What Is Earth?  Earth is the third planet from the Sun and largest of the terrestrial planets. Surprisingly, while it is only the fifth largest planet in terms of size and mass, it is the densest (5,513 kg/m3) of all the planets. Earth is the only planet in the solar system not named after a mythological being. Instead, its name is derived from the Old English word "ertha" and the Anglo-Saxon word "erda" which means ground or soil.  Earth was formed somewhere around 4.54 billion years ago and is currently the only known planet to support life - and lots of it.

EARTH PROFILE Mass5,972,190,000,000,000 billion kg Equatorial Diameter12,756 km Polar Diameter 12,714 km Equatorial Circumference40,030 km Known Moons1 Notable Moons : The Moon Orbit Distance149,598,262 km (1 AU) Orbit Period Earth Days Surface Temperature

SIZE OF THE EARTH COMPARED TO THE MOON Side by side comparison of the size of Earth vs the Moon

THE EARTH WAS ONCE BELIEVED TO BE THE CENTER OF THE UNIVERSE. For 2000 years ancient astronomers believed that the Earth was static and had other celestial bodies travelling in circular orbits around it. They believed this because of the apparent movement on the Sun and planets in relation to their viewpoint. In 1543, Copernicus published his Sun-centered model of the Solar System which put the Sun at the centre of our solar system.

EARTH IS THE ONLY PLANET NOT NAMED FOR A MYTHOLOGICAL GOD OR GODDESS EARTH IS THE ONLY PLANET NOT NAMED FOR A MYTHOLOGICAL GOD OR GODDESS. The other seven planets in the solar system were named after Roman gods or goddesses. For the five visible to the naked eye, Mercury, Venus, Mars, Jupiter and Saturn they we named during ancient times. This Roman method was also used after the discovery of Uranus and Neptune. The word “Earth” comes from the Old English word “ertha” meaning ground or land.

 Earth is the most dense planet in the solar system  Earth is the most dense planet in the solar system. The density of Earth differs in each part of the planet – the core, for example, is denser than the Earth’s crust – but the average density of the planet is around 5.52 grams per cubic centimetre.  The gravity between the Earth and the Moon causes the tides on Earth  The gravity between the Earth and the Moon causes the tides on Earth. This effect on the Moon means it is tidally locked to Earth – its rotation period is the same as its orbit time so it always presents the same face to Earth.  The rotation of the Earth is gradually slowing down  The rotation of the Earth is gradually slowing down. The deceleration of the Earth’s rotation is very slow, approximately 17 milliseconds per hundred years. Eventually this will lengthen our days but it will take around 140 million years before our day will have increased from 24 to 25 hours.

 Earth’s atmosphere is composed of 78% nitrogen, 21% oxygen, and trace amounts of other gases including argon and carbon dixoide.  The large amount of oxygen on Earth comes from our plant life’s consumption of carbon dioxide during photosynthesis.  Earth has a very powerful magnetic field. This field protects the planet from the effects of solar winds and is believed to be a result of the nickel-iron core of the planet combined with its rapid rotation.  The Earth has an Ozone Layer which protects it from harmful solar radiation. This shell is a special type of oxygen that absorbs most of the Sun’s powerful UV rays.  70% of the Earth’s surface is covered by water – the remainder consists of continents and islands which together have many lakes and other sources of water.

 The first life on Earth developed in the oceans through a process called abiogenesis or biopoiesis. This is a natural process in which life grows from non-living matter like simple organic compounds.  Earth’s water was initially trapped within the planet. Over time the Earth’s water was brought to the surface by the planet’s volcanic activity.  Earth has relatively few visible impact craters compared with other solid bodies in our solar system. This is because Earth is geologically active and has processes like tectonics and erosion that reshape its surface.  The highest point found on Earth is Mount Everest which reaches a height of 8.8 km.

 The lowest point on Earth is called Challenger Deep and at 10.9 km below sea level, it is further than the peak of Mount Everest.  Earth has one of the most circular orbits of all the eight planets. Its axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, which produces the seasons we experience.  A year on Earth lasts just over 365 days. It is actually 1/4 of a day over 365 days which is why we have a leap year every four years.

ATMOSPHERE The ability for Earth to possess life is dependent in many ways on its atmosphere. The composition of the atmosphere is roughly 78% nitrogen (N2), 21% oxygen (O2), 1% argon, with trace amounts of carbon dioxide (CO2) and other gases. Nitrogen and oxygen are essential to DNA and biological energy production, respectively, without which life could not be sustained. Additionally, the oxygen found in what is known as the ozone layer of the atmosphere protects the surface of the planet by absorbing harmful solar radiation. Remarkably, the significant amount of oxygen present in the atmosphere is due to the life found on Earth. As a byproduct of making sugars, plants convert the carbon dioxide in the atmosphere into oxygen.

OCEANS When viewing Earth from space, there is one overwhelming feature&#8212the oceans of liquid water. In terms of surface area, these oceans cover approximately 70% of the Earth. What is even more amazing than this percentage is that a single drop of liquid water is yet to be found on any other planet in the Solar System. In this regard, the Earth is truly unique. Like the Earth’s atmosphere, the presence of liquid water is vital for life. In fact, life is believed to have first developed 3.8 billion years ago in the oceans, only later evolving the ability to survive on land. The existence of the oceans is attributed to two sources. The first of these is the Earth itself. It is conjectured that large amounts of water vapor were trapped within the Earth during its formation. Over time, the planet’s geological mechanisms, primarily its volcanic activity, released this water vapor into the atmosphere.

SURFACE Although most of the Earth’s surface lies beneath its oceans, the remaining “dry” surface is quite remarkable. When comparing the Earth to other solid bodies in the Solar System, its surface stands out due to its lacking impact craters. It is not that the Earth has been spared the numerous impacts by small bodies; rather, it is because the evidence of these impacts has been erased. Although there are many geological processes responsible for this, the two most important are weathering and erosion. In many ways these two mechanisms can be thought of as working in tandem. Weathering is the breaking down of surface structures into smaller pieces by the atmosphere. Moreover, there are two types of weathering: chemical and physical. An example of chemical weathering is acid rain. An example of physical weathering is abrasion of river beds caused by rocks suspended in flowing water. The second mechanism, erosion, is simply the movement of weathered particles by water, ice, wind or gravity.

INTERIOR Similar to the other terrestrial planets, Earth’s interior is believed to consist of three components: a core, a mantle, and a crust. At present, the core is thought to be comprised of two separate layers& an inner core composed of solid nickel and iron, and an outer core composed of molten nickel and iron. The mantle is very dense and almost entirely solid silicate rock; its thickness is roughly 2,850 km. Finally, the crust is also composed of silicate rock and varies in thickness. While the continental crust ranges from 30 to 40 km in thickness, the oceanic crust is much thinner at only 6 to 11 km.

ORBIT & ROTATION At roughly 365 days, the Earth’s orbit around the Sun is familiar to us. The length of our year is due in large part to the Earth’s average orbital distance of 1.50 x 108 km. What many people are not familiar with is that at this orbital distance it takes sunlight, on average, about eight minutes and twenty seconds to reach the Earth. With an orbital eccentricity of.0167, the Earth’s orbit is one of the most circular in all the Solar System. This means that the difference between Earth’s perihelion and aphelion is relatively small. As a result of this small difference, the intensity of the sunlight Earth receives remains almost constant year-round. However, the Earth’s position in its orbit is responsible, in part, for the varying seasons it experiences.