THE ORIGIN AND EVOLUTION OF THE EARTH

 THE ORIGIN AND EVOLUTION

OF THE EARTH

 Early  Theories origin of the Earth

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 NebularHypotñesis. 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, Chamberlain 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. arguments. 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 EORIEO origin of the Universe

The most popular argument regarding the origin of the universe is the Big Bring Theos. 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 startiriflating 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  Cmd that besides the increase in the distances between the points on the

Big bang theory:

It is also called the expanding universe hypothesis.
In 1920, Edwin Hubble provides evidence that the universe is expanding.
Over time, the distance between Galaxies is increasing.

As per big bang theory:

• All matter that formed universe was existed in one place having less than the area of the atom with unimaginable small volume, infinite temperature, and infinite density.
• It exploded with a big bang around 13.7 billion years ago.
• Within 3 minutes from the big bang event, the first atom was formed.
• Over time, the energy was converted into matter.
• After the formation of atomic matters, around 3 lakh years from the big bang, the universe becomes transparent.

Star formation as per big bang theory:

• It starts at 5 billion years ago.
• The early universe, distribution of matter and energy was not even. Due to the initial density difference, it gets rises to gravitational forces. As a result, the matter came together.
• The universe is a collection of large number galaxies.
• Galaxy: contains a large number of stars.
• The formation of galaxies started from the nebula that is made up of hydrogen and helium gases.

Formation of planets:

The following are stages in the development of planets:

First stage:

• The star is lumps of gas within nebula. The gravitational force within lumps leads to the formation of core and the huge rotating discs of gases and dust around the gaseous core.

Second stage:

• The matters around the core, getting condensed into smaller rounded objects. Planetesimals are a large number of smaller bodies and by collision, larger bodies start forming.

Final stage:

• These planetesimals form and form larger planet bodies.

Our solar system:

Our solar system formed 5 billion years ago. The solar system is comprised of nine planets, many satellites, asteroids, and one sun.
Nine planets are in two types:

• Inner planet or terrestrial or Earth-like planet:
• These are Mercury, Venus, Earth, Mars
• Outer planet or Julian or giant planets:
• These are Jupiter, Saturn, Uranus,  Neptune, and Pluto

Jovian planet is larger in size as compared to the terrestrial planet and has a thick atmosphere mostly made of helium and hydrogen.

Difference between Julian and Terrestrial planets:

• Terrestrial planets are formed by solid particles whereas Julian is formed by gaseous particles.
• Solar winds blew off lots of gases and dust from terrestrial planets where similar removal has not happened in Jovian planets.
• A terrestrial planet is smaller hence lower gravity could not hold the escaping gases.

Evolution of earth:

• Initially, the earth was a barren, rocky, and hot object with a thin atmosphere of hydrogen and helium.
• Earth has a layered structure from the outmost atmosphere to central of earth. It is not uniform.

Development of lithosphere:
Due to the gradual increase in density, the temperature inside the earth is increasing. As a result, material getting separated depending on their density. Iron sink towards the center and lighter one move towards the surface.
During the formation of the moon, the earth was further heated up. Further, the process of differential, three major layers made on earth.
These three layers are:

• Crust
• Mantle
• Core

Evolution of atmosphere and hydrosphere:

The present atmosphere made by three stages:
First stages:

• Loss of primordial atmospheres such as helium and hydrogen blew off by solar winds.

Second stage:

• The hot interior of earth contributed to the evolution of the atmosphere. During the cooling, gases and water vapor from the interior of the earth came out to the atmosphere. At this stage, the atmosphere is largely comprised of water vapor, nitrogen, carbon dioxide, methane, ammonia, and very little of free oxygen. This process is called degassing.

Third stage:

• The composition of the atmosphere was modified by living organisms through photosynthesis and oxygen began to flood the atmosphere.
• Carbon dioxide in the atmosphere got dissolved in rainwater and further decrease causing more condensation and more land.

Origin of life:

• Origin of life is a kind of chemical reaction. First, it generated complex organic molecules that could duplicate themselves converting into living substance. Life began to evolve, 3800 million years ago from blue algae.

1. How did Earth and other planets form? 

The Solar System is composed of a set of radically different types of planets and moons— from the gas giants Jupiter, Saturn, Uranus, and Neptune to the rocky inner planets. Centuries of studying Earth, its neighboring planets, and meteorites have enabled the development of models of the birth of the Solar System. Astronomical observations from increasingly powerful telescopes have added a new dimension to these models, as have studies of asteroids, comets, and other planets via spacecraft, as well as geochemical studies of stardust and meteorites. While it is generally agreed that the Sun and planets all coalesced out of the same nebular cloud, little is known about how Earth obtained its particular chemical composition, or why the other planets ended up so different from Earth and from each other. For example, why has Earth, unlike every other planet, retained the unique properties—such as the presence of water—that allow it to support life? New measurements of Solar System bodies and extrasolar planets and objects, will further advance understanding of the origin of Earth and the Solar System. NASA/NDGC

 2. What happened during Earth’s “dark age” (the first 500 million years)?

 It is now believed that during Earth’s formation, a Mars-sized planet collided with it, creating a huge cloud of debris that became Earth’s Moon and releasing so much heat that the entire planet melted. But little is known about how the resulting molten rock evolved during the planet’s infancy into the Earth we know today. The first 500 million years of Earth’s existence, known as the Hadean Eon, is a critical missing link in understanding how the planet’s atmosphere, oceans, and differentiated layers of core, mantle, and outer crust developed. Scientists have almost no idea how fast the surface environment evolved, how the transition took place, or when conditions became hospitable enough to support life. Some clues from Earth’s oldest minerals (zircons), as well as from Earth’s Moon and other planets are allowing a clearer picture of the Hadean Eon to gradually emerge. The future is certain to provide additional breakthroughs. The amount of information that can be extracted from even the tiniest samples of old rocks and minerals is increasing rapidly, and with concerted effort, it is expected that many more ancient rocks and mineral samples will be found.

 

3. How did life begin?

 In The Origin of Species, Charles Darwin (1859) hypothesized that new species arise by the modification of existing ones—that the raw material of life is life. But somehow and somewhere, the tree of life had to take root from nonliving precursors. When, where, and in what form did life first appear? The origin of life is one of the most intriguing, difficult, and enduring questions in science. Scientists have toiled to create life from sparks and gasses in the laboratory to illuminate how life first formed in Earth’s early conditions. But even pinning down what those early conditions were remains an elusive goal. From what materials did life originate? Did life, as Darwin speculated, originate in a “warm little pond,” perhaps a tidal pool repeatedly dried and refreshed? Or might life be rooted among hydrothermal vents? Could life’s origins even lie beyond Earth? Developing an accurate picture of the physical environments and the chemical building blocks available to early life is a critical Earth science challenge. Clues to shed light on these mysteries stem largely from investigations of Earth’s ancient rocks and minerals—the only remaining evidence of the time when Earth’s life first emerged.