Distribution of Oceans and Continents - Chapter 4 Geography NCERT Class 11

Summary

This educational video explores the distribution of oceans and continents, highlighting the theories of continental drift by Alfred Wegener and seafloor spreading by Harry Hess. It explains how Earth's surface, once a single landmass, has dramatically changed due to forces like convection currents and plate tectonics. The video also delves into the evidence supporting these theories, such as matching coastlines and the distribution of fossils, and discusses the movement of the Indian plate, contributing to the formation of the Himalayas.

Takeaways

• 🌍 Earth's surface is 71% ocean and 29% land, earning it the nickname 'Blue Planet'.
• 🌱 The distribution of oceans and continents has changed significantly over time, with continents once forming a single landmass.
• 📜 The theory of continental drift, proposed by Alfred Wegener, suggested that continents were once joined and have since drifted apart.
• 🔍 Evidence for continental drift includes matching coastlines, similar rock ages, and the distribution of fossils and Placer deposits.
• 🌀 The concept of convection currents in the Earth's mantle was proposed by Arthur Holmes, providing a mechanism for continental movement.
• 🌋 The mapping of the ocean floor revealed underwater mountains, trenches, and mid-ocean ridges, adding new dimensions to the study of Earth's structure.
• 🌌 The seafloor spreading theory, proposed by Harry Hess, suggested that new oceanic crust is formed at mid-ocean ridges and pushes older crust aside.
• 🏔 The formation of the Himalayas is a result of the convergent boundary between the Indian and Eurasian plates, where one plate is pushed under another.
• 🔮 The theory of plate tectonics, which unifies the concepts of continental drift and seafloor spreading, explains the movement of Earth's lithosphere.
• 📏 The movement of tectonic plates is measured in millimeters per year, with the forces driving this movement originating from the Earth's mantle.

Q & A

What percentage of Earth's surface is covered by oceans?

71% of Earth's surface is covered by oceans.

Why is Earth sometimes referred to as the 'Blue Planet'?

Earth is referred to as the 'Blue Planet' due to the abundant water on its surface, which covers 71% of the planet.

What was the initial observation that led to the theory of continental drift?

The initial observation was the similarity in coastlines on either side of the Atlantic Ocean, which suggested that they were once joined together.

Who proposed the theory of continental drift?

The theory of continental drift was proposed by a German meteorologist named Alfred Wegener.

What were the two forces suggested by Alfred Wegener as reasons for continental drift?

Alfred Wegener suggested that the forces behind continental drift were 'pole fleeing force' and 'tidal force'.

Why was Wegener's theory of continental drift initially rejected?

Wegener's theory was initially rejected because the forces he proposed were considered inadequate to cause the continents to drift.

What was the major contribution of Arthur Holmes to the understanding of Earth's structure?

Arthur Holmes proposed the concept of convection currents operating in the Earth's mantle, which became a basis for rejecting the continental drift theory.

What is the significance of mid-ocean ridges?

Mid-ocean ridges are long chains of underwater mountains formed due to volcanic eruptions and are significant as they provide evidence for seafloor spreading.

How did the mapping of the ocean floor contribute to the understanding of continental drift?

Mapping of the ocean floor revealed that it has a similar uneven surface to landmasses, with mountain ranges and deep trenches, which provided new evidence against Wegener's theory.

What is the concept of seafloor spreading?

Seafloor spreading is the concept that new oceanic crust is formed at mid-ocean ridges through volcanic activity, and this crust then moves away from the ridges as new material emerges.

What is plate tectonics and how does it relate to the distribution of oceans and continents?

Plate tectonics is the theory that Earth's lithosphere is divided into several plates which move over the mantle. This movement of plates explains the distribution of oceans and continents and the processes of continental drift.

What are the three types of plate boundaries?

The three types of plate boundaries are divergent boundaries, where plates move apart; convergent boundaries, where plates move towards each other; and transform boundaries, where plates slide past each other.

How are the movements of the Indian plate described?

The Indian plate initially broke away from the Australian plate and moved northwards towards the Eurasian plate, leading to the formation of the Himalayas due to convergent movements.

Outlines

00:00

🌏 Overview of Earth's Oceans and Continents

The video begins by highlighting that Earth's surface is 71% ocean and 29% continent, earning it the nickname 'Blue Planet'. It introduces the concept that the current distribution of land and water was not always the case, and that understanding how and why these changes occurred is crucial. The video promises to delve into the theories and evidence gathered by scientists and philosophers to explain Earth's structure, starting with the theory of continental drift.

05:02

🌍 Continental Drift Theory

The script discusses the theory of continental drift, which suggests that continents were once joined and have since drifted apart. It credits Dutch mapmaker Abraham Ortelius for the initial observation and German meteorologist Alfred Wegener for formulating the theory in 1912. Wegener proposed that continents were drifting due to 'pole fleeing force' and 'tidal force', although these reasons were later deemed inadequate, leading to the theory's rejection. The video also mentions a separate video on the evidence supporting continental drift.

10:03

🔍 Post-Drift Studies and Seafloor Mapping

Post-drift studies, following the rejection of Wegener's theory, explored further using ocean floor mapping. This new research revealed that the ocean floor is not flat but has a varied terrain, including mountain ranges and deep trenches. Scientists discovered mid-ocean ridges formed by volcanic eruptions and found that rocks from these ridges were younger than those from continental areas. These findings provided new evidence that contributed to a better understanding of Earth's dynamics.

15:05

🌐 Plate Tectonics and Earth's Movement

The script introduces the concept of plate tectonics, which suggests that the Earth's lithosphere is divided into plates that move. It explains the three types of plate boundaries: divergent, where plates move apart; convergent, where plates move towards each other; and transform, where plates slide past each other. The video also discusses how scientists measure the rate of plate movement and the forces behind it, such as convection currents in the mantle.

20:06

🏔️ Formation of the Himalayas and Indian Plate Movement

This section details the movement of the Indian plate, its separation from the Australian plate, and its convergence with the Eurasian plate, leading to the formation of the Himalayas. It discusses the geological events that occurred as the Indian plate moved, including volcanic eruptions that formed the Deccan Traps. The script also describes the current position of the Indian plate and its interactions with other plates, emphasizing the dynamic nature of Earth's crust.

25:08

📚 Conclusion and Educational Summary

The video concludes by summarizing the three key theories discussed: continental drift, seafloor spreading, and plate tectonics. It emphasizes that plate tectonics is now the widely accepted theory for explaining the distribution of oceans and continents. The script invites viewers to explore more educational content and subscribe for updates, highlighting the importance of understanding Earth's geological processes.

Keywords

💡Continental Drift

Continental drift is a theory proposed by Alfred Wegener that suggests the Earth's continents were once joined together in a single landmass known as Pangaea. This concept is central to the video's theme as it sets the stage for understanding the historical distribution of land and sea. The script mentions how the coastlines of the Atlantic Ocean on both sides show similarities, suggesting they were once a single landmass that later broke apart.

💡Pole Fleeing Force

The Pole Fleeing Force is a term used in the context of Wegener's continental drift theory to describe the force that supposedly caused landmasses to move away from the South Pole. Although later deemed inadequate, it illustrates early attempts to explain continental movement. The video discusses how this force, along with tidal force, was considered insufficient to cause the observed drift.

💡Tidal Force

Tidal Force refers to the gravitational pull exerted by celestial bodies like the Moon and the Sun, which affects the Earth's oceans and tides. In the script, it was initially proposed as a force contributing to continental drift. However, it was later rejected as a primary mover due to its insufficient strength.

💡Convection Current Theory

Convection Current Theory, introduced by Arthur Holmes, suggests that the movement of semi-molten rock in the Earth's mantle generates currents that can move the tectonic plates. This theory is significant to the video's narrative as it provides a more plausible mechanism for continental movement than the forces proposed by Wegener.

💡Mantle

The mantle is the layer of the Earth between the crust and the core, and it plays a crucial role in the video's discussion of plate tectonics. The upper part of the mantle, known as the asthenosphere, is more plastic and subject to convection currents, which are key to understanding how the Earth's surface changes over time.

💡Mid-Oceanic Ridges

Mid-Oceanic Ridges are underwater mountain ranges, often formed by volcanic activity. They are mentioned in the script as areas where new oceanic crust is formed through volcanic eruptions. These ridges are critical to the sea floor spreading theory and serve as evidence for the dynamic nature of the Earth's surface.

💡Sea Floor Spreading

Sea Floor Spreading refers to the process by which new oceanic crust is formed at mid-ocean ridges and pushes older crust away from the ridge. This concept, proposed by Harry Hess, is central to the video's exploration of how the Earth's surface changes and is a key part of the plate tectonics theory.

💡Plate Tectonics

Plate Tectonics is the theory that the Earth's lithosphere is divided into several plates which move over the mantle. This theory, which builds upon the concepts of continental drift and sea floor spreading, is the main focus of the video. It explains the distribution of oceans and continents and the geological activity at their boundaries.

💡Divergent Boundaries

Divergent Boundaries are locations where two tectonic plates move apart from each other, often resulting in the formation of new crust, as seen at mid-ocean ridges. The video uses the example of the Mid-Atlantic Ridge to illustrate how this process contributes to the distribution of land and sea.

💡Convergent Boundaries

Convergent Boundaries occur when two tectonic plates move towards each other, resulting in one plate being forced under the other in a process known as subduction. This can lead to the formation of mountain ranges, such as the Himalayas, which the video discusses as a result of the Indian plate's collision with the Eurasian plate.

💡Transform Boundaries

Transform Boundaries are where two plates slide past each other horizontally. These boundaries can cause earthquakes but do not create or destroy crust. The video mentions these as part of the broader plate tectonics theory, highlighting the different ways plates can interact.

Highlights

Continents cover 29% of Earth's surface, while oceans cover 71%, earning Earth the nickname 'Blue Planet'.

The distribution of oceans and continents has changed significantly over time.

Continental drift theory suggests that continents were once joined and have since drifted apart.

Alfred Wegener proposed the continental drift theory in 1912, suggesting continents are moving.

Pole fleeing force and tidal force were Wegener's initial reasons for continental drift, but were later deemed inadequate.

Post-drift studies introduced new evidence from ocean floor mapping, challenging earlier theories.

Convection current theory, proposed by Arthur Holmes in 1930, suggests mantle convection as a driving force for continental movement.

Ocean floor mapping revealed underwater mountain ranges, deep trenches, and other geological features.

Mid-ocean ridges are formed by volcanic eruptions and are the longest mountain chains on Earth.

Rock samples from mid-ocean ridges are younger than those from continental areas, indicating recent volcanic activity.

Ocean floor is divided into continental margins, abyssal plains, and mid-ocean ridges based on depth and relief.

The distribution of earthquakes and volcanoes correlates with plate movements and is evident in the ocean floor.

Sea floor spreading is a key concept that explains how new oceanic crust is formed and how it affects continental drift.

Plate tectonics theory, introduced in 1967, suggests that the Earth's lithosphere is divided into plates that move.

There are seven major and several minor plates that make up the Earth's lithosphere.

Plate movements are categorized into three types: divergent, convergent, and transform boundaries.

The movement of plates is driven by convection currents in the Earth's mantle.

The Indian plate's movement and its impact on the formation of the Himalayas is a significant example of plate tectonics in action.

The chapter concludes with a discussion on the three major theories that explain the distribution of oceans and continents.

Transcripts

in this video we're going to read about

the distribution of oceans and

continents today continents cover 29% of

the total surface of the Earth and the

rest that is 71% is covered by ocean

bodies that is the reason planet Earth

is also called as Blue Planet due to the

Abundant water on its surface when you

look at the world map the distribution

of ocean bodies and land mass how they

are today it was not like this earlier

it was something like this so in this

chapter we will understand how why and

what made them change so much that it

changed from the picture on your left to

the picture on your right we will also

learn how scientists came to know about

this because scientists and philosophers

are the ones who formed theories and

collected evidence regarding the

structure of the earth therefore it gets

very fascinating to know about their way

and methods of coming to a conclusion

which everyone of us today are reading

about let's begin with the first topic

continental drift Contin Al drift is a

theory based on the fact that if you

look at the coastline of both side of

Atlantic Ocean which is these two places

basically you will see some similarity

it looks as if they were together as one

land mass once upon a time and then it

broke apart and because of this

observation scientists believed that the

two American continents then Europe and

Africa they were once joined together

initially there was this Dutch map maker

Abraham atius who came up with this

observation about the three continent

being together but in 1912 it was a

German meteorologist by the name of

Alfred Wagner who gave a comprehensive

argument in the form of continental

drift theory because he thought that the

continents are drifting away from each

other I've made a separate video on this

topic the theory of continental drift

and the evidence in support of this

Theory you can find both the videos Link

in the description please have a look at

it so far we have studied about what is

the continental drift theory and what

are the evidences in support of the

continental drift theory now we are

going to read about the forces behind

continental drift theory Alfred Wagner

the person who suggested the theory of

continental drift he suggested that

there were two reasons behind it first

one is pole fleeing force and the second

one is tidal Force let me tell you in

quick what these two forces are by the

name pole fleeing Force we can think of

something that is fleeing away or

running away from the pole in this case

we are talking about the land mass that

is fleeing away from the South Pole

because in initially it was considered

that Pang was originated near South Pole

and the Earth's centrifugal forces

caused Pang to break apart and the

resultant continents to drift towards

Equator the second force that was

suggested by Vaga was the tidal force it

is due to the attraction of the Moon and

the Sun that develops tide in Oceanic

water so WEA believ that it is due to

these two forces that worked for

millions of years led to Breaking of

continents now there is a Twist in this

Theory most Scholars considered these

forces to be totally inadequate meaning

they did not find enough strength in

these two reasons that was suggested by

wager which ultimately led to the

rejection of his theory so please

remember it is due to the invalid

reasons presented by vager led to the

rejection of his theory on Continental

Drift and those invalid reasons were

pole fleeing forces and tidal Force now

we are going to read about post drift

studies meaning after the rejection of

vean continental drift theory there were

some more research and studies done so

that it would be better to know that

what if there are some unknown Avenues

which were left unexplored now the

problem with vag's theory on Continental

Drift was the evidence which were

completely focused towards landmass in

fact they were collected from landmasses

so if you remember from the video

evidence in support of continental drift

theory Again the video link is in the

description we spoke about distribution

of fossils of Flor and FAA or deposits

like Delite so all these evidences were

focused towards landmar now Alfred

Wagner proposed his theory on

continental drift in 1915 that was the

time of World War I a number of

discoveries during the post-war period

added new information to geological

literature particularly The information

collected from Ocean flow mapping

provided New Dimensions for the study of

distribution of oceans and

continents now let's read about what are

those new information that came out the

first one is convectional current theory

now what is the meaning of the word

convectional convection is the circular

motion that happens when warmer air or

liquid which has faster moving molecules

making it less dense Rises while the

cooler air or liquid drops down so how

does rainfall occur when warm air that

goes up it holds a lot of liquid

basically the moisture part and when it

condenses the warmer air is cooled the

mo moisture inside it it breaks into

liquid molecules and it falls down as

rain now in the similar sense there's

this person called Arthur Holmes in 1930

he said that there is a possibility of

convection current operating in the

mantle portion now if you remember

anything from the video different layers

of the earth there I have discussed that

the Earth is divided into these layers

right crust mantle and core and

especially mantle is divided into two

parts the upper mantle and lower mantle

and the upper mantle is also called as

asthenosphere which means weaker layer

so Arthur Holmes is basically saying

that there is a convection current which

is operating in this part of the earth

which is the upper mantle because here

all the rock is in molten State and

there is this motion going on wherein

the wherein the molten rock is moving in

a circular path and that is what makes

this layer very weak so Arthur Holmes

says that there exists a system of such

currents in the entire mantle potion so

this was a very major contribution to

our understanding of how the earth works

and this also became the basis on which

the Contemporary scientists discarded

the continental drift theory so I hope

you understood the convectional current

theory now we're going to read about

mapping of the ocean floor by the very

name you can understand that it speaks

about mapping or exploring the ocean bed

so while mapping the scientists found

that ocean floor is not just a vast

plane but it is full of relief meaning

it has similar uneven surface like we

have on landmar there are mountain

ranges as well as deep trenches and then

deep valleys in the ocean bed so

trenches are deep cavity or crack in the

ocean bed they usually occur when two

continental plates move apart there's

another thing called the mid Oceanic

ridges ridges are long mountain ranges

now imagine how there could be a long

mountain range inside the ocean and the

reason behind that is due to volcanic

eruptions so always remember right under

the crust we have the mantle mantle is

again of two types that is upper and

lower mantle but this mantle consists of

molten rocks that keeps circulating that

is why the mantle is not a stable layer

of the Earth so whenever there is a

volcanic eruption the magma comes out of

the oceanic crust it then becomes

solidified Rock after cooling this

solidified rock is also known as oceanic

crust and this oceanic crust after

repetition forms Oceanic rich rich

bridge is an uplifted land mass that

looks like a mountain range so what the

scientists did was they took samples of

rock particles from this Ridge area as

well as from the Continental area they

just wanted to experiment and see

whether which one of them is younger in

terms of age and it turned out that the

sample of rocks that were collected from

The Ridge area is younger and that has

to be obviously younger because the

volcanic eruption is happening every now

and then so newer molten rocks are

forming layers of oceanic crust and this

was an interesting finding which made

the post- drift studies more real and

valid now we're going to read about

ocean flow configuration here the entire

ocean flow has been divided into three

segments and it has been done purely

based on the depth as well as relief

meaning based on the looks let's read

about each segment of the ocean floor

the first one is Continental margin by

The Heading you can again figure out

that it's talking about area between the

shore that is Continental Shore and deep

sea bessin

if you are on a beach as you go further

towards the sea you'll notice the land

form shows depression as a result the

water level increases like this there

will be a point where the water gets

really deep and from above it looks deep

blue that is the deep sea bessin so this

area is called the Continental margin

and this consists of continental shelf

continental slope which is the land

depression then continental rise and

deep Oceanic trenches again trenches

mean deep cavity which occur when two

continental plates move apart the second

one is Abyssal Plaines so Abyssal means

very very deep we are talking about deep

plains that lie between Continental

margin and mid Oceanic ridges so I have

explained you what is Continental margin

and what is mid Oceanic ridges so the

area in between is called the abysal

plane there's something special about

this place all these sediments that is

the mud or Rock particles it gets

deposited here so if you see there is

land depression as we move away from the

continent towards deep sea due to this

natural depression all the mud particles

or sediments it moves downwards it moves

towards the abysal plane and the third

component of ocean floor is mid Oceanic

ridges I've explained what they are they

are long chain of mountain system within

the ocean it is also the longest

mountain chain on Earth but it is inside

the ocean water and these rich occur due

to intense vol iic activity when the

magma comes out of the mantle it breaks

the oceanic crust so that the molten

rocks can come out and after cooling it

forms layers of crust this is how there

is an upliftment that makes it a rich

now we are going to read about the

distribution of earthquakes and

volcanoes for this we are going to refer

to this figure the big black dots

represent hot spots which basically

means that here the magma comes out of

the mantle that's why they are referred

to as Hotpot spots many such hotpots are

located in ocean floor and there are few

on Continental mass as well the next you

see the tiny black dots these are places

where you will find a volcano many of

them are located on Continental mass and

a few in ocean

floor then we have these tiny gray dots

forming a long line sort of a thing

these are regions of shallow earthquake

and they are found on Ocean bed they are

also known as mid Oceanic ridges and

I've explained what mid Oceanic rides

are they occur due to movement of

continental plates and if you see

earthquakes are Tremors originating from

plate

movements at last we have the gray

shaded regions they are deep earthquake

zone again they are part of mid Oceanic

ridges but these are deeper ones and a

very active earthquake zone so if you

look at the grish area near Indian

Himalayan region this region is very

unstable because the Indian and uian

plates are constantly converging and

creating tension so this this was the

entire distribution of earthquakes and

volcanoes that we saw with the help of a

figure now we go on to the topic concept

of seaf flow spreading now this is where

things get really interesting so you

remember Alfred Wagner's continental

drift theory in case you haven't seen

the video I recommend you do so the

video link is in the description or you

can also click on the info card on top

vag's Theory focused more on the

Continental evidence like the fossils of

animals found in various Continental

landmasters then how the South American

east East Coast kind of looked like a

missing puzzle when joined with the

African West Coast so things like that

were Alfred Wan's arguments now what

happens is the post- drift studies gave

some valid arguments and information

against Wagner's continental drift

theory especially mapping of the ocean

floor and testing of oceanic rocks were

very crucial steps that were taken by

the scientists they revealed some real

facts that gave the post- drift study

good amount of weight when compared to

Wagner's continental drift theory I know

things are getting a little confused

using so what I'm going to do is create

a nice differentiation between both the

theories side by side so that it makes

clear sense as to what is what and it

will also serve as a quick revision so

on your left hand side is the

continental drift theory given by Alfred

Vagner and on your right hand side is

the post- drift studies which were done

by various scientists just to prove the

point that there are reasons much more

Beyond What wagonner

suggests the continental drift theory

talks about the matching of continents

Wagner said if you look at South America

and Africa they look like a jigsaw

puzzle fit when brought closer which is

true that once upon a time both land

masses were together but the reason

behind that is much more deeper than

just merely looking at the world map and

saying they were ones together the

second point in continental drift theory

talks about the fact that rocks from

different continents were of the same

age and this point made Vaga believe

that the land masses were once together

and they slowly drifted away again the

reason behind the drifting is much

deeper than just looking at rocks and

saying they all are same the third point

in continental drift theory talks about

tillite formation the Gana land consists

of six land masses they are India Africa

Madagascar Australia Antarctica and

folkland Islands under the base of these

six land masses teite sediments were

found so that made Vaga think that okay

these six land masses were once together

and now they are aart so this is a

pretty good observation however the

reason is much bigger and in depth

rather than observing Delights

the fourth point in continental drift

theory talks about Placer deposits they

are deposits of Rich minerals like gold

diamonds Etc so if you look at the coast

of Ghana and then coast of Brazil you'll

see that these Placer deposits looks

like Wayne that were once joined

together this point again made vagona

believe that Africa and South America

was once a single landmar and the last

point in continental drift theory talks

about distribution of fossils when

identical species of plants and animals

were found on landmasses it made Vaga

strongly believe that once upon a time

there was only a single landmass and

with time it started splitting into

different continents so these were the

evidences of Alfred wager that made him

come up with the continental drift

theory now coming to the right hand side

that is the post drift studies after the

World War II many discoveries were made

which added new information scientists

started arguing the fact that Alfred

Vagner only looked at evidences that

were collected from the Continental

areas which is true if you look at the

left hand side all these evidences were

taken by simply looking at the land

masses so in the post- drift studies the

scientists felt hey why don't we do some

comprehensive study by mapping the ocean

floor and that led to the convectional

current theory where Arthur Holmes said

it is because of the magma present in

the mantle which is causing the ocean

flow to expand since the oceanic crust

is thinner than the continental crust

therefore it is easy for the magma to

come out from the ocean bed and that's

why the mid Oceanic ridges give a solid

proof about this Theory and the second

point in post- drift theory is the

mapping of ocean floor when the ocean

floor was being mapped scientists saw

that ocean bed is not a flat piece of

land it has similar terrain uneven

surface just like we have on land this

was an astonishing finding and then they

also went on to find mid Oceanic ridges

on the ocean bed which are these long

range of mountains that were formed due

to the rocks that came out of the mantle

in the form of magma and when scientists

took samples of rock from the mid

Oceanic ridges as well as from the

Continental side they found that the

rocks from the mid Oceanic Ridge were

comparatively younger in age hence they

concluded as we move away from the mid

Oceanic ridges the age of the Rocks

increases so this was the post- drift

studies which totally focused on the

concept of sea flow spreading that is

the ocean flow gets pushed to the

opposite side due to volcanic eruption

at the crest and making the sea flow

spread and it was presented by Harry hes

in

1961 whereas the continental drift

theory by Alfred Wagner focused on the

argument that all the continents were

once upon a time a single Continental

Mass named pangi and then the single

Continental Mass began to split into

smaller ones and that's how the world

looks today so if you see two totally

different theories proposed by two

different people hold on we are not done

yet now we have a third concept which

brings us to the topic plate

tectonics now this is the third concept

that tries to answer the questions

related to distribution of oceans and

continents if you see this entire

chapter so far has been trying to answer

the questions related to distribution of

ocean and continents I mean that's what

the title says and we have so far seen

two theories the concept of PL tectonics

was presented by mezi Parker and Morgan

three people in 1967 just after 6 years

of hess's SE floor spreading Theory so

what the plate tectonic Concepts say is

the lithosphere which is also the

combination of crust and upper manle it

is in the form of irregular slab of

solid rock so think of the lithosphere

as a large plate and now when a plate

breaks this is exactly what it looks

like when we say irregular slab of solid

rock this is what the plate tectonics

concept is

suggesting so we know that lithosphere

consists of crust and upper mantle and

the crust is both continent Al as well

as Oceanic in nature the oceanic crust

is thinner than Continental but in

general it is one complete crust hence

the lithosphere covers both ocean as

well as Land And now when we think of a

plate we can easily relate that a plate

consists of land as well as ocean

doesn't matter which of the two occupy a

larger portion of the plate now let's

look at the world map according to this

New Concept which is plate tectonics our

entire Earth surface is divided into

seven major and some minor plates and

the these major plates are the first one

is Antarctica and the surrounding

oceanic plate and the second one is

North American with Western Atlantic

flow separated from South American Plate

along the Caribbean islands plate the

third one is South American with Western

Atlantic floor spread it from the North

American Plate along the Caribbean

islands plate and the fourth one is

Pacific Plate and the fifth one is India

Australia New Zealand plate and the

sixth one is Africa with the Eastern

Atlantic floor plate

and the seventh one is uraia and the

adjacent oceanic plate now let's look at

some minor plates the first one is Cocos

plate which is between Central America

and Pacific Plate then we have nasca

plate that is between South America and

Pacific Plate and then we have Arabian

plate mostly the Saudi Arabian Landmark

then we have Philippine plate between

Asiatic and Pacific Plate and then we

have Caroline plate between the

Philippine and Indian plate north of new

guinia and the last one is Fuji plate

that is northeast of Australia now the

reason this plate tectonic theory is so

interesting is because it makes a very

important argument that continents do

not move in fact continents are part of

these plates and it is the plates that

has been moving throughout the history

of Earth and it will continue to do so

in the future as well I hope you're

getting what I'm trying to say so if you

remember Alfred wner said that initially

everything was one single land mass

named as Pang but it according to new

discoveries it is now believed that Pang

existed due to the convergent mechanism

of plates on which continents reside

convergent means coming closer now we're

going to read about three types of plate

boundaries the first one is divergent

boundaries the meaning of the word

Divergent is pulling away so plates that

moves apart from each other is due to

Divergent mechanism and it creates a

fault or depression which is known as

divergent boundaries places where plates

move away is also known as spreading SES

one such example is the Mid-Atlantic

Rich here the American Plate is

separated from Eurasian and African

plates the second one is convergent

boundaries now convergent is opposite of

Divergent meaning coming closer so what

happens when two plates come towards

each other one plate Dives under another

and it is usually the smaller plate that

converges under the bigger plate leaving

that land area a little uplifted so this

mechanism happens between an oceanic and

Continental plate then between two

oceanic plates and then finally between

two continental plates the third one is

transform boundaries in this mechanism

what happens is the motion of the plate

is horizontal or in other words here the

two plates slide past one another I mean

the best way to imagine is look at this

picture and see how the plates are

moving past one another now that we have

read about different plate movements

it's time to understand what is the rate

at which these plates move I don't know

whether you have seen this program that

used to come on Discovery called strip

the city in that they discussed in one

of the episodes how geologists find the

rate at which the plates are moving it

is very fascinating to see what they do

is they Place sensors all over the

regions to record movs of a plate they

use an instrument called creep meter it

monitors the slow surface displacement

of an active geologic fault in the earth

its objective is to record the tension

that's building up in the Falls they put

two rods attached with steel wire so

when the Surface starts moving it puts

the wire and the geologist measure that

expanding Gap it's usually measured in

millim and roughly a fault moves around

5 to 10 mm a year I recommend you watch

that video in your free time it's really

fascinating we now come to another

important topic what is it that is

making these plates move I mean what is

that Force so when we see Earth we see

this round solid body floating in space

right but I want you to know this solid

body is not

motionless if you have seen my video on

different layers of Earth in that I have

explained the mantle consists of molten

rock and how this magma moves in a

circular manner making the upper mantle

a weak layer and from this weak layer

often heated material Rises to the

surface spreads and then sinks back

again this cycle keeps repeating over

and over to generate what scientists

call a convection cell or convective

flow again you can go back and look at

the convectional current theory that we

discussed under post drift studies so to

answer the question what is the force

that is moving the these plates the

answer is it is the soft mantle and the

circular flow of heated material inside

the earth which is the driving force

behind the plate movement coming to the

last topic of this chapter movement of

the Indian plate okay let me just

quickly wrap up this topic in the most

shortest and simplest form look at this

picture it's the movement of Indian

plate so initially India was part of

this huge Australian plate it was like

India was a large island situated of the

Australian coast and this Australian

plate was part of the Gana land we are

talking about 200 million years ago then

India broke from the Australian plate

and started moving upwards towards the

euroian plate about 40 to 50 million

years ago Himalayas started forming and

it is due to convergent mechanism we

have read about this when two plates

come closer a rapid uplift of land

surface takes place that's how Himalaya

came up before all of this in between

India and Eurasian plate there was the

tetis Sea and the Tibetan block while

moving up upfor roughly around 60

million years ago the Indian plate faced

some events like outpouring of lava and

that's how the decken Trap were formed

and you'll find all ignas rock there so

ignas rock is formed from solidified

lava that's how we are sure of the

volcanic eruption that happened on the

Indian subcontinent the Indian plate

includes Peninsula India and the

Australian Continental portions and then

if you see the Indian plate the

northeastern side it extends through

Rakin yomo mountains of Myanmar towards

the island Ark along the Java trench so

if you see the northeastern side is

going inside of the uran plate a little

bit and on the western side we have the

Arabian plate which extends up to the

Red Sea and then if you go to the

southern part the Antarctica plate so

you can see the oceanic Ridge which is a

divergent boundary it is connected to

the Indian plate so it's kind of a nice

mapping system when you look at these

plates how they are well connected with

each other so anyways that was all about

the movement of the Indian plate so

basically in this chapter we discussed

about three important theories that

shape the reason behind the distribution

of oceans and continents they are

continental drift theory by Alfred wner

then concept of seaf flow spreading

which is referred to as post- drift

theory proposed by Harry hes and then

finally the concept of play tectonics

presented by McKenzie Parker and Morgan

which is now well accepted Theory when

it comes to the reason behind the

distribution of oceans and continents

with this we have come to an end of this

chapter question answer can be found on

the website link is there in the

description thanks for watching and I'll

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