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.
Size of the Earth compared to the Moon
Side by side comparison of the size of
Earth vs the Moon
Facts about Earth
- The Earth was once believed to be the centre 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. 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. 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. 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 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.
More information and facts about Earth
Throughout human history we have sought to understand our home planet.
However, the learning curve has been steep, with many errors having been made
along the way. For example, it was not until the time of the ancient Romans
that the world was understood to be spherical rather than flat. A second
example is the belief that the Sun revolved around the Earth. Only in the
sixteenth-century, through the work of Copernicus, did we accept that,
in fact, the Earth was merely a planet orbiting the Sun.
Perhaps most importantly, it is during the last two centuries that science
has allowed us to see that the Earth is both an ordinary and unique place in the Solar System. On one hand, many of its
characterisitcs are rather unexceptional. Take, for example, its size,
interior, and geological processes—being the fifth largest out of the
eight planets, it is close to the median in terms of size; its interior
structure is almost identical to the three other terrestrial planets; and the
same geological processes that shape its surface can be found not only on other
planets, but also on planetary moons. However, the Earth is special in one very
important regard—in all of the solar system, the Earth is the only
world known to foster life.
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. Essentially, this means that
without plants the amount of carbon dioxide in the atmosphere would be much
greater and the oxygen levels much lower. On one hand, if carbon dioxide levels
were much higher, it is likely the Earth would suffer from a runaway greenhouse
effect like that on Venus. On the other hand, if the percentage of
carbon dioxide were any lower there would not be a greenhouse effect at all,
thus making temperatures far colder. Therefore, the carbon dioxide levels are
just right to maintain hospitable temeperatures ranging from -88° C to 58° C.
Oceans
When viewing Earth from space, there is one overwhelming feature—the
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 wintin the Earth during its formation. Over time, the planet’s
geological mechanisms, primarily its volcanic activity, released this water
vapor into the atmosphere. Once in the atmosphere, this vapor condensed and
fell to the planet’s surface as liquid water. The second source is theorized to
have originated from the ancient comets that
struck the Earth. Upon impact, they deposited substantial amounts of water ice
on the planet.
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.
Thus, impact craters have been “smoothed out” through weathering and
erosion by being broken apart and redistributed to other areas on the Earth’s
surface.
Two other geological mechanisms have helped to shape the Earth’s surface.
The first is volcanic activity. This process consists of the releasing of magma
(molten rock) from the Earth’s interior through a rupture in the its crust.
Some effects of volcanic activity can be the resurfacing of Earth’s crust or
formation of islands (think of the Hawaiian Islands). The second mechanism is
orogeny, or the formation of mountains through the compression of tectonic
plates. An example of mountains created through this process is the Rocky
Mountains.
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.
Yet another distinguishing feature of the Earth when compared to the other
terrestrial planets is that its crust is divided into cool, rigid plates that
rest upon the hotter mantle below. Furthermore, these plates are in constant
motion. Along the boundaries of these plates two processes, known as subduction
and spreading, can occur. During subduction two plates come into contact
(sometimes violently, producing earthquakes) and one plate is forced under the
other. Separation, on the other hand, is when two plates are moving away from
each other.
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.
The Earth’s axial tilt is approximately 23.45°. That is, the axis the Earth
rotates about is tilted slightly with respect to the plane in which the Earth
orbits the Sun. The effect of this tilt, along with position of the Earth in
its orbit, means that at certain times the amount of sunlight the northern
hemisphere receives is greater than that of the southern hemisphere, and vice
versa. This variation in intensity is what produces the warmer temperatures
during the summer and colder temperatures during the winter.
A second commonly know charecteristic is that the Earth takes approximately
twenty-four hours to complete one rotation. This is fastest among the
terrestrial planets, but easily slower than that of all the gas planets.
Source: http://theplanets.org/earth/
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