Topic 2: The Planet Earth (New Syllabus Explained)
Topic 2: The Planet Earth (New Syllabus Explained)
CHAPTER 2 The planet earth
The earth is the only known planet in the solar system that supports life. Its surface is made up of land and water bodies .The evolution of the earth can be traced through various assumption including both theories and hypothesis which explain about the origin of the universe.
Some of the assumption that explain about the origin of the earth include
- Big bang theory
- Nebula hypothesis
- Inter-stellar dust hypothesis
- Creation theory
Nebular hypothesis
It explains about the origin of the earth. It was proposed by Immanuel Kant in 1755. The hypothesis states that solar system was formed from cold spinning cloud of gases called the solar nebular. It resulted from an even distribution of gases throughout the universe in the Milky Way galaxy. As the gravitation pull began to condense the gas towards the centre the speed of the rotation increased. This caused the cloud to flatten and created an accretion disk. Matter continued to collect as the force of gravity towards the centre increased. Eventually the gas warmed from increasing pressure, as the mass further increased, also the gravity increased and the temperature continued to rise. A ball of hot gas formed in the centre of accretion disk, creating a proto star also known as the sun. Finally when enough gas gathered in the centre of the protostar the pressure generated enough heat to fuse the atoms to form a star. Outside the star, matter was forming into clumps of gas, dust and rocks which created protoplanets that are believed to give rise to the planets. The theory was modified by Pierre Laplace in 1796.
The critiques of the theory were put forward by Pierre Laplace who challenged Immanuel Kant through the following;
- Larger amount of heat cannot be generated due to the collision of cold particles of primordial matter as claimed by Kant.
- Also mutual collision of particles cannot generate motion in the primordial matter.
- More over the random motion of the particles cannot generate circular motion in the primordial matter.
- Also angular velocity of rotary speed of the nebular cannot increase due to the increase in size of the nebular as assumed by Kant.
Big bang theory
This theory was proposed by Lemaitre Georges and Edwin Itubble in the 1920s.the big bang theory explains that about 15 billion years ago, a great explosion occurred. This explosion caused the expansion of universe expand. This explosion is known as the Big bang. At the time of this event all matter and energy in space were contained in one point. The expansion pushed matter and energy outward expanding in all direction, forming a collection of dust, gas and stars held to gather by gravitational attraction. Later the sun, gas and dust collided and aggregated into small grains, eventually forming larger bodies called planetesimals [very small planets]
Some of these small planets reached diameters of several hundred kilometers and later formed the current eight planets [mercury, Venus, earth, mars Jupiter, Saturn, Uranus and Neptune] and then satellites.
However scientists and institutions such as NASA [National aeronautics and space Administration] are still investigating to find out if there is existence of other planets in the outer space
Critiques of the theory
The critiques of the theory are that, it appears all galaxies emerged at the same time; therefore, they could potentially have at least the same age. However, but this has not been the case, in fact current astronomical researchers have found that while other galaxies are very old, there are many young galaxies around and far from the earth.
Inter- stellar dust hypothesis
In 1943, a Russian scientist Otto Schmidt proposed a theory known as inter-stellar dust hypothesis. It explains the complex problems of the origin and characteristics of the solar system and the earth. According to the inter- stellar dust hypothesis, the sun during its galactic revolution, captured the dark matter of the universe. The dark matter [inter stellar dusts] of gaseous cloud and dust particles had their own angular momentum. The dark matter after being attractive by the sun during its galactic revolution ”started revolving around the primitive rotating sun.
The intense heat from the sun dispersed the gaseous particles towards the margins of the disk.
Collision among the dust particles started the process of aggregation and accretion around the bigger particles which become the essentials of the future planets. With the passage of time, these embryos captured more and more matter and grew in size to become asteroids. Furthermore these asteroids grew in size due to continuous acceleration of nearby matter around them these become planets.
Critique
- The hypothesis has been criticized that gravitational force of the primitive sun was incapable of capturing dark matter scattered in the universe.
- Another critique is that some astrophysicists’ believe that meteorites and asteroids were formed from disintegration of planet .They reject the idea that the planets were formed out of meteorites and asteroids.
Position of the earth in the solar system
Earth is the third planet in the position from the sun. It is located about 150 millions km from the sun. And it is the only planet that supports life due to the presence of water.
It has an atmosphere which contains different gases essential for living things. Also the position of the earth in the solar system makes its temperature suitable for plants and animals.
The position of earth in the solar system
Challenges facing the planet earth
(a) Climate change
(b) Pollution
(c) Deforestation
(e) Loss of diversity and
(f) Overconsumption of natural resources
Shape and size of the earth.
The earth is the fifth largest planet in the solar system in terms of size and mass. Its shape is like flattened sphere known as an oblate spheroid (geoid).
The distance through the centre from the North Pole to the South Pole is approximately 12713kms where as the distance through the centre of the earth at equator is approximately 12757kms.
The circumference of the earth at the equator is about 40085kms while the polar circumference is 39955kms.
Evidence to show that the earth has an oblate spheroid shape(spherical shape of the earth)
There are some several evidences which are used to prove that the earth is sphere like structure, some of them are shown as follows
- sunrise and sunset
- circumnavigation of the earth
- aerial photographs
- ship’s visibility
- lunar eclipse
a]Sunrise and sunset
The sunrise and sunset at different places of the earth. People in the east see the sun earlier than the people in the west due to earth’s rotation from west to east. If the earth was flat the whole world would have sunrise and sunset at the same time.
b] Circumnavigation of the earth
If traveling from a certain point of the earth and you go straight around the earth you will come to the point of origin. The first traveler around the world named Magellan in 1519-1522 proved this.
c] Aerial photographs
Photographs taken by satellites or aeroplane from the air show that the earth has a curved or round shape.
d] Ship’s visibility
If you are in the coast viewing a ship which is very far you will see the soot, then the pipe and eventually the whole ship gradually appears. If the earth were flat the ship would have been seen all at once
spherical earth
flat earth
e] Lunar eclipse
The shadow of the earth thrown to the moon during lunar eclipse is always round. Only a spherical object can give a circular shadow.