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Earth is the only planetary body in the solar system that has conditions suitable for life ( at
least as known to modern science). It is the third planet in distance outward from the Sun.
The mean distance of the Earth from the Sun is about 149,573,000 km. The planet orbits the
Sun at a speed of 29.8 km per second, making one complete revolution in 365.25 days. As it
revolves around the Sun, the Earth spins on its axis and rotates completely once every 23
hours 56 minutes and 4 seconds. The Earth is the fifth largest planet of the solar system. The
planet‘s total surface area is roughly 509,600,000 sq km, of which about 29 percent is land. It
has a single natural satellite, the Moon. The Earth has a shape of an oblate spheroid, being
flatter near the poles than near the Equator.
The Earth´s gravity is not fixed, but rather varies from place to place on the surface
(it is higher at the poles). The Earth´s atmosphere consists of a mixture of gases, chiefly
nitrogen (78 %) and oxygen (21%). The rest are argon, water vapour, carbon dioxide and various
other gases. The Earth is the only planet known to have liquid water. Together with ice, the
liquid water constitutes the hydrosphere. Sea water makes up more than 98 % of the total
mass of the hydrosphere and covers about 71 % of the Earth´s surface. The Earth´s surface is
divided into seven continents: Europe, Asia, Africa, North America, South America, Australia
and Antarctica. The World Ocean is broken down into three major oceans: the Atlantic, Pacific
and Indian oceans.
The Earth is surrounded by a magnetosphere, a region of strong magnetic forces that extends
upward from about 140 km in the upper atmosphere. In the magnetosphere, the magnetic field
of the Earth traps rapidly moving charged particles, the majority of which appear to be
emitted by the Sun during periods of intense activity. If it were not for this shielding effect,
such particles would bombard the terrestrial surface and destroy life.
The Solar System is made up of all the planets that orbit our Sun. In addition to planets, the
Solar System also consists of moons, comets, asteroids, minor planets, and dust and gas.
Everything in the Solar System orbits or revolves around the Sun. The Sun contains around
98% of all the material in the Solar System. The larger an object is, the more gravity it has.
Because the Sun is so large, its powerful gravity attracts all the other objects in the Solar
System towards it. At the same time, these objects, which are moving very rapidly, try to fly
away from the Sun, outward into the emptiness of outer space. The result of the planets trying
to fly away, at the same time that the Sun is trying to pull them inward is that they become
trapped half-way in between. Balanced between flying towards the Sun, and escaping into space,
they spend eternity orbiting around their parent star.
How Did The Solar System form?
Scientists believe that the Solar System evolved from a giant cloud of dust and gas. They believe that
this dust and gas began to collapse under the weight of its own gravity. As it did so, the matter
contained within this could begin moving in a giant circle, much like the water in a drain moves around the
center of the drain in a circle.
At the center of this spinning cloud, a small star began to form. This star grew larger and larger as it
collected more and more of the dust and gas that collapsed into it.
Further away from the center of this mass where the star was forming, there were smaller clumps of
dust and gas that were also collapsing. The star in the center eventually ignited forming our Sun, while
the smaller clumps became the planets, minor planets, moons, comets, and asteroids.
Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of
sugar. This process occurs in plants and some algae. Plants need only light energy, CO2, and H2O to make
sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the
green pigment involved in photosynthesis.
Photosynthesis takes place primarily in plant leaves.
Chlorophyll looks green because it absorbs red and blue light, making these colours unavailable to be seen
by our eyes. It is the green light which is NOT absorbed that finally reaches our eyes, making chlorophyll
appear green. However, it is the energy from the red and blue light that are absorbed that is, thereby,
able to be used to do photosynthesis. The green light we can see is not/cannot be absorbed by the plant,
and thus cannot be used to do photosynthesis.
The overall chemical reaction involved in photosynthesis is: 6CO 2 + 6H2O (+ light energy) C6H12O6 + 6O2.
This is the source of the O2 we breathe, and thus, a significant factor in the concerns about
deforestation.
The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from
the land to the sky and back again.
The Sun's heat provides energy to evaporate water from the Earth's surface (oceans, lakes, etc.). Plants
also lose water to the air (this is called transpiration). The water vapor eventually condenses, forming
tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is
triggered, and water returns to the land (or sea). Some of the precipitation soaks into the ground. Some
of the underground water is trapped between rock or clay layers; this is called groundwater. But most of
the water flows downhill as runoff (above ground or underground), eventually returning to the seas as
slightly salty water.
As water flows through rivers, it picks up small amounts of mineral salts from the rocks and soil of the
river beds. This very-slightly salty water flows into the oceans and seas. The water in the oceans only
leaves by evaporating (and the freezing of polar ice), but the salt remains dissolved in the ocean - it does
not evaporate. So the remaining water gets saltier and saltier as time passes.
Oceans cover about 70% of the Earth's surface. The oceans contain roughly 97% of the Earth's water
supply
Climate is defined as the weather conditions in a certain geographical area averaged over a long period
of time, typically 30 years. The climate's determination is carried out using annual and monthly
statistical measurements of local atmospheric data such as : temperature, precipitations, sun
exposure, humidity, wind's speed . The earth can be divided into several major climatic zones and bands:
Tropical / Subtropical / Arid / Equatorial / Semiarid / Mediterranean / Temperate / Oceanic /
Continental / Subarctic / Polar / climates and Climate of Antarctica
NATURAL DISASTERS
Earthquake is a tectonic or volcanic disturbance within the Earth. The passage of seismic
waves through the Earth often causes violent shaking of its surface. The origin of most major
earthquakes can be explained in terms of the plate tectonics theory. The location of the
earthquake is determined with a seismograph. The magnitude of an earthquake is usually
expressed in terms of the Richter scale. The scale is so arranged that each increase in
magnitude of one unit represents a tenfold increase in earthquake size, i.e. an earthquake of
Richter magnitude 8 is 10,000 times as large as one of magnitude 4.
Large earthquakes have caused some of the worst disasters in history. No other natural
phenomenon is as destructive over so large an area in so a short time. People are crushed and
buried under the collapsing structures or are burned to death in fires. Destructive, too, are the
landslides and mudslides that occasionally accompany an earthquake. Much research has been
devoted to earthquake prediction since the mid 1960s, but no method has yet been deviced to
predict the time, place or magnitude of quakes. Seismologists have found that major
earthquakes are often preceded by certain measurable physical changes in the environment
around their epicentres.)
Flood is a high-water stage in which water overflows its natural or artificial banks. Floods
commonly results from excessive rainfall over short periods of time, and also from ice jams
during the spring rise and from tsunamis (the mountainous sea waves caused by earthquakes)
Famine is an extreme shortage of food, causing widespread and persistent hunger. The causes
of famine are numerous, but they are usually divided into natural (drought, heavy rain and
flooding, typhoons, plant disease and insect infestations; drought being the most common
natural cause) and human categories (mainly warfare = destroying crops and food supplies and
blockade tactics, overpopulation) Famine continues to be a problem in parts of Latin America,
Central Africa and Southeast Asia. The effects of modern famines have been lessened by
international relief organizations.
Volcanic eruption, hurricane, forest fire, tsunami, avalanche, tornado
Our Sun is not unique in the universe. It is a common middle-sized yellow star which scientists have
named Sol, after the ancient Roman name. This is why our system of planets is called the Solar System.
There are trillions of other stars in the universe just like it. Many of these stars have their own systems
of planets, moons, asteroids, and comets.
The Sun was born in a vast cloud of gas and dust around 5 billion years ago. Over a period of many millions
of years, this gas and dust began to fall into a common center under the force of its own gravity.
At the center, an ever growing body of mass was forming. As the matter fell inward, it generated a
tremendous amount of heat and pressure. As it grew, the baby Sun became hotter and hotter. Eventually,
when it reached a temperature of around 1 million degrees, its core ignited, causing it to begin nuclear
fusion.
When this happened, the Sun began producing its own light, heat, and energy.
We don't often think of the Sun as having cooler areas on its surface. The Sun is far too hot for an
astronaut to ever visit, but there are areas which are slightly cooler than others. These areas are known
as sun spots. Sun spots are still very hot. However, because they are slightly cooler than the rest of the
surface of the Sun, they appear slightly darker in color. The gravitational forces in Sun spots are also
stronger than the other hotter areas. Of course, you cannot look directly at the Sun to see these spots
because you would damage your eyes. Astronomers have to use special telescopes with filters and other
instruments to be able to see the cooler spots on the surface of the Sun.
During periods of high solar activity, the Sun commonly releases massive amounts of gas and plasma into
its atmosphere. These ejections are known as solar flares. Some solar flares can be truly massive, and
contain impressive power. On occasion, these more powerful flares can even cause satellites orbiting the
Earth to malfunction. They can also interact with Earth's magnetic field to create impressive and
beautiful light shows known as the Northern and Southern lights. As the Sun burns hydrogen at its core,
it releases vast amounts of atomic particles, or pieces of atoms, into outer space. These atomic particles
along with the Sun's radiation create a sort of wind, known as the solar wind.
This wind blows particles outward in all directions from the Sun. Even as you read this, there are atomic
particles which are traveling from the Sun towards you. Often, particles pass right through your body
without you ever realizing it.
The Sun is by far the largest object in the Solar System. 98% of all matter within the Solar System is
found within the Sun. This means that all the planets, moons, asteroids, minor planets, comets, gas, and
dust would all combine to make up only 2% of all the matter in the Solar System. The Sun is so large that
the Earth could easily fit inside the Sun a million times.
Because the Sun is so large compared to everything else, it is easily able to hold on to the rest of the
matter, causing everything else to orbit around it.
Light from the Sun can reach the Earth in only 8 minutes! This is called the speed of light. The Sun is
nearly 93 million miles (approx 145 million km) from Earth.