Origin / Evolution of Earth
Nebular theory of Laplace
The earth evolved 4.6 billion years ago. Earlier it was in a gaseous form which was consisted of Hydrogen and Helium.
It was a nebula and was rotating at a high speed. Because of its high speed, the energy of hydrogen and helium led to a radiation process that resulted in the loss of heat and condensation.
During that process, it contracted and compressed. Gradually that gas converted into a solid form. But before turning into solid form a ring was separated from it and that led to the formation of the nine planets.
During that process, the heavier elements collected near the core of the Earth and lighter elements remained at the surface of the Earth.
Hence if you move from the surface to the core of the earth, the density increases with the depth.
On the basis of this theory, studies were conducted to study the density, temperature and structure of the Earth.
These studies also provided evidence in the support of this theory.
Evolution of Lithosphere
The lithosphere is a solid continental crust or land. The earth was volatile during its primordial stage. The gradual increase in the density led to the increase in temperature inside. As a result, the material inside separated on the basis of their densities. The heavier materials accumulated in the center and the lighter ones moved toward the surface.
Later, it cooled further and solidified and condensed into a smaller size, it resulted in the development of the outer surface in the form of a crust.
Evolution of Atmosphere
Nitrogen and oxygen contributed to the composition of the Earth’s present atmosphere.
The atmosphere has evolved into three stages, first, by loss of primordial atmosphere. Second, the hot interior of the earth contributed to the evolution of the atmosphere. Third, it was modified by the living organism through the process of photosynthesis.
During the cooling of the earth, gases and water vapor were released from the earth and this led to the evolution of the present atmosphere.
The early atmosphere largely contained water vapor, nitrogen, carbon dioxide, methane, ammonia and free oxygen.
The volcanic eruptions contributed to release of water vapor and gases into the atmosphere. The outpour of gases from the interior of the earth is called degassing.
The Earth’s Movement
Earth’s Rotation
The Earth rotates on its own axis from west to east and hence we feel that the Sun rises in the east. The rotation of the earth takes 24 hours to complete its 360 degrees rotation, causing day and night.
Earth rotates 15 degrees longitude in 1 hour. If we move to the eastern parts of the Earth, we gain a day and if we move to the western side of the Earth, we lose a day.
Earth’s Revolution
The Earth revolves around the Sun in an elliptical orbit at a speed of 18.5 miles per second. One complete revolution around the sun takes one year, causing the seasons and the year.
Day and Night And Seasons on Earth
The earth is spherical in shape, causing variations in receiving the Sun rays and day and night. Aristotle was the first pioneer who stated that the earth is spherical.
The earth is tilted by 23.5 degrees on its axis and revolves around the Sun in an elliptical path. And that revolution of the earth creates variations of seasons and the year.
A year is usually divided into summer, winter, spring, and autumn seasons. And these changes in season happen due to the change in the position of the earth around the sun.
On 21st June, the northern hemisphere is tilted towards the sun. The rays of the Sun fall directly on the tropic of cancer, as a result, these areas receive more heat and the areas near the poles receive less heat as the rays of the sun are slanting. The North pole is inclined towards the sun and the places beyond the arctic circle experience continuous daylight for about six months. And most of the regions in the northern hemisphere experience the summer season. The longest day and the shortest night at these places occur on 21st June.
At the same time in the southern hemisphere, all these conditions are reversed. And this region experiences the winter season. The nights are longer than the days. This position of the earth is called Summer Solstice.
On 22nd December, the tropic of Capricorn receives direct sun rays of the sun as the south pole tilts toward it. As the sun’s rays fall vertically at the tropic of Capricorn, a larger region of the southern hemisphere gets light. Therefore, it is summer in the southern hemisphere with longer days and shorter nights. The reverse happens in the northern hemisphere. This position of the earth is called the winter solstice.
On the 21st march and 23rd September, direct rays of the sun fall on the equator. As a result, the whole earth experiences equal days and equal nights. This is called an equinox.
On 23rd September, it is autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere. The opposite is the case on 21st March, when it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere.
Latitudes
These are imaginary horizontal lines on earth. Latitudes are the angular distance of a place from the equator. Latitudes are concentric circles and are also called parallels.
Some of the prominent latitudes are the equator, tropic of cancer, tropic of Capricorn, arctic circle and Antarctic circle.
Longitudes
These are imaginary vertical lines. Longitudes are the angular distance of a place from the Prime meridian or Greenwich Meridian. It runs through Greenwich, UK and hence it is called the Greenwich meridian.
The prime meridian or Greenwich meridian is a ‘0’ degree reference longitude that divides the globe into the eastern and western hemispheres.
The prime meridian runs through the international Greenwich observatory.
And opposite to it, 180 degrees longitude is called an antimeridian which is the basis for the International Date Line.
International date line
The 180 degrees longitude is referred as International Date Line. And this is exactly opposite to the prime meridian.
Why International Date Line OR that longitude is in a zig-zag shape?
When a person crosses the international date line, that person must change the date to avoid confusion.
The day starts from the western side of the line and ends at the east of the line. There are numerous small islands located in this region. And to avoid confusion about the dates and time the geographers decided the International Date Line must pass through the water body. Hence that line is zig-zag in shape. Moreover, if you move to the western side of the line, you lose 1 day and if you move to the eastern side of the line you gain 1 day.
Standard time
Every country selects its standard meridian. It is the angular distance between the standard meridian of a nation to Greenwich Meridian Time (GMT). On the basis of geographical extent, nations are free to select one or more time zones. For instance, India has single time zone on the other hand Russia has multiple time zones.
Chaibagaan time zone
Earlier during British rule in India, the British had launched chaibagaan time ( 1 hour ahead of IST) 150 years ago in Assam, especially for the tea planters.
India adopted a single time zone called Indian Standard Time (IST) after its Independence.
Again in 2000, these states demanded the chaibagaan time zone. In 2007, after a study by the Department of Science and Technology, the idea was rejected on the basis of administrative challenges.