The Origin and Evolution of the Earth

Nebular hypothesis

It is by a German philosopher Immanuel Kant.

In 1796 Mathematician Laplace revised it.

The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun. The sun is 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.

The nebular hypothesis is a widely accepted theory that explains the formation and evolution of our solar system. Proposed by Immanuel Kant and further developed by Pierre-Simon Laplace in the 18th century, it suggests that the Sun, planets, and other celestial bodies formed from a rotating cloud of dust and gas, called a solar nebula.

Key points of the nebular hypothesis:

Formation of the Solar System: According to this theory, the solar system began as a massive, rotating cloud of gas and dust called the solar nebula. This nebula began to contract due to gravitational forces.

Formation of the Protostar: As the nebula contracted, it started to spin faster and flatten into a spinning disk. The center became increasingly dense, forming the protostar (which eventually became our Sun), while the surrounding material formed a flattened disk known as the protoplanetary disk.

Planetesimal Formation: Over time, within the protoplanetary disk, smaller particles began to collide and stick together, forming larger objects called planetesimals. These planetesimals further collided and accreted to form protoplanets, which eventually became the planets in our solar system.

Differentiation and Formation of Planets: As these protoplanets continued to grow, they underwent differentiation, with heavier materials sinking toward their cores and lighter materials rising to the surface. This process led to the formation of the distinct layers observed in planets.

Formation of Moons and Other Bodies: Moons and other celestial bodies such as asteroids and comets were formed through similar processes of accretion and gravitational interactions within the protoplanetary disk.

The nebular hypothesis provides a comprehensive explanation for the observed patterns and compositions of the planets, their moons, and other celestial bodies within our solar system. While refinements and details have been added over time, the basic framework of this hypothesis remains a foundational concept in understanding the formation of planetary systems in the universe

Binary theories

When discussing the evolution of Earth, "binary theories" might not be a commonly used term. However, certain theories or concepts related to the Earth's evolution involve binary elements or opposing viewpoints:

1. Catastrophism vs. Uniformitarianism: This can be seen as a binary contrast in early geological theories. Catastrophism, proposed by Georges Cuvier, suggested that Earth's geological features were primarily shaped by sudden, catastrophic events like floods or earthquakes. In contrast, Uniformitarianism, advocated by James Hutton and later refined by Charles Lyell, posited that geological processes observed today (like erosion or sedimentation) have operated consistently over vast periods, gradually shaping the Earth's surface.

2. Punctuated Equilibrium vs. Gradualism: In the realm of biological evolution, the debate between punctuated equilibrium and gradualism represents another binary theory. Punctuated equilibrium, proposed by Stephen Jay Gould and Niles Eldredge, suggests that species often undergo long periods of stability (stasis) interrupted by rapid evolutionary changes (punctuations). Gradualism, on the other hand, suggests a steady, gradual change in species over time, as proposed by Charles Darwin.

3. Plate Tectonics: Continental Drift vs. Fixed Continents: In the past, there was a binary debate between the idea of fixed continents and the theory of continental drift. Alfred Wegener proposed the theory of continental drift, suggesting that continents were once connected as a single landmass (Pangaea) and later drifted apart. This theory eventually led to the development of plate tectonics, which is widely accepted today, describing the movement of Earth's lithospheric plates

Big Bang Theory

The most popular argument regarding the origin of the universe is the Big Bang Theory or Expanding Universe Hypothesis by Edwin Hubble in 1920.

The universe is expanding as time passes, and galaxies move further and further apart.

Stages of the development of the universe.

1. In the beginning universe existed in one place in the form of a tiny ball with an unimaginably small volume, infinite temperature and density.
2. At Big Bang the tiny ball exploded violently. This leads to huge expansion that took place 13.7billion years to the present.
3. Within 300,000 years from the big bang, the temperature dropped to 4,500 kelvin and gave rise to atomic matter.

The expansion of the universe means increasing the space between the galaxies.

The star formation

The initial density differences gave rise to the differences in gravitational forces and it caused the matter to get drawn together. These formed the bases for the development of galaxies.

A galaxy contains a large number of stars.

Galaxies are spread over vast distances that are measured in thousands of light-years.

The diameters of individual galaxies range from 80,000- to 150,000 light-years.

A galaxy starts to form by the accumulation of hydrogen gas in the form of a very large cloud called Nebula.

Eventually, the growing nebula develops localized clumps of gas. These clumps continue to grow even denser gaseous bodies giving rise to the formation of stars.

The formation of stars is believed to have taken place some 5-6 billion years ago.

Light travels at the speed of 300,000 km per second.

The light from the sun reaches earth in 8.311 minutes. The distance between the sun to the earth is 149,598,000 km.

Formation of planets

The stages in the development of Planets

1. The stars are localized lumps of gas within a nebula. The gravitational force within lumps leads to the formation of a core to the gas cloud and a huge rotation disc of gas and dust develops around the gas core.
2. In the next stage the gas cloud starts getting condensed and the matter around the core develops into small rounded objects. These small-rounded objects by the process of cohesion develop into what are called planetesimals. Larger bodies start forming the collision and gravitational attraction causes the material to stick together. Planetesimals are a large number of smaller bodies.
3. In the final stage these large number of small planetesimals accrete to form a fewer large body in the form of planets.

All the planets are formed in the same period about some time about 4.6 billion.

Our solar system

Our solar system consists of the sun [star] and eight planets 63moons, millions of the smaller bodies like asteroids and comets and a huge quantity of dust- grains and gases.

Out of eight planets, Mercury, Venus, Earth and Mars are called the inner planets. These are terrestrial, which means Earth-like as they are made up of rocks and metals and relatively high densities. They lie between the sun and the belt of asteroids.

The other four planets are outer planets made up of Jovian or gas giant planets. Jovian means Jupiter-like.

 These are larger than terrestrial planets and have a thick atmosphere, mostly of helium and hydrogen.

The international astronomical union removed Pluto from the planets list. It is considered a dwarf planet.

Difference between the terrestrial and Jovian

The Moon

The moon is the only natural planet to the Earth.

In 1838, Sir George Darwin suggested that the earth and moon formed a single rotating body [dumb- bell-shaped body], and eventually broke and created a depression occupied by the Pacific Ocean.

A body of the size of one to three times that of Mars collided with the Earth, Sometimes after the Earth was formed.

They blasted a large part of the earth into space.

 Then it continued to orbit of the earth and eventually formed the present moon about 4.44 billion years ago.

Evolution of the Earth

The planet earth initially was a barren, rocky and hot object in a thin atmosphere of hydrogen and helium with a layered structure.

From the outermost end of the atmosphere to the centre of the earth, the material that exists is not uniform.

From the surface to the deeper depths, the earth’s interior has different zones.

The evolution of Earth is an immense and complex narrative encompassing billions of years, characterized by numerous geological, biological, and environmental changes. Here's an overview of key stages in Earth's evolution:

Formation of Earth: Approximately 4.6 billion years ago, the solar system began to form from a cloud of dust and gas. Over time, particles accumulated, leading to the formation of Earth.

Hadean Eon: During the earliest phase, the Hadean Eon, Earth underwent extreme conditions with intense volcanic activity, frequent impacts from asteroids, and a harsh environment inhospitable to life.

Formation of Oceans and Atmosphere: Around 4 billion years ago, as Earth cooled, water vapor condensed to form oceans. The atmosphere gradually developed, rich in volcanic gases but lacking in oxygen.

Archean and Proterozoic Eons: During these eons, life likely emerged. Simple single-celled organisms, such as bacteria and archaea, appeared in the Archean, followed by more complex life forms in the Proterozoic.

Oxygenation and the Great Oxygenation Event: Around 2.4 billion years ago, photosynthetic organisms began releasing oxygen as a byproduct of photosynthesis, leading to the "Great Oxygenation Event," significantly altering Earth's atmosphere.

Phanerozoic Eon: This eon began around 540 million years ago and continues to the present day. It is characterized by the diversification of life forms, including the Cambrian Explosion, when complex multicellular organisms rapidly appeared.

Continental Drift and Plate Tectonics: About 200 million years ago, the supercontinent Pangaea began to break apart, leading to the movement of continents to their present positions. This process continues today through plate tectonics.

Ice Ages and Climate Variations: Earth has experienced various ice ages and periods of significant climate change, including warm periods like the Mesozoic Era (age of dinosaurs) and colder epochs like the Pleistocene, which featured multiple ice ages.

Human Evolution: Over the last several million years, human ancestors evolved and diversified, leading to the emergence of modern humans, Homo sapiens, roughly 300,000 years ago.

Modern Era and Human Impact: The last few thousand years have seen significant human impact on the planet, including agriculture, industrialization, and rapid environmental changes, leading to concerns about climate change, biodiversity loss, and ecological disruptions

Evolution of the Lithosphere

The earth was mostly in a volatile state during its primordial stage.

The Gradual Increase in Density Increases the Inside Temperature, Results Separation of Material Depends on Their Density.

As a result, heavier materials go through the centre of the earth and lighter ones move towards the surfer of the earth.

With time Is Not Falter And Solidified And Condensed With That Smaller One.

This later led to the development of the 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 crust, mantle, outer core and inner core.

From crust to the core, the density of 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.

In the first stage the loss of the 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.

 During the cooling of the earth, gases and water vapour were released from the interior solid earth which started the evolution of the present atmosphere.

The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and 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 gets dissolved in rainwater and the temperature further decreased causing more rains.

The rainwater falling onto the surface got collected in the depressions to give rise to the oceans.

 Origin of life

The last phase in the evolution of the earth relates to the origin and evolution of life.

 The earth or even the atmosphere of the earth was not conducive to the development of life.

The earth has a huge size and changing nature of its interior composition. Due to this, it is not possible to know about the interior of the earth by direct observations.

 The earth’s radius is 6,370 km. Humans can't reach the centre of the earth.

Through mining and drilling operations we have been able to observe the earth’s interior directly for a depth of a few kilometres.

The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.

Sources of Information about the Interior of the Earth

Direct sources

Rocks from the mining areas

Scientists overworld working on different projects to explore the conditions in the crustal portions.

Deep Ocean Drilling Project and Integrated Ocean Drilling Project are two important projects.

The deepest drill at kola, in the Arctic Ocean, has so far reached the depth of 12 km.

Volcanic eruptions

Indirect sources

Analysis of properties of matter indirectly provides information about the interior.

Meteors are not from the interior of the earth but the material and the structure are similar to that of the earth.

Gravitation is greater near the poles and less at the equator.

Gravitational anomaly is the change in gravity value according to the mass of material, giving us information about the distribution of mass materials in the crust of the earth.

Magnetic sources

Seismic waves

Earthquake is shaking the earth.

It is caused due to release of energy, which generates waves to travel in all directions.

The point where energy is released is called the focus or hypocentre of the earthquake.

The point on the surface of the earth is called the epicentre.it is the point directly above the focus.

Earthquake waves

All-natural earthquakes take place in the Lithosphere [the portion of depth up to 200 km from the surface of the earth].

Seismographs are instruments used to record the motion of the ground during an earthquake.

Earthquake waves are basically of two types- body waves and surface waves.

Body wave moves through the interior of the earth, as opposed to surface waves that travel near the earth's surface.

There are two types of body waves-P and S waves.

P- Waves or primary waves move faster and reach the surface. These are similar to sound waves and parallel to the direction of the wave.

P-waves travel through gases, liquid and solid materials.

The body waves interact with the surface rocks and generate a new set of waves called surface waves. These are secondary waves.

S-waves arrive at the surface with some time lag and travel only through solid material.

S- Waves are perpendicular to the wave direction, hence these are more destructive, and they cause the displacement of rocks leading to the collapse of the structures.

The emergence of the shadow zone

The shadow zone is the zone of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves.

 It results from P waves being refracted by the liquid core and S waves being stopped completely by the liquid core.

Types of earthquakes

The most common ones are tectonic earthquakes. These are generated due to the sliding of rocks along a fault plane.

A volcanic earthquake is caused by the movement of magma beneath the surface of the Earth. 

Collapse earthquakes are small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface.

Explosion earthquakes are produced by the detonation of chemicals or nuclear devices.

The earthquake events are scaled according to the Magnitude or intensity of the shock.

The magnitude scale is called the Richter scale and is expressed in absolute numbers 0-10.

The intensity scale is named after Mercalli, an Italian seismologist. It takes into account the visible damage. The range of the intensity scale is from 1-to 12.

The immediate hazardous effects of the earthquake area, Ground shaking, differential ground settlements, land and mudslides, soil liquefaction, ground lurching, avalanches, ground displacement, floods from dam and levee failures, fires, structural collapse, falling objects and tsunami.

The effect of the tsunami would occur only if the epic centre of the tremor is below the oceanic waters and the magnitude is high.

Tsunami waves are generated by tremors and not an earthquake themselves.

The quakes of the high magnitude are rare and tiny types occur every minute.

Structure of the Earth

The Crust

It is the outermost layer of the earth and is made up of heavier rocks.

The thickness of the crust varies under the oceanic is 5 km and continental is around 30 km and mountains as 70 km in Himalaya region.

The Mantle

The mantle is the mostly-solid bulk of Earth's interior. The mantle lies between Earth's dense, super-heated core and its thin outer layer, the crust

The upper portion of the mantle is called the asthenosphere and extends up to 400 km.

The crust and the uppermost part of the mantle are called Lithosphere. its thickness ranges from 10-to 200 km.

The Core

The outer core is liquid state and the inner core is solid state. It is referred to as the nife layer.

The boundary between the mantle and outer core is at the depth of 2900 km.

Centre of the earth is 6,300 km.

The core is made up of heavier metals mostly constituted by nickel and iron.

Volcanoes and Volcanic Landforms

A volcano is defined as an opening in the Earth's crust through which lava, ash, and gases are erupting.

Shield volcanoes

These are the largest volcanoes on the earth, for example, the Hawaiian volcanoes.

Active volcanoes are mostly made up of basalt [a type of lava that is very fluid when it erupts].

Composite volcanoes

These volcano eruptions are cooler and more viscous lavas than basalt.

Caldera

These are the most explosives in the earth's volcanoes.

They tend to collapse on themselves rather than build any tall structure.

The collapsed depressions are called calderas.

Flood basalt provinces

These volcanoes outpour highly fluid lava that spreads long distances.

Some parts of the world are covered by thousands of km of thick basalt lava flows.

The lava thickness is 50-100 meters, and the Deccan traps from India, presently covering the Maharashtra plateau.

Mid–Ocean Range Volcanoes

These volcanoes are occurring in oceanic areas and their ridges more than 70,000 km long that stretch through all the ocean basins.

Volcanic Landforms

Intrusive forms

Volcanic landforms are divided into extrusive and intrusive landforms based on whether magma cools within the crust or above the crust.

Intrusive landforms are formed when magma cools within the crust and the rocks are known as Plutonic rocks or intrusive igneous rocks.

Lacoliths

These are larger dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below and located in the deeper depths.

The Karnataka plateau is spotted with domed hills of granite rocks.

Lalith, phytolith and sills

An igneous intrusion is associated with a structural basin, with contacts that are parallel to the bedding of the enclosing rocks.

A phytolith is a pluton of igneous rock parallel to the bedding plane or foliation of folded country rock. 

The near horizontal bodies of the intrusive igneous rocks are called sill or sheets. The thicker one is called sheets and the thinner one is called sills.

Dykes

When lava makes its way through cracks and the fissures developed in the land and solidifies almost perpendicular to the ground.

It gets cooled in the same position to develop a wall-like structure called dykes.

These are mostly found in intrusive forms in the western Maharashtra area.

These are considered the feeders for the eruptions that led to the development of Deccan traps.