Earth

The third planet out from the Sun,
the Earth is 93Â½ million miles away from on average.

Earth

fifth largest planet in the Solar system.
a diameter of 7,972Â½ miles and a circumference of 25,046 miles at the equator.
along with Mercury, Venus and Mars – Earth is one of four rocky planets; it is made mostly rocky with a core of iron and nickel.
no other planet in the Solar System has liquid water on its surface – Earth is uniquely suitable for life.
more than 70% of Earth’s surface is underwater.
atmosphere is mainly harmless nitrogen and life-giving oxygen; 125 miles deep.
oxygen has been made and maintained by plants over billions of years.
magnetic field – stretching 37,500 miles out into space for protects from the Sun’s Radiation.
Earth’s orbit around the Sun is 587Â½ miles in length and takes 365Â¼ days.
although the Earth is tilted at an angle of 23Â½ degrees – orbits the Sun on a level plane; the plane of the ecliptic.
Earth is made up of the same materials as meteorites and the other rocky planets – mostly iron (35%), oxygen (28%), silicon (17%), magnesium (15%) and nickel (2.7%).

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Earth’s formation

solar system was created Â when the gas cloud left over from a giant supernova explosion started to collapse in in itself and spin.
around 4Â¾Â billion years ago – only a vast hot cloud of dust and gas circling a new star; our Sun was existed.
Earth might began when tiny pieces of space debris (planetesimals) were pulled together by each other’s gravity.
as the earth formed – more space debris kept on smashing into it, adding new material – this debris included ice from the edges of the Solar System.
about 4Â½ billions years ago – rock the size of Mars crashed into the earth; this debris joined together to form the Moon.
this collision that created the Moon made the Earth very hot.
radioactive decay heated the Earth even more.
for a long time – the surface of the earth was a mass of erupting volcanoes.
heavy materials – iron and nickel melted and sank to form the core.
lighter materials – aluminium, oxygen and silicon, floated up and cooled to form the crust.

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Earth’s atmosphere

blanket of gases – we call it air that extends from the planet’s surface up to a height of about 60 miles.
most of the air is concentrated in the lowest part of the atmosphere the air gets changing thinner with increasing attitude – around above 7,000 metres, there is not enough oxygen for people to breathe.
near the surface, our atmosphere consists of nitrogen (78%), oxygen (21%) and small amounts of argon, carbon dioxide and other gases, together with a variable amount of water vapour.
atmosphere – divided into a series of layers that have different characteristics.
troposphere – the lowest level; extends up to around 6 miles above the sea level ~ the weather and human activity are largely restricted to the troposphere.
stratosphere – Â extends from 6 miles to around 30 miles in altitude, and contains the ozone layer that shields earth’s surface from the harmful ultraviolet (UV) radiation on sunlight.
mesosphere – above the stratosphere, most meteors that are seen burn up in the mesosphere (30 to 50 miles). (sometimes, it’s called the upper stratosphere.)
exosphere – the uppermost level of the atmosphere; extends between 50 and 250 miles above stratosphere.

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Earth’s ionosphere

ionosphere – around a planet that contains atoms and molecules that have been ionized by strong X-rays and UV light.
extends from around 30 miles above the sea level out beyond the atmosphere to about 600 miles; the ionosphere contains a series of distinct layers (Heaviside Layer) that are used to reflect radio signals around the planet.

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