Earth is one of the eight planets that orbit the Sun in our Solar System. It is the third planet from the Sun, between Venus and Mars, and the fifth largest planet in the Solar System. Earth is a terrestrial planet, and it is the largest among the terrestrial planets in the Solar System.
Earth is the planet that we live on, and it is the only planet in the Solar System that supports life. This is because it has two important things that living creatures need, which are oxygen and water. In addition, Earth’s temperatures are suitable for creatures to survive. The average distance between the Sun and Earth is about 150,000,000 kilometres / 93,000,000 miles.
The shape of Earth is not a perfect sphere because it is slightly squashed on the top and bottom. The shape is called an oblate spheroid. This is because Earth’s rotation around its center is fast.
Earth is the fifth largest planet in the Solar System, and the largest among terrestrial planets. Its diameter is 6.371 kilometers. It is almost three times bigger than Mercury. When it comes to Venus, it has about 94% of Earth’s diameter. Mars is nearly half the size of Earth. Jupiter, which is the biggest planet in the solar system, has more than 11 times the diameter of Earth. Saturn is 9.5 times the Earth’s diameter, and Uranus and Neptune are both four times bigger than Earth.
The Earth is made up of three layers: the core, the mantle, and the crust.
The Earth’s surface is either water or land.
Land covers about 30 percent of Earth’s surface, and it is divided into seven huge pieces called continents. These continents are Asia, Africa, Europe, North America, South America, Australia, and Antarctica. Generally, all places on Earth are made of, or on top of, rocks. However, the land on Earth is not even. There are different kinds of terrain on Earth’s surface. For example, there are high places called mountains, high flat places called plateaus, and low places called valleys and canyons.
Water covers about 70 percent of Earth’s surface. Water on Earth exists in the form of oceans, rivers, lakes, and groundwater. The five oceans on Earth are: the Arctic, Southern, Indian, Atlantic and Pacific. The oceans surround the continents. Some water is frozen, such as the large ice sheets in the Arctic and Antarctic regions.
The atmosphere is a layer of different gases that surrounds the Earth. It goes up to a few hundred miles above the surface, and it gets thinner as it gets farther from the surface. The atmosphere of Earth consists of 77% nitrogen, 21% oxygen, traces of water vapor and other gases.The atmosphere helps maintain temperatures on Earth so that they are warm enough for living creatures to survive. The atmosphere also protects the Earth from meteoroids that come from outer space. Most meteoroids break up in the atmosphere before they can reach the surface.
At the surface of Earth, the average temperature of the atmosphere is 14 °C (57 °F). The atmosphere is hot in parts and cold in others, depending on the height. These changes of temperatures according to height are divided into layers. So, the difference between the layers is how the temperatures change. These are the layers of the atmosphere:
This layer starts at the ground and ends somewhere between 0 to 18 kilometres. In this layer, there is the air that living creatures breathe. The day to day changes of air are named the weather. The changes between places far away from each other and over a long period of time are named the climate. Atmospheric conditions, such as rain and storms, happen in the Troposphere layer. Finally, the higher in this layer, the colder the air gets.
This layer starts at 18 kilometres (11 miles) and ends at 50 kilometres (31 miles). The higher in this level, the hotter it gets. The heat comes from a special kind of oxygen, called ozone, that is found at the top of the stratosphere. The ozone also keeps living things safe from damaging rays from the Sun. Airplanes fly in this layer because it is usually stable and the air resistance is little.
This layer starts at 50 kilometres (31 miles) and ends at 80 or 85 kilometres (50 or 53 miles). The higher in this layer, the colder it gets. The temperature is not stable in the Mesosphere layer because the winds are strong.
This layer starts at 80 or 85 kilometres (50 or 53 miles) and ends at 640 kilometres (400 miles) or higher. The higher in this level, the hotter it gets. Temperatures are high in the Thermosphere layer because it absorbs X-rays and extreme ultraviolet radiation from the Sun. This layer helps reflect some radio waves, which helps in radio communication.
This is the top layer. It is almost outer space, and it reaches about half the way to the Moon. The Exosphere has very little air.
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Earth, like all planets, has two types of motion: orbit around the Sun, and spin, or rotation, around its centre. Earth orbits, or travels around, the Sun at an average speed of 30 kilometres per second. It takes Earth 365.25 days to orbit the Sun once. So, one year on Earth should be 365.25 days, but our calendar system counts one year as 365 days. To make up this extra quarter of a day, every four years we add one day. That day is called a leap day, and the year it is added to is called a leap year.
Earth also spins, or rotates, about its center. This results in daytime and nighttime. As Earth rotates, the side facing the sun receives daylight while the other side becomes in darkness. Earth completes one rotation in 24 hours. So, a day on Earth lasts for 24 hours.
Spring, Summer, Fall and Winter… Have you ever wondered why we have different seasons?
It is because Earth is tilted 23.4 degrees on its axis of rotation. This makes different parts of Earth tilted towards the sun at different times of the year. In other words, the northern hemisphere is tilted toward the Sun for part of the year, while the southern hemisphere is tilted away. With the Sun up in the sky, heat is greater in the north producing summer there, while it is less in the south producing winter there. After six months, the situation is reversed. When spring and fall begin, both hemispheres receive almost equal amounts of heat from the Sun.
Earth has only one natural satellite that is orbiting it, and it is called the Moon. The average distance between the Moon and Earth is 400,000 kilometres or 250,000 miles. The Moon orbits Earth in about 27 days, but because Earth orbits the Sun at the same time, it takes the Moon about 29.5 days to go from dark to bright to dark again. This is equal to one month on Earth, and this is where the word “month” came from, even though most months now have 30 or 31 days. The Moon is locked to Earth. This means that we always see the same side of its surface, and the other side is called the dark side.
Unlike other planets, Earth is not named after ancient gods. The name Earth is a Germanic word, which simply means “the ground.” The origin of the word is the Anglo-Saxon word “erda” which means “soil.” It later became “eorthe” and then “erthe” in Middle English. The word “Earth” was used for the first time as the name of our planet in the early 15th century. Sometimes, the word “Globe” is used to refer to Earth. The word “world” is also used to refer to Earth and all life that exists on it.
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