreflected solar radiation is turned into infrared radiation, or heat. Heat-trapping gasses like water vapor, carbon dioxide, methane, nitrous oxide, and ozone affect the speed at which this radiation is returned to space. Without these gasses, known as the natural greenhouse effect, heat would immediately return to space, making it almost as cold as Mars.


Forming Life on Earth

Scientists have studied fossils and made chemical analysis of rocks to find out how life on Earth evolved to its present system. Several theories have been suggested. It is theorized by some scientists that life developed in two phases over billions of years.

In the first phase explosions of dying stars shattered through our galaxy and created swirling clouds of dust particles and hot gases. These extended trillions of miles across space. As the cloud cooled, bits of matter began to cling to each other. Over 4 billion years ago the cloud had formed into a flattened, slowly rotating disk. Our sun was born in the center of this disk. Farther out on the disk, Earth and the other planets formed as bits of matter were drawn together. Earth started out as a molten mass that did not cool for millions of years. As it cooled it formed a thin, hard crust with no atmosphere or oceans.

Molten rock frequently erupted through the crust. Water vapor was released from the breakdown of rocks during volcanic eruptions. Eventually the crust cooled enough for this vapor to condense and come down as rain to form the oceans that covered most of Earth.

In the second phase scientists have recently hypothesized that bubbles floating on the ancient ocean trapped carbon-containing molecules and the other chemicals necessary for life. These bubbles may have popped and released these chemicals into the atmosphere. Organic compounds formed and dissolved in the early atmosphere, collecting in the shallow waters of the earth. Although no one knows how, the first living cells developed between 3.6 and 3.8 billion years ago. Over time these protocells developed into cells having the properties we describe as life.

These single-celled bacteria multiplied in the warm, shallow waters for billions of years. Here they mutated and developed into a variety of protists, fungi and, about 600 million years ago, plants and animals.

Life could not develop on land since there was no ozone layer to shield early life from damaging ultraviolet radiation. Then about 2.3-2.5 billion years ago photosynthetic bacteria emerged. These cells could remove carbon dioxide (CO2) from the atmosphere and, using sunlight, combine it with water to make carbohydrates. In the process they created oxygen (O2) and released it into the ocean. Some of the oxygen escaped into the atmosphere.

Our atmosphere was created over a span of 2 billion years. Some of the oxygen was converted into ozone (O3), which formed in the lower stratosphere and protected life forms from UV radiation. This allowed green plants to live closer to the surface of the ocean, making it easier for oxygen to escape into the atmosphere. About 400-500 million years ago the first plants began to exist on land. Over the following millions of years a variety of land plants and animals evolved.


Living Earth

Earth is truly a remarkable planet. It is the only planet in our solar system that has the components necessary to support life as we recognize it. The planet is only a tiny part of the universe, but it is the home of human beings and many other organisms. Animals and plants live almost everywhere on the surface of Earth.

These organisms can live on Earth because it has an atmosphere. The atmosphere moderates daytime and nighttime temperature swings. The atmosphere filters radiant energy during the day, preventing the surface from overheating. At night the atmosphere prevents most of the radiant heat from escaping back into space, keeping the surface warm.

Most organisms - both plants and animals - must also have water to live. Earth has plenty. Seventy-one percent of its surface is covered by water.

Living things also need nitrogen, oxygen, and carbon dioxide. Earth's thin layer of atmosphere provides all of these elements.

The atmosphere also screens out lethal levels of the sun's ultraviolet radiation. The atmosphere, however, could not exist if Earth were not at the exact distance it is from the sun.

Our Planet
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