Several theories have been put forward to explain the possible origins of the earth. The most prominent of these theories in relation to the formation of the earth include among others: Thales theory, Kant's theory, the big - bang theory, and the Biblical theory.

The biblical theory

This theory according to the book of Genesis asserts that, the earth was created by God alongside the "heaven" (Universe). However, modern scientists disagree with this theory. The scientists base their argument on rock dating. According to these scientists the earth is estimated to be at least between 3.5 and 4.5 billion years old. Yet according to the biblical theory, the universe is estimated to be about 6000 years, which is a great underestimation.

The big- bang theory

The Big-bang theory was put forward at the beginning of the 20th Century (1927) by a Belgian astronomer called Lemaitre Georges, and an American Scientist called Hubble Edwin. These two men assert that right from the beginning there was nothing. They asserted that, out of nothingness a big explosion, or big - bang took place. They asserted that from this explosion a speck of matter came in to existence. This primordial matter has since been expanding and as it expands, the universe and everything in it including the earth came into existence. This explosion is estimated to have occurred some 15,000,000,000 years ago. However, the only doubtable fact about the big-bang theory is how "Nothing " can explode to form the universe and the earth inclusive and how it appears today.

Thale's theory

According to Thale, water was the source of the earth. Thale arrived at his point after observing deposition along the Nile Delta, While Thale was within the Nile Delta, he observed that deposition of silt at the delta ied to outward growth of the delta and this led him to such a conclusion. The period is estimated to be between 624 - 565 B.C. However, this theory was short of mentioning the source of silt as he observed it and which led to delta growth. This could not qualify Thale's emphasis that water was the source of the Earth and everything in it.

Kant's theory

Kant postulated his theory in 1755 A.D. He asserted that, all the planets the earth inclusive, were formed from a series of rings of hot gases which progressively detached themselves from a mass of hot gas (probably the sun). According to Kant, each of these rings moved away and gradually condensed to form a planet, with the sun at the centre, and as a source of heat. Kant's has remained the most acceptable theory, because it offers the most satisfactory possible explanation as regards the possible origin of the earth. Kant's theory was later on supported and improved upon by Laplace in 1796.

The Shape of the Earth.

The earth is a sphere. It slightly bulges at the Equator, but is nearly flattened at the poles. It measures 40,085 km around the Equator, and only 39995 km at the poles. This has been proved so through the use of rockets and satellites within the atmosphere. Otherwise before, and for along time, the earth was regarded to be flat.

Figure 11: A globe is the most accurate way to represent Earth's curved surface.

(Source:http://upload.wikimedia.org/ wikipedia/commons/ thumb/9/9f/GEO_Globe.jpg/ 519px-GEO_Globe.jpg,

License: GNU-FDL)

The first person to prove that the earth is not flat was Pythagoras in about 530 B.C. Later at about 276 B.C. Eratosthenes devised means of estimating the size of the earth. Today other various proofs have been put in place to suggest the nature and shape of the earth. For example'

The altitude (height) of the polar star which varies with latitude. All the planets in the solar system are round, so is the earth. The rising sun is seen first in the eastern countries, and later on in the western countries. This could be understood using Newton's law of gravitation where all particles making up the earth are being pulled towards the centre of the earth. The scientists at first assumed that the earth is round perhaps because of the following reasons:

Using Magellan's Voyage. Magellan sailed from Seville in Spain in 1519 A.D. and the voyage was completed at the same point (Seville) three years later in 1522 A.D. Using Eratosthene's (276 - 196 B.C) theory that is, he devised a method for estimating the size of the earth. He calculated the circumference of the earth and found it to be 252,000 stadia. Using Pythagoras (530 B.C) theory where he observed that, the approaching ship from beyond the horizon, the mast of the ship appear first, then followed by the sail and last comes the hull. He therefore, observed that, the surfaces of the sea was not flat, but curved.