By earth I am referring to the planet Earth, also known as
the world, Terra or Gaia. The standard astronomical symbol of the Earth
consists of a cross circumscribed by a circle,
. It is the
third planet from the sun. The planet Earth is the densest planet in the solar
system, the largest of the solar system’s four terrestrial planets(other three
terrestrial planets- Mercury, Venus and Mars) , and the only celestial body
known to accommodate life.
It is home to untold number of species, including billions of
humans who depend on its biosphere and minerals.
Earth is regarded as a terrestrial planet because it is a
rocky body, rather than a gas giant like Jupiter. Earth gravitationally interacts with other
objects in space, especially the Sun and the Moon. During orbit around the Sun,
the Earth rotates about its own axis 366.26 times, creating 365.26 solar days,
or one sidereal. The Moon is Earth’s only natural satellite. The moon orbits
the earth.
The mass of the Earth is approximately 5.98 × 10²⁴ kg in
scientific notation and 5,972,190,000,000,000,000,000,000 kg in metric terms.
It is composed of iron (32.1%), oxygen (30.1%),
silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%)
and aluminum (1.4%); with the remaining 1.2% consisting of trace amounts of
other elements. 70.8% of the Earth’s surface is covered by water. The abundance
of water on the earth’s surface is a unique feature that distinguishes the
“Blue Planet” from others in the Solar System.
Crib is defined as a
small habitation or cottage. Cottage is a cot or small house. A meaning from
Urban Dictionary is: ….place of residence, where you live, and where you were
raised.
Earthling means an inhabitant of the earth. The Oxford
Advance Learner’s Dictionary defines the word earthling as: a word used in
SCIENCE FICTION stories by creatures from other planets to refer to a person
living on earth.
When I put the three terms together, I am simply saying the
planet Earth is a relatively small abode for man in the cosmos.
Why is it man can dwell on planet Earth only? Why not Jupiter
or Neptune? What is so special about Earth that makes it habitable for man?
According to evidence from
sources such as radiometric dating, Earth was formed around
four and a half billion years ago. Within its first billion years,[32]
life
appeared in its oceans and began to affect its atmosphere and surface, promoting the
proliferation of aerobic as well as anaerobic organisms and causing the formation of
the atmosphere's ozone layer. This layer and Earth's magnetic field block the most
life-threatening parts of the Sun's radiation, so life was able to flourish on land as
well as in water.[33]
Since then, Earth's position in the Solar System, its physical
properties and its geological history have allowed
life to persist.
Earth's biosphere has significantly altered its atmosphere.
Oxygenic photosynthesis evolved 2.7 bya, forming the primarily nitrogen–oxygen
atmosphere of today.[108] This change enabled the proliferation of aerobic
organisms as well as the formation of the ozone layer which blocks ultraviolet
solar radiation, permitting life on land. Other atmospheric functions important
to life on Earth include transporting water vapor, providing useful gases,
causing small meteors to burn up before they strike the surface, and moderating
temperature. This last phenomenon is known as the greenhouse effect: trace
molecules within the atmosphere serve to capture thermal energy emitted from
the ground, thereby raising the average temperature. Water vapor, carbon
dioxide, methane and ozone are the primary greenhouse gases in the Earth's
atmosphere. Without this heat-retention effect, the average surface would be
−18 °C, in contrast to the current +15 °C, and life would likely not exist.
Earth is unique among the known
planets: it has an abundance of water. Other worlds — including a few moons —
have atmospheres, ice, and even oceans, but only Earth has the right
combination to sustain life.
Personification of planet Earth:
Earth or soil - flesh
Rock - bones
Water - blood
Atmosphere - the air it breathes
Forest – lungs, purifies the air
The summary is that the planet Earth is a relatively small
dwelling place for man, compared to the cosmos at large, as a crib is, in
relation to other dwelling places on Earth. By peculiar conditions set on Earth
to engender life, man can’t live elsewhere in the known cosmos. Hence, man is
Earthbound.
Reference:
en.wikipedia.org/wiki/Earth
The New Webster Dictionary of the English Language- 1965
www.en.wikipedia.org/wiki/Earth_mass
Urban Dictionary
www.space.com
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