Earth and its Geological time scale:-
Origin of the Earth:-
EARLY THEORIES:-
A large number of hypotheses were put forth by different philosophers and scientists regarding the origin of the earth. One of the earlier and popular arguments was by German philosopher Immanuel Kant. Mathematician Laplace revised it in 1796. It is known as Nebular Hypothesis. The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating. Later in 1900, hamberlain and Moulton considered that a wandering star approached the sun. As a result, a cigar-shaped extension of material was separated from the solar surface. As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed into planets. Sir James Jeans and later Sir Harold Jeffrey supported this argument. At a later date, the arguments considered of a companion to the sun to have been coexisting. These arguments are called binary theories. In 1950, Otto Schmidt in Russia and Carl Weizascar in Germany somewhat revised the ‘nebular hypothesis’, though differing in details. They considered that the sun was surrounded by solar nebula containing mostly the hydrogen and helium along with what may be termed as dust. The friction and collision of particles led to formation of a disk-shaped cloud and the planets were formed through the process of accretion. However, scientists in later period took up the problems of origin of universe rather than that of just the earth or the planets.
MODERN THEORIES:-
Origin of the Universe:-
The most popular argument regarding the origin of the universe is the Big Bang Theory. It is also called expanding universe hypothesis. Edwin Hubble, in 1920, provided evidence that the universe is expanding. As time passes, galaxies move further and further apart. You can experiment and find what does the expanding universe mean. Take a balloon and mark some points on it to represent the galaxies. Now, if you start inflating the balloon, the points marked on the balloon will appear to be moving away from each other as the balloon expands. Similarly, the distance between the galaxies is also found to be increasing and thereby, the universe is considered to be expanding. However, you will find that besides the increase in the distances between the points on the balloon, the points themselves are expanding. This is not in accordance with the fact. Scientists believe that though the space between the galaxies is increasing, observations do not support the expansion of galaxies. So, the balloon example is only partially correct.
The Big Bang Theory considers the following stages in the development of the universe.
(i) In the beginning, all matter forming the universe existed in one place in the form of a “tiny ball” (singular atom) with an unimaginably small volume, infinite temperature and infinite density.
(ii) At the Big Bang the “tiny ball” exploded violently. This led to a huge expansion. It is now generally accepted that the event of big bang took place 13.7 billion years before the present. The expansion continues even to the present day. As it grew, some energy was converted into matter. There was particularly rapid expansion within FRACTIONS of a second after the bang. Thereafter, the expansion has slowed down. Within first three minutes from the Big Bang event, the first atom began to form.
(iii) Within 300,000 years from the Big Bang, temperature dropped to 4,500 K (Kelvin) and gave rise to atomic matter. The universe became transparent.
The expansion of universe means increase in space between the galaxies. An alternative to this was Hoyle’s concept of steady state. It considered the universe to be roughly the same at any point of time. However, with greater evidence becoming available about the expanding universe, scientific community at present favours argument of expanding universe.
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 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 structure. 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.
Evolution of Lithosphere:-
The earth was mostly in a volatile state during its primordial stage. Due to 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 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 earth’s atmosphere is chiefly contributed by nitrogen and Oxygen. There are three stages in the evolution of the present atmosphere. The first stage is marked by the loss of primordial atmosphere. In the second stage, the hot Interior Of The Earth contributed to the evolution of the atmosphere. Finally, 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 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. Continuous volcanic eruptions contributed water vapour and gases.to the atmosphere. 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. This tells us that the oceans are as old as 4,000 million years. Sometime 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 initially the earth 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 much older than some 3,000 million years. It can be assumed that life began to evolve sometime 3,800 million years ago.
INTERIOR OF THE EARTH:-
SOURCES OF INFORMATION ABOUT THE INTERIOR:-
The earth’s radius is 6,370 km. No one can reach the centre of the earth and make observations or collect samples of the material. Under such conditions, you may wonder how scientists tell us about the earth’s interior and the type of materials that exist at such depths. 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.
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 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.
Analysis of Properties of matter indirectly provides information about the interior. We know 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. The details of these characteristics with reference to each layer of the interior are discussed later in this chapter. Another source of information are 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.
The other indirect sources include Gravitation, Magnetic Field, and seismic activity. 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. The gravity values also differ according to the mass of material. The uneven distribution of mass of material within the earth influences this value. The reading of the gravity at different places is influenced by many other factors. These readings differ from the expected values. Such a difference is called gravity anomaly. Gravity anomalies give us information about the distribution of mass of the material in the crust of the earth. 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.,
The history of the Earth is divided into four eons: the Hadean, Archean, Proterozoic, and Phanerozoic. The Hadean eon lasted from the formation of the Earth about 4.54 billion years ago to about 4 billion years ago. It was a time of great upheaval, as the Earth was still cooling and solidifying. The Archean eon lasted from about 4 billion years ago to about 2.5 billion years ago. During this time, the Earth’s atmosphere and oceans began to form, and life first appeared. The Proterozoic eon lasted from about 2.5 billion years ago to about 540 million years ago. During this time, life on Earth began to diversify, and the first multicellular organisms appeared. The Phanerozoic eon is the current eon, and it began about 540 million years ago. It is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic.
The Paleozoic era lasted from about 540 million years ago to about 252 million years ago. During this time, the first land animals appeared, and the first forests formed. The Mesozoic era lasted from about 252 million years ago to about 66 million years ago. During this time, the dinosaurs ruled the Earth. The Cenozoic era is the current era, and it began about 66 million years ago. During this time, the dinosaurs went extinct, and mammals became the dominant land animals.
The Cambrian period was the first period of the Paleozoic era. It lasted from about 540 million years ago to about 485 million years ago. During this time, the first animals with hard skeletons appeared. The Ordovician period was the second period of the Paleozoic era. It lasted from about 485 million years ago to about 443 million years ago. During this time, the first fish appeared. The Silurian period was the third period of the Paleozoic era. It lasted from about 443 million years ago to about 416 million years ago. During this time, the first land Plants appeared. The Devonian period was the fourth period of the Paleozoic era. It lasted from about 416 million years ago to about 359 million years ago. During this time, the first amphibians appeared.
The Carboniferous period was the fifth period of the Paleozoic era. It lasted from about 359 million years ago to about 299 million years ago. During this time, the first forests formed. The Permian period was the sixth period of the Paleozoic era. It lasted from about 299 million years ago to about 252 million years ago. During this time, the first reptiles appeared.
The Triassic period was the first period of the Mesozoic era. It lasted from about 252 million years ago to about 201 million years ago. During this time, the dinosaurs first appeared. The Jurassic period was the second period of the Mesozoic era. It lasted from about 201 million years ago to about 145 million years ago. During this time, the dinosaurs reached their peak. The Cretaceous period was the third period of the Mesozoic era. It lasted from about 145 million years ago to about 66 million years ago. During this time, the dinosaurs went extinct.
The Paleogene era was the first era of the Cenozoic era. It lasted from about 66 million years ago to about 23 million years ago. During this time, the first mammals began to evolve into the forms we see today. The Neogene era was the second era of the Cenozoic era. It lasted from about 23 million years ago to about 2.6 million years ago. During this time, the first primates appeared. The Quaternary period is the current period of the Cenozoic era. It began about 2.6 million years ago. During this time, the first humans appeared.
The Earth is a dynamic planet with a long and complex history. The four eons and three eras of the Earth’s history are each marked by significant events and changes. The Earth’s atmosphere, oceans, and life have all evolved over time, and the planet continues to change today.
Here are some frequently asked questions and short answers about the following topics:
The universe
What is the universe?
The universe is everything that exists, from the smallest subatomic particles to the largest galaxies. It includes all of space and time, and its contents are constantly interacting with each other.How big is the universe?
The universe is so big that it is impossible to measure its size with any certainty. However, scientists estimate that it is at least 93 billion Light-years across.How old is the universe?
The universe is about 13.8 billion years old. This is the age of the oldest light that we can see, which comes from the cosmic microwave background radiation.What is the fate of the universe?
The fate of the universe depends on its density. If the density of the universe is high enough, gravity will eventually cause all of the matter in the universe to collapse back in on itself in a “big crunch.” If the density of the universe is low enough, the universe will continue to expand forever.What is The Solar System?
The solar system is the system of planets and other objects that orbit the Sun. It includes the Sun, eight planets, five dwarf planets, and millions of asteroids, comets, and meteoroids.What are the planets in the solar system?
The planets in the solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Mercury is the closest planet to the Sun, and Neptune is the farthest.What are the dwarf planets in the solar system?
The dwarf planets in the solar system are Pluto, Eris, Makemake, and Haumea. Pluto was originally classified as a planet, but it was reclassified as a dwarf planet in 2006.What are the moons in the solar system?
The solar system has over 200 moons. The largest moon in the solar system is Ganymede, which is a moon of Jupiter.The Earth
What is the Earth?
The Earth is the third planet from the Sun and the only planet in the solar system known to support life. It is a terrestrial planet with a solid surface, a thick atmosphere, and liquid water.What is the composition of the Earth?
The Earth is made up of four main layers: the crust, the mantle, the outer core, and the inner core. The crust is the outermost layer and is made up of solid rock. The mantle is the next layer down and is made up of molten rock. The outer core is the next layer down and is made up of liquid iron. The inner core is the innermost layer and is made up of solid iron.What is the atmosphere of the Earth?
The Earth’s atmosphere is made up of several gases, including nitrogen, oxygen, argon, carbon dioxide, and water vapor. The atmosphere protects the Earth from harmful radiation from the Sun and helps to regulate the Earth’s temperature.What is the Climate of the Earth?
The Earth’s climate is the Average weather conditions over a long period of time. The Earth’s climate is constantly changing, and it has been affected by many factors, including the Earth’s orbit around the Sun, the Earth’s tilt, and the Earth’s atmosphere.Life on Earth
What is life?
Life is a complex system that is capable of self-replication and self-maintenance. Life is found on Earth in many different forms, including plants, animals, and Microorganisms.How did life on Earth begin?
The origin of life on Earth is a mystery that scientists are still trying to solve. There are many theories about how life began, but there is no one definitive answer.What are the different types of life on Earth?
There are many different types of life on Earth, including plants, animals, and microorganisms. Plants are photosynthetic organisms that use sunlight to produce food. Animals are heterotrophic organisms that eat plants or other animals for food. Microorganisms are tiny organisms that can be found in all parts of the Earth, including the air, water, Soil, and even inside other organisms.What is the future of life on Earth?
The future of life on Earth is uncertain. The Earth’s climate is changing, and this change is having a negative impact on many species of plants and animals. It is possible that some species will become extinct, and it is also possible that new species will evolve.
Sure, here are some multiple choice questions about the Earth and its geological time scale:
The Earth is about how old?
(A) 4.543 billion years old
(B) 4.543 million years old
(C) 4.543 thousand years old
(D) 4.543 years oldThe Earth’s geological time scale is divided into how many eons?
(A) 4
(B) 3
(C) 2
(D) 1The Phanerozoic eon is the most recent eon in the Earth’s geological time scale. It is divided into how many eras?
(A) 3
(B) 4
(C) 5
(D) 6The Mesozoic era is the era that includes the age of dinosaurs. It lasted for how long?
(A) 252 million years
(B) 186 million years
(C) 160 million years
(D) 66 million yearsThe Cenozoic era is the era that we are currently living in. It began how long ago?
(A) 66 million years ago
(B) 252 million years ago
(C) 541 million years ago
(D) 4.543 billion years agoThe Quaternary period is the most recent period in the Cenozoic era. It is divided into how many epochs?
(A) 2
(B) 3
(C) 4
(D) 5The Holocene epoch is the epoch that we are currently living in. It began how long ago?
(A) 11,700 years ago
(B) 12,900 years ago
(C) 13,000 years ago
(D) 14,700 years agoThe Pleistocene epoch is the epoch that preceded the Holocene epoch. It lasted for how long?
(A) 2.6 million years
(B) 1.8 million years
(C) 1.6 million years
(D) 1.2 million yearsThe last glacial period was a period of time when Glaciers covered much of the Earth’s surface. It ended how long ago?
(A) 11,700 years ago
(B) 12,900 years ago
(C) 13,000 years ago
(D) 14,700 years agoThe Earth’s climate is currently in a period of warming. This warming trend is known as what?
(A) Global Warming
(B) Climate Change
(C) The Greenhouse Effect
(D) The ozone hole