EARTH’S SCIENCE
BY; BOLA-EFE ITSEKOR.
001: THE EARTH AND ITS COMPONENTS

Earth is the third planet in distance from the Sun in the solar system, the only planet known to
harbor life, and the “home” of human beings. About 71 percent of Earth’s surface is covered by
water, which is essential to life. The rest is land, mostly in the form of continents that rise above
the oceans. Earth is about 4.5 billion years old—that’s 4.5 followed by eight zeros, or 4,500
million years. In other words, it is really OLD. Geologists estimate the age of Earth by using a
geologic clock to date the rocks found on Earth. The clock is based on the natural radioactivity
within the rocks themselves.
Earth’s surface is surrounded by a layer of gases known as the atmosphere, which extends
upward from the surface, slowly thinning out into space. Below the surface is a hot interior of
rocky material and two core layers composed of the metals nickel and iron in solid and liquid
form.
Unlike the other planets, Earth has a unique set of characteristics ideally suited to supporting
life as we know it. It is neither too hot, like Mercury, the closest planet to the Sun, nor too cold,
like distant Mars and the even more distant outer planets—Jupiter, Saturn, Uranus, Neptune,
and the tiny dwarf planet Pluto and Eris. Earth’s atmosphere includes just the right amount of
gases that trap heat from the Sun, resulting in a moderate climate suitable for water to exist in
liquid form. The atmosphere also helps block radiation from the Sun that would be harmful to
life. Earth’s atmosphere distinguishes it from the planet Venus, which is otherwise much like
Earth. Venus is about the same size and mass as Earth and is also neither too near nor too far
from the Sun. But because Venus has too much heat-trapping carbon dioxide in its atmosphere,
its surface is extremely hot—462°C (864°F)—hot enough to melt lead and too hot for life to
exist.
Earth is the third planet from the Sun, after Mercury and Venus. The average distance between
Earth and the Sun is 150 million km (93 million mi). Earth and all the other planets in the solar
system revolve, or orbit, around the Sun due to the force of gravitation. The Earth travels at a
velocity of about 107,000 km/h (about 67,000 mph) which is about 30km/second as it orbits
the Sun. All but one of the planets orbit the Sun in the same plane—that is, if an imaginary line
were extended from the center of the Sun to the outer regions of the solar system, the orbital
paths of the planets would intersect that line. The exception is the dwarf planet Pluto, which
has an eccentric (unusual) orbit.
Earth is the fifth largest planet in the solar system. Its diameter, measured around the equator,
is 12,756 km (7,926 mi), it is small compared with the giant planets of the outer solar system—
Jupiter, Saturn, Uranus, and Neptune. For example, the largest planet, Jupiter, has a diameter
at its equator of 143,000 km (89,000 mi), 11 times greater than that of Earth. A famous
atmospheric feature on Jupiter, the Great Red Spot, is so large that three Earths would fit inside
it.
Earth has one natural satellite, the Moon. The Moon orbits the Earth, completing one
revolution in an elliptical path in 27 days 7 hr 43 min 11.5 sec. The Moon orbits the Earth
because of the force of Earth’s gravity. However, the Moon also exerts a gravitational force on
the Earth. Evidence for the Moon’s gravitational influence can be seen in the ocean tides
As Earth revolves around the Sun, it rotates, or spins, on its axis, an imaginary line that runs
between the North and South poles. The period of one complete rotation is defined as a day
and takes 23 hr 56 min 4.1 sec. The period of one revolution around the Sun is defined as a
year, or 365.2422 solar days, or 365 days 5 hr 48 min 46 sec. Earth also moves along with the
Milky Way Galaxy as the Galaxy rotates and moves through space. It takes more than 200
million years for the stars in the Milky Way to complete one revolution around the Galaxy’s
center.
The atmosphere is a layer of different gases that extends from Earth’s surface to the exosphere,
the outer limit of the atmosphere, about 9,600 km (6,000 mi) above the earth’s surface. Near
Earth’s surface, the atmosphere consists almost entirely of nitrogen (78 percent) and oxygen
(21 percent).
The layers of the atmosphere are the troposphere, the stratosphere, the mesosphere, the
thermosphere, and the exosphere. The troposphere is the layer in which weather occurs and
extends from the surface to about 16 km (about 10 mi) above sea level at the equator. Above
the troposphere is the stratosphere, which has an upper boundary of about 50 km (about 30
mi) above sea level. The layer from 50 to 90 km (30 to 60 mi) is called the mesosphere. At an
altitude of about 90 km, temperatures begin to rise. The layer that begins at this altitude is
called the thermosphere because of the high temperatures that can be reached in this layer
(about 1200°C, or about 2200°F). The region beyond the thermosphere is called the exosphere.
The thermosphere and the exosphere overlap with another region of the atmosphere known as
the ionosphere, a layer or layers of ionized air extending from almost 60 km (about 50 mi)
above Earth’s surface to altitudes of 1,000 km (600 mi) and more.
Earth’s atmosphere and the way it interacts with the oceans and radiation from the Sun are
responsible for the planet’s climate and weather. The atmosphere plays a key role in supporting
life. Almost all life on Earth uses atmospheric oxygen for energy in a process known as cellular
respiration, which is essential to life. The atmosphere also helps moderate Earth’s climate by
trapping radiation from the Sun that is reflected from Earth’s surface. Water vapor, carbon
dioxide, methane, and nitrous oxide in the atmosphere act as “greenhouse gases.” Like the
glass in a greenhouse, they trap infrared, or heat, radiation from the Sun in the lower
atmosphere and thereby help warm Earth’s surface. Without this greenhouse effect, heat
radiation would escape into space, and Earth would be too cold to support most forms of life.
Other gases in the atmosphere are also essential to life. The trace amount of ozone found in
Earth’s stratosphere blocks harmful ultraviolet radiation from the Sun. Without the ozone layer,
life as we know it could not survive on land.
EARTH’S SURFACE
Earth’s surface is the outermost layer of the planet. It includes the hydrosphere, the crust, and
the biosphere.
The Hydrosphere
The hydrosphere consists of the bodies of water that cover 71 percent of Earth’s surface. The
largest of these are the oceans, which contain over 97 percent of all water on Earth. Glaciers
and the polar ice caps contain just over 2 percent of Earth’s water in the form of solid ice. Only
about 0.6 percent is under the surface as groundwater. Nevertheless, groundwater is 36 times
more plentiful than water found in lakes, inland seas, rivers, and in the atmosphere as water
vapor. Only 0.017 percent of all the water on Earth is found in lakes and rivers. And a mere
0.001 percent is found in the atmosphere as water vapor. Most of the water in glaciers, lakes,
inland seas, rivers, and groundwater is fresh and can be used for drinking and agriculture.
Dissolved salts compose about 3.5 percent of the water in the oceans, however, making it
unsuitable for drinking or agriculture unless it is treated to remove the salts.
The Crust
The crust consists of the continents, other land areas, and the basins, or floors, of the oceans.
The dry land of Earth’s surface is called the continental crust. It is about 15 to 75 km (9 to 47 mi)
thick. The oceanic crust is thinner than the continental crust. Its average thickness is 5 to 10 km
(3 to 6 mi). The crust has a definite boundary called the Mohorovičić discontinuity, or simply
the Moho. The boundary separates the crust from the underlying mantle, which is much thicker
and is part of Earth’s interior.
Biosphere
The biosphere includes all the areas of Earth capable of supporting life. The biosphere ranges
from about 10 km (about 6 mi) into the atmosphere to the deepest ocean floor. For a long time,
scientists believed that all life depended on energy from the Sun and consequently could only
exist where sunlight penetrated. In the 1970s, however, scientists discovered various forms of
life around hydrothermal vents on the floor of the Pacific Ocean where no sunlight penetrated.
They learned that primitive bacteria formed the basis of this living community and that the
bacteria derived their energy from a process called chemosynthesis that did not depend on
sunlight. Some scientists believe that the biosphere may extend relatively deep into Earth’s
crust. They have recovered what they believe are primitive bacteria from deeply drilled holes
below the surface. The Earth’s interior is extremely hot. The core is almost 4000°C (7000°F). The
mantle of the Earth is somewhat cooler, around 1500°C (2700°F), depending on depth below
the surface.
EARTH’S FUTURE
With the rise of human civilization about 8,000 years ago and especially since the Industrial
Revolution in the mid-1700s, human beings began to alter the surface, water, and atmosphere
of Earth. In doing so, they have become active geological agents, not unlike other forces of
change that influence the planet. As a result, Earth’s immediate future depends to a great
extent on the behavior of humans. For example, the widespread use of fossil fuels is releasing
carbon dioxide and other greenhouse gases into the atmosphere and threatens to warm the
planet’s surface. This global warming could melt glaciers and the polar ice caps, which could
flood coastlines around the world and many island nations. In effect, the carbon dioxide that
was removed from Earth’s early atmosphere by the oceans and by primitive plant and animal
life, and subsequently buried as fossilized remains in sedimentary rock, is being released back
into the atmosphere and is threatening the existence of living things. See also Global Warming.
Even without human intervention, Earth will continue to change because it is geologically
active. Many scientists believe that some of these changes can be predicted. For example,
based on studies of the rate that the seafloor is spreading in the Red Sea, some geologists
predict that in 200 million years the Red Sea will be the same size as the Atlantic Ocean is
today. Other scientists predict that the continent of Asia will break apart millions of years from
now, and as it does, Lake Baikal in Siberia will become a vast ocean, separating two landmasses
that once made up the Asian continent.
In the far, far distant future, however, scientists believe that Earth will become an
uninhabitable planet, scorched by the Sun. Knowing the rate at which nuclear fusion occurs in
the Sun and knowing the Sun’s mass, astrophysicists (scientists who study stars) have calculated
that the Sun will become brighter and hotter about 3 billion years from now, when it will be hot
enough to boil Earth’s oceans away. Based on studies of how other Sun-like stars have evolved,
scientists predict that the Sun will become a red giant, a star with a very large, hot atmosphere,
about 7 billion years from now. As a red giant the Sun’s outer atmosphere will expand until it
engulfs the planet Mercury. The Sun will then be 2,000 times brighter than it is now and so hot
it will melt Earth’s rocks. Earth will end its existence as a burnt cinder. See also Sun.
Three billion years is the life span of millions of human generations, however. Perhaps by then,
humans will have learned how to journey beyond the solar system to colonize other planets in
the Milky Way Galaxy and find another place to call “home.”
Light travels at a speed of 300,000km/s.
The sun is about 150million kilometer from the earth.
Sun’s diameter is 1,392,000 km (865,000 mi).
The sun’s light takes about 8minutes to get to earth.
The earth rotates about 30km/s on its orbit.
A light year is the distance light travels in a year—9.5 trillion km, or 5.9 trillion mi.
The earth is made up of 71 percent water of which the water in the oceans takes about 97
percents. Major oceans in the earth includes; Atlantic Ocean, Pacific Ocean and Indian Ocean,
While minor oceans includes; southern ocean, Arctic Ocean e.t.c.
The Sun is located in the outer part of the galaxy, at a distance of 2.6 × 1017 km (1.6 × 1017 mi)
from the center. The Sun, which is moving around the center at a velocity of 220 km/s (140
mi/s), takes 250 million years to complete one trip around the center of the galaxy. The Sun has
circled the galaxy more than 18 times during its 4.6-billion-year lifetime.