Introducing Planet Earth
Blue, beautiful Earth is the planet we call home. Even though there are seven other planets that orbit the Sun, Earth is one-of-a-kind in the solar system. It is the only planet that can support life as we know it.
African Elephants roam through a swamp in Kenya. Life is supported by our lush landscape here on earth.©G. Ellis/GLOBIO.org
To us, Earth is huge. It is 12,756 km in diameter and has a mass of6 sextillion metric tons. But compared to the Sun, it’s tiny. If you think of the Sun as being the size of a bowling ball, Earth would be the size of a peppercorn.
Sun gives life to the earth, supplying it with light. The Earth is 1 millionth the size of the Sun.©NASA and European Space Agency
Earth's Place in Space
The sun sets behind the earth from the International Space Station. When the sun sets, that portion of the earth becomes dark and night falls.©NASA
Our planet, along with the entiresolar system, is part of the Milky Way galaxy. This is a vast collection of stars, planets, dust, and gas. Earth is about two-thirds of the way from the center on one of the galaxy’s spiraling arms.
Of the billions of stars in the Milky Way, the Sun is the star attraction in our solar system. The Sun provides Earth the heat energy it needs for living things to thrive. It also produces light, which plants need to carry out photosynthesis.
Gravity: Pulling Together
The Sun exerts a powerful force called gravityon Earth and the other planets. The Sun’s gravity holds the planets in their orbits. Earth has its own gravity, too. It pulls things down towards the ground instead of letting them fly off into the air. (Think of your feet every time you take a step.)
The Moon, Earth’s nearest neighbor and its only natural satellite, uses its gravity to make things happen on Earth. When the Moon pulls on Earth, it causes the oceans to bulge toward the Moon. The effect we see is the rising and falling of the oceans’ tides.
Back At the Beginning
Scientists believe that Earth, and the rest of the solar system, began to form about 4.5 billion years ago in a giant cloud of dust and gas. Over time, dust particles began to clump together. It probably took the clump that became Earth tens of millions of years to reach its current size. The young Earth had no water, no atmosphere, and no life-forms.
After millions of years, chemical reactions began to take place. These reactions resulted in the forming of oceans. Then according to the theory of evolution, single-celled life-forms similar to bacteria began to appear. That was about 3.5 billion years ago. More complex life-forms evolved. Fish began appearing about 500 million years ago. Plants took root about 420 million years ago. Between 370 and 230 million years ago amphibians, insects, and reptiles evolved.
Here Come the Dinosaurs –- and There They Go
Among the reptiles that evolved were dinosaurs. These lizard-like creatures varied greatly in size and weight. One of the smallest was the compsognathus, which was about the size of a large house cat. One of the largest dinosaurs was Argentinosaurus, which probably measured 35 m long and weighed about as much as 90 elephants. The first mammals, birds, and flowering plants also appeared during the Age of Dinosaurs.
About 65 million years ago, a large number of species, including dinosaurs, died out. Scientists are not certain what caused this massextinction. Many believe an asteroid smashed into Earth. Others believe the climate changed. However, new plants and animalscontinued to evolve after the mass extinction. One new animal species was Homo sapiens, or human beings, about 100,000 years ago.
Dinosaurs became extinct for unknown reasons. Theories exist, such as an asteroid hitting the earth, but it is not known to be true.©Don Davis, NASA
Feeling the Heat
Extinction is just one example of how Earth changes. Earth’s climate changes, too. Soon after Earth formed, it was very hot. It gradually cooled to temperatures that allowed life to exist. There have been times in Earth’s history when the climate was much colder than it is today. These periods are called ice ages. During an ice age, glacierscover much of Earth’s land.
Like a Cake with Lots of Layers
Earth is made of layers. The outermost layer is a blanket of gases called the atmosphere. The atmosphere stretches upward from Earth’s surface to about 300 km. The atmosphere contains gases that plants and animals need to survive, such as oxygen. It also helps keep Earth warm and protects it from harmful radiation from space.
Aerial view of Farewell Spit, New Zeland. Tidal mudflats, sandy beaches, and the wetlands are all part of the ecosystem in New Zeland.©NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team
Earth’s surface consists of land and water. The land is made of soil and rock. Earth’s oceans, lakes, waterways, groundwater, and glaciers form a layer called thehydrosphere. The hydrosphere makes up more than 70 percent of Earth’s surface. The biosphere consists of the parts of the atmosphere, land, and hydrosphere where living things make their homes.
A World of Natural Wonders
The Grand Canyon was formed with many layers of sedimentary rock. Sedimentary rocks form as a result of pressure and time, these are the horizontal bands of rocks you can see.©G. Ellis/GLOBIO.org
Earth’s climate changes and evolving history have resulted in many amazing natural wonders. In Asia, Mt. Everest rises above the other snowy peaks of the Himalaya Mountains. It is known as the “roof of the world,” because it is the highest mountain above sea level on Earth. It is 8,850 m tall, about the altitude where jet airplanes fly.
Another breathtaking feature of Earth’s landscape is the 1.6 kmdeep Grand Canyon in the southwestern United States. The Canyon took millions of years to form as the Colorado River gradually sliced its way through rock. Just off the coast of Australia is the Great Barrier Reef. The reef is made of the skeletons of tiny sea animals called corals. The Reef covers 350,000 km2, or roughly the same area as Germany. It is one of the largest structures ever “built” by nonhumans.
Dunes are created by winds blowing the sand, and the shape is created by how the wind interacts with the landscape. This Barchan dune in the Sahara desert is in the shape of an arc.©G. Ellis/GLOBIO.org
The world’s largest desert is the Sahara Desert in Africa. Measuring about 9 million km2, it is roughly the size of the United States. It is one of the driest and hottest places on Earth.
Variety Show: Earth's Life Forms
Earth’s biodiversity is as remarkable as its geography. Life on Earth ranges in size frommicroscopic single-celled animals such as amoebas to the giant sequoia trees of the western United States. The ecosystem with the most diverse life on Earth is the tropical rainforest. Tropical rainforests are thick with vines, ferns, shrubs, and trees. An incredible variety of animals live in the forests, too, including jaguars, parrots, monkeys, sloths, tree snakes, tree frogs, and thousands of species of insects. Scientists estimate that more than half of Earth’s plant and animal species live in tropical rainforests. In fact, scientists are still trying to identify and catalog them all.
The fur of a harp seal pup is white so it will blend into the ice and snow and be safer from prey. Seals have adapted to the cold climate of Antarctica with their thick layer of fat under the skin.©G. Ellis/GLOBIO.org
Adaptations Come in Handy
Plants and animals haveadaptations that help them survive in some of Earth’s harshest environments. For example, penguins, seals, and whales have thick layers of fat under their skin that help them stay warm in the icy temperatures of Antarctica. Grasses, shrubs, and small trees live in the Sahara Desert. They have adaptations such as water-storing leaf structures to help them survive in the heat and dryness.
Exploring Earth on Land, Sea, or from Space
Humans have always been curious about their home planet and eager to learn more about it. Some of Earth’s great explorers include Christopher Columbus, an Italian sailor who in 1492 sailed from Europe to the Americas. In 1519, the Portuguese explorer Ferdinand Magellan led the first voyage around the world. Mountaineers Edmund Hillary of New Zealand and Tenzing Norgay of Tibet became the first people to climb to the top of Mt. Everest in 1953.
Submersibles are used to explore the ocean. Lights and sophisticated camera equipment help the Deep Worker to record underwater scenery.©NOAA
Modern technology allows us to explore Earth in ways early explorers never could have dreamed were possible. Scientists explore the depths of the ocean usingsubmersibles and underwater robots. These technologies help them study ocean life, map the ocean floor, and locate ancient shipwrecks. Satellites launched into orbit above us collect data that can be used to forecast weather and make maps of Earth.
Spacecraft have helped scientists learn about Earth’s neighbors in the solar system. The spacecraft Voyager 1, for instance, has been traveling the solar system since its launch in 1977. Its powerful telescopes and cameras have sent tremendous amounts of data back to Earth. Voyager 1 will soon exit the solar system. Scientists can only guess what exciting new discoveries it will make.