Distribution of Oceans and Continents

Continental Drift

Observe the Atlantic ocean’s coastline, you’ll find the symmetry on either side of the coastline.

It was Abraham Ortelius, a Dutch map maker  who proposed this possibility as early as 1596, Antonio pellegrini who drew map which has continents together.

Alfred Wegener, a german scientist who proposed continental drift theory in 1912  which was on distribution of Continents and oceans

According to Wegener

• All the continents formed on a single Continental mass surrounded by single Mega Ocean
• The super continent named PANGEA which is earth and mega ocean is named PANTHASALA which means all water
• Wegener states around 200 million years ago Pangea was started to split, pangea broke into two large masses i.e

    1.Laurasia

    2.Gondwana

These two formed as North and south components of Continental mass. Laurasia and Gondwana continued to break into smaller continents

Evidences supporting Continental drift theory

Matching of Continents (Jig- saw-Fit)

The shorelines of Africa and South America facing each other have remarkable unmistakable match.

A map produced by computer using a computer programme to find the best fit of the Atlantic ocean margin was presented by Bullard in 1964

Rock of same age across the Oceans

The belt of ancient rocks of 2,000 million years from Brazil matches with those from West Africa.

The earliest marine deposits along the coastline of south America and Africa are from Jurassic Age

Tillite

It is the sedimentary rock formed out of deposits of glaciers

The Gondwana system of sediments from india is known to have its counterparts in six different landmasses of the Southern Hemisphere

At the base system has little indicating extensive and prolonged glaciation. Counterparts of this succession are found in Africa, Falkland island, Madagascar, Antarctica and Australia

The overall resemblance of Gondwana sediments show remarkable similar histories.

The glacial tillite provides unambiguous evidence of Palaeclimates and also drifting continents

Placer deposits

The occurance of rich glacier deposits of gold in the Ghana coast and absolute absence of source rock in the region is an amazing fact

The gold bearing veins are in brazil and it is obvious that the gold deposits of the Ghana are derived from the Brazil Plateau when the two continents lay side by side

Distribution of fossils

When identical species of plants and animals adapted to living on land or in fresh water are found on either side of the marine barriers, a problem arises regarding accounting for such distribution. The observation that Lemurs occur in India, Madagascar and Africa led some contiguous landmass ‘Lemuria’ linking these three landmasses

Mesosaurus is a small reptile adapted to shallow brackish water, the skeletons of these only found in two localities:

i-Southern cape of South Africa

ii-Iraver formations of Brazil

These localties are of 4,800km apart from each other and ocean is between them

Force for Drifting

Wegener suggested that the movement of continents is because of pole fleeting force and tidal force

1. Pole fleeting force-it relates to the rotation of earth, earth has bulge at the equator , this is because of the rotation of earth
2. Tidal force- it is due to the attraction of the moon and sun that develops tides in the ocean

Wegener believed that these forces were much intense since it was million years ago

Post drift theories

A number of discoveries during the World War-II period added new information to geological literature

Conventional current theory

The conventional current theory describes the flow of electric charge within a circuit. It was established before the discovery of the electron and is based on the assumption that current flows from the positive terminal of a voltage source to the negative terminal.

Key points about conventional current theory include:

1. Direction of Current: In this theory, the direction of electric current is considered to be from the positive terminal of a battery or power source, through the circuit, and back to the negative terminal. This direction was assumed before the discovery of the electron.

2. Benjamin Franklin's Model: Benjamin Franklin proposed the idea of positive and negative charges, and initially, scientists believed that positive charges moved within a conductor, creating electric current.

3. Later Discoveries: The discovery of electrons and their negative charge, as well as the understanding of their movement within conductors, led to the realization that the actual flow of negatively charged particles (electrons) constitutes electric current.

4. Conventions in Circuit Diagrams: Despite the actual flow of electrons being from negative to positive terminals (opposite to the conventional current theory), circuit diagrams and electrical engineering practices still use the convention of current flow from positive to negative, which is known as the conventional current flow.

5. Usefulness: While it might seem counterintuitive based on our current understanding of electron flow, the conventional current theory remains relevant in understanding circuit diagrams, analyzing electrical systems, and engineering practices.

The conventional current theory represents an early understanding of electricity that predates the discovery of the true nature of electron flow. Despite its historical origins, it remains an important part of electrical theory and practice

Mapping of the ocean floor

Ocean configuration revealed that the ocean floor is not just a vast plain but it is full of relief

Expeditions to map the oceanic floor in the post-World War II period provided a detailed picture of the ocean relief and indicated the existence of submerged mountains as well as trenches in the ocean, they are closely located to the Continental borders

• The mid-oceanic ridge is found to be the most active volcano in terms of volcano eruptions
• Dating of the rocks from the oceanic crust are found to be much younger from the continental crust
• Rocks on the either side of the ridges and having equi-distant from the crest are found to be remarkably of similar in terms of age and constituents

Ocean floor Configuration

Ocean floor can be segmented into three major divisions based on the depth of as well as the forms of relief

Continental Margins

These form the transition between Continental shores and deep sea basins. these include continental shelf, continental slope, continental rise and deep oceanic trenches

Of these, deep oceanic trenches are the areas which are of considerable interest in so far as the distribution of oceans and continents is concerned

Abyssal plains

These are extensive plains that lie between the continental margins and mid oceanic ridges

Abyssal plains are the areas where the continental sediments that move beyond the margins get deposited

Mid-oceanic ridges

This forms an interconnected chain of mountain system within the ocean

It is the longest chain of mountains on earth that are submerged under the ocean

It is characterized by a central rift system at the crest, a fractionated plateau and flank zone all along its length. Rift system at the center is the zone of volcanoes as mid oceanic volcanoes

Concept of Seafloor spreading

Seafloor spreading is a fundamental geological process that occurs at mid-ocean ridges where new oceanic crust is formed through volcanic activity. This process plays a crucial role in plate tectonics and the movement of Earth's lithospheric plates.

Key points about seafloor spreading include:

1. Mid-Ocean Ridges: These are underwater mountain ranges found in all major oceans. They are characterized by volcanic activity, where magma from the mantle rises up and solidifies, creating new oceanic crust.

2. Plate Tectonics: Seafloor spreading is intimately connected with the theory of plate tectonics. Earth's lithosphere is divided into several tectonic plates that move atop the semi-fluid asthenosphere below. As new crust forms at mid-ocean ridges, it pushes the existing crust away from the ridge in a conveyor belt-like fashion.

3. Oceanic Crust Formation: Magma rises from the mantle through fissures in the mid-ocean ridges, cools upon contact with seawater, and solidifies to form new oceanic crust. This process constantly adds new material to the ocean floor.

4. Ages of Oceanic Crust: By studying the magnetic properties of oceanic crust, scientists discovered alternating patterns of magnetic polarity (stripes of normal and reversed magnetism) on either side of mid-ocean ridges. This led to the confirmation of seafloor spreading and the understanding that new crust forms at these ridges, gradually moving away as new material is added.

5. Divergent Boundaries: Mid-ocean ridges are examples of divergent boundaries, where tectonic plates move away from each other. As new crust forms, it pushes older crust away, leading to the widening of the ocean basin.

6. Subduction Zones: Seafloor spreading is balanced by subduction at convergent boundaries, where older and denser oceanic crust sinks back into the mantle beneath another tectonic plate.

Seafloor spreading provides a mechanism for the movement of Earth's lithospheric plates and the renewal of oceanic crust. This process contributes to the dynamic nature of the Earth's surface and helps scientists understand the history and evolution of our planet's geology

Plate Tectonics

A tectonic plate is a massive, irregularly shaped slab solid rock generally composed of both continental and oceanic lithosphere

The plates move horizontally over the asthenosphere as rigid ones. the lithosphere includes crust and top mantle with its thickness varying from 5km and 100km  in oceanic parts and about 200km in the Continental areas.

A plate is called Oceanic plate or continental plate depending on which of the two occupy a larger portion of the Plate

Pacific plate is an oceanic plate whereas Eurasian plate is largely Continental plate

The theory of plate tectonics proposes that the earth lithosphere is divided into seven major and minor plates

The major plates as follows

1. Antarctica and the surrounding oceanic plates
2. North American Plate- with West Atlantic floor separated from South American plate along the Caribbean islands
3. South American Plate-with western Atlantic floor separated from North American plate along Caribbean islands
4. Pacific Plate
5. India-Australia-New Zealand Plate
6. Africa with eastern Atlantic floor plate
7. Eurasia and Adjacent oceanic plate

Important Minor plates

There are three types of boundaries:

Divergent boundaries:

When new crest is generated as the plate pull away from each other. The site where plates move away from each other is called spreading site

Example: Mid oceanic ridge

 Convergent Boundaries

Where one crust is destroyed and one dive under another, the site where it happens is called Subduction zone

There are three ways in which convergence can happen

1. Oceanic plate and Continental plate
2. Oceanic and Oceanic plate
3. Continental and continental plate

Transform boundaries

Where the crust is neither produced nor destroyed, two plates move horizontally with each other. Transform faults are the planes of separation generally perpendicular to the oceanic ridges

Rates of Plate Movement

The strips of normal and reverse magnetic field that parallel the mid oceanic. The strips of normal reverse magnetic field  that parallel the mid-oceanic ridges help scientists determine the rates of plate movement. These rates vary considerably. The arctic ridge has the slowest rate –less than 2.5cm/year and east pacific rise near eastern island, in the south pacific about 3,400km of west chilie has the fastest rate

Force for the Plate Movement

The mobile rock beneath the rigid plates is believed to be moving in a circular manner. Heated material rises to the surface and spreads and begins to cool an sink back into deeper depths

This cycle is repeated over and over to generate what scientists call Convection cell or Convective flow

Heat within earth comes from two main sources: 1. Radioactive decay 2.Residual heat

The slow movement of hot, softened mantle that lies below the rigid plates is the driving force behind the plate movement

Movement of the Indian Plate

The Indian Plate is a major tectonic plate in the Earth's crust and plays a significant role in the movement and shaping of the Earth's surface. Its movement is associated with various geological processes, including collisions, subduction, and the formation of the Himalayas.

Key points about the movement of the Indian Plate include:

1. Direction of Movement: The Indian Plate is moving in a generally northeast direction at an average rate of about 5-6 centimeters per year. This movement is relatively fast in geological terms.

2. Collision with the Eurasian Plate: One of the most significant aspects of the Indian Plate's movement is its collision with the Eurasian Plate. This collision began around 50 million years ago and continues today.

3. Formation of the Himalayas: The collision between the Indian Plate and the Eurasian Plate led to the uplift of the Earth's crust, resulting in the formation of the Himalayan mountain range. This ongoing collision is responsible for the continuing growth and geological activity in the Himalayas.

4. Tectonic Activity: The collision between these plates has not ceased and continues to cause seismic activity, including earthquakes and the deformation of the Earth's crust in the region.

5. Subduction and Crustal Processes: Along the boundary where the Indian Plate meets the Eurasian Plate, the Indian Plate is primarily experiencing compression and crumpling. Some parts of the Indian Plate might be subducting beneath the Eurasian Plate, contributing to seismic activity.

6. Impact on Regional Geology: The movement of the Indian Plate has had a profound impact on the geological landscape of the Indian subcontinent, leading to the creation of mountain ranges, alteration of river courses, and the formation of numerous geological features.

Understanding the movement of the Indian Plate is essential in comprehending the geological processes shaping the Indian subcontinent and neighboring regions. The ongoing collision with the Eurasian Plate continues to influence seismic activity and geological changes in the area