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ORIGIN OF THE EARTH
Various scientists and philosophers have propounded from time to time their concepts, hypotheses and theories to unravel the mystery and to solve the riddle of the problems of the origin and evolution of our solar system in general and of the earth in particular but none of these could be accepted by the majority of the scientific community.
Though there is no common consensus among scientists about the origin of our solar system it can be safely argued that all planets of our solar system are believed to have been formed by the same process.
It means that all the concepts, hypotheses and theories propounded for the origin of the solar system are also applicable for the origin of the earth.
SCIENTIFIC CONCEPTS
The scientific concepts, generally based on sound principles of hard sciences, are usually divided into two schools e.g.
- ’hot origin concepts’
- ‘Cold origin concepts’.
HOT ORIGIN CONCEPTS
According to the school of ‘hot origin’, our solar system and therefore the earth is believed to have been formed from the matter which as either initially
hot or was heated up in the process of the origin of the earth.
COLD ORIGIN CONCEPTS
On the other hand, according to the school of ‘cold origin,’ our solar system together with the earth was formed of matter which was either initially cold or always remained cold.
After the formation, the earth was formed of matter which was either initially cold or always remained cold.
After the formation, the earth might have been heated up due to the presence of radioactive elements or only the interior of the earth might have been heated up due to intense pressure exerted by the superincumbent load of the upper layers.
CLASSIFICATION OF SCIENTIFIC CONCEPTS
On the basis of the number of heavenly bodies involved in the origin of the solar system and the earth the scientific concepts are further divided into three groups.
(i) Monistic concept (involving only one heavenly body,
(ii) Dualistic concept (involving two heavenly bodies) and
(iii) Binary star concept or trihybrid concept (involving more than two heavenly bodies).
BIG BANG THEORY
The Big Bang Theory postulated in the 1950s-1960s and validated in 1972 through convincing evidence received from COBE (Cosmic Background Explorer) explains the origin of the universe and everything in it including ourselves on the premise that the universe contained many millions of galaxies, each on ‘having thousands of millions of stars and each star having numerous planets around them’.
According to this theory, everything in the universe emerged from a point known as the singularity, 15 billion years ago.
The galaxies moved apart from one another as the empty space between them expanded.
In the beginning, the universe was much smaller as there was less space between the galaxies.
All of the matter in the universe was created in one instant at a fixed moment in time.
“As the universe expanded for 15 billion years, the hot radiation in the original fireball also expanded with it, and cooled as a result.”
It may be summarized that there was a single fireball some 15 billion years ago.
‘There were already wispy clouds of matter stretching across vast distances, upwards 500 million light years across.
As those clouds collapsed in upon themselves, pulled together by their own gravity, they would have broken up and formed clusters of galaxies with the galaxies themselves breaking up into stars like those of the Milky Way’.
The stars might have broken up to form their planets as our earth.
STAGES IN THE EVOLUTION OF THE EARTH
C.Chamberlin has attempted to describe and explain the evolution of different components of the earth. e.g. continents and ocean basins, folds and faults, volcanoes and earthquakes, mountains and plains, heat of the interior of the earth and its structure and the origin and evolution of its atmosphere through specific periods or stages.
FIRST STAGE – ‘the period of planetesimal accession’ or ‘the period of acquisition of the present shape and size by the earth’.
SECOND STAGE – “the period of dominant volcanism” or ‘the period of the evolution of the earth’s interior and the evolution of continents and ocean basins.
THIRD STAGE – ‘the actual geological period’ or ‘the period of the formation of the folds and faults, mountains and plateau etc.
These stages of the evolution of the earth are separated from each other only for the sake of convenience; otherwise, these are so interlinked with each other that it is quite difficult to differentiate one stage from the other.
EVOLUTION OF THE EARTH
The planet earth initially was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. This is far from the present-day picture of the earth.
Hence, there must have been some events–processes, which may have caused this change from rocky, barren and hot earth to a beautiful planet with ample amount of water and a conducive atmosphere favouring the existence of life.
Between the 4,600 million years and the present, led to the evolution of life on the surface of the planet.
The earth has a layered
From the outermost end of the atmosphere to the centre of the earth, the material that exists is not uniform. The atmospheric matter has the least density
From the surface to deeper depths, the earth’s interior has different zones and each of these contains materials with different characteristics.
DEVELOPMENT OF LITHOSPHERE
The earth was mostly in a volatile state during its primordial stage.
Due to a gradual increase in density the temperature inside has increased.
As a result, the material inside started getting separated depending on their densities.
This allowed heavier materials (like iron) to sink towards the centre of the earth and the lighter ones to move towards the surface.
With the passage of time, it cooled further and solidified and condensed into a smaller size.
This later led to the development of the outer surface in the form of a crust.
During the formation of the moon, due to the giant impact, the earth was further heated up.
It is through the process of differentiation that the earth forming material got separated into different layers.
Starting from the surface to the central parts, we have layers like the crust, mantle, outer core and inner core.
From the crust to the core, the density of the material increases.
EVOLUTION OF ATMOSPHERE AND HYDROSPHERE
The present composition of the earth’s atmosphere is chiefly contributed by nitrogen and oxygen.
There are three stages in the evolution of the present atmosphere.
FIRST STAGE – This marked by the loss of primordial atmosphere.
SECOND STAGE – the hot interior of the earth contributed to the evolution of the atmosphere
THIRD STAGE- the composition of the atmosphere was modified by the living world through the process of photosynthesis.
The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds.
This happened not only in the case of the earth but also in all the terrestrial planets, which were supposed to have lost their primordial atmosphere through the impact of solar winds.
During the cooling of the earth, gases and water vapour were released from the interior solid earth. This started the evolution of the present atmosphere.
The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen
The process through which the gases were outpoured from the interior is called degassing.
As the earth cooled, the water vapour released started getting condensed.
The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains
The rainwater falling onto the surface got collected in the depressions to give rise to oceans.
The earth’s oceans were formed within 500 million years from the formation of the earth.
The oceans are as old as 4,000 million years and around 3,800 million years ago, life began to evolve.
However, around 2,500-3,000 million years before the present, the process of photosynthesis got evolved. Life was confined to the oceans for a long time.
Oceans began to have the contribution of oxygen through the process of photosynthesis.
Eventually, oceans were saturated with oxygen, and 2,000 million years ago, oxygen began to flood the atmosphere.
ORIGIN OF LIFE
The last phase in the evolution of the earth relates to the origin and evolution of life
It is undoubtedly clear that the initial or even the atmosphere of the earth was not conducive for the development of life
Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them.
This assemblage was such that they could duplicate themselves converting inanimate matter into living substance.
The record of life that existed on this planet in different periods is found in rocks in the form of fossils.
The microscopic structures closely related to the present form of blue algae have been found in geological formations that are much older than these were some 3,000 million years ago.
It can be assumed that life began to evolve sometime 3,800 million years ago.
INTERIOR OF THE EARTH
INTRODUCTION
The configuration of the surface of the earth is largely a product of the processes operating in the interior of the earth.
Exogenic as well as endogenic processes are constantly shaping the landscape.
A proper understanding of the physiographic character of a region remains incomplete if the effects of endogenic processes are ignored.
Human life is largely influenced by the physiography of the region.
Therefore, it is necessary that one gets acquainted with the forces that influence landscape development.
ENDOGENIC PROCESSES
The energy emanating from within the earth is the main force behind endogenic geomorphic processes. This energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth.
EXOGENIC PROCESSES
The exogenic processes derive their energy from atmosphere determined by the ultimate energy from the sun and also the gradients created by tectonic factors.
SOURCES OF INFORMATION ABOUT THE INTERIOR
The earth’s radius is 6,370 km.
Most of our knowledge about the interior of the earth is largely based on estimates and inferences.
Yet, a part of the information is obtained through direct observations and analysis of materials.
DIRECT SOURCES
The most easily available solid earth material is surface rock or the rocks we get from mining areas.
Gold mines in South Africa are as deep as 3 – 4 km. going beyond this depth is not possible as it is very hot at this depth.
Besides mining, scientists have taken up a number of projects to penetrate deeper depths to explore the conditions in the crustal portions.
Scientists world over are working on two major projects such as “Deep Ocean Drilling Project” and “Integrated Ocean Drilling Project”.
The deepest drill at Kola, in the Arctic Ocean, has so far reached a depth of 12 km.
This and many deep drilling projects have provided large volume of information through the analysis of materials collected at different depths.
Volcanic eruption forms another source of obtaining direct information.
As and when the molten material (magma) is thrown onto the surface of the earth, during volcanic eruption it becomes available for laboratory analysis.
However, it is difficult to ascertain the depth of the source of such magma.
INDIRECT SOURCES OF EARTH’S INTERIOR
Analysis of properties of matter indirectly provides information about the interior.
Through the mining activity that temperature and pressure increase with the increasing distance from the surface towards the interior in deeper depths.
Moreover, it is also known that the density of the material also increases with depth.
It is possible to find the rate of change of these characteristics
Knowing the total thickness of the earth, scientists have estimated the values of temperature, pressure and the density of materials at different depths.
METEORS
Another source of information is the meteors that at times reach the earth.
However, it may be noted that the material that becomes available for analysis from meteors, is not from the interior of the earth.
The material and the structure observed in the meteors are similar to that of the earth.
They are solid bodies developed out of materials same as, or similar to, our planet.
Hence, this becomes yet another source of information about the interior of the earth.
GRAVITATION
The gravitation force (g) is not the same at different latitudes on the surface. It is greater near the poles and less at the equator.
This is because of the distance from the centre at the equator being greater than that at the poles.
GRAVITY ANOMALY
The gravity values also differ according to the mass of the material.
The uneven distribution of mass of material within the earth influences this value.
The reading of gravity at different places is influenced by many other factors.
These readings differ from the expected values. Such a difference is called a gravity anomaly.
Gravity anomalies give us information about the distribution of mass of the material in the crust of the earth.
OTHER INDIRECT SOURCES
Magnetic surveys also provide information about the distribution of magnetic materials in the crustal portion, and thus, provide information about the distribution of materials in this part.
Seismic activity is one of the most important sources of information about the interior of the earth.
