LEO UPSC CLASSES BLOG
02.06.2021 GEOGRAPHY CLASS – 7th class
Topics revision of last class:
Earth’s layers – internal structure of the Earth : Crust, mantle, core
Shadow zones – Types of seismic waves – Types of Earthquakes – Earthquake measurements – Side effects of Earthquakes : Landslide, forest fire, tsunami etc.
Characteristics of Earth Landform :
Surface of earth - ocean 70.8% and land 29.2%.
One third of the earths surface is occupied by Pacific Ocean.
Northern hemisphere (i.e.) the portion to the north of the equator has a majority of landmass.
Southern hemisphere (i.e.) the portion to the south of the equator has a majority of ocean.
The prime meridian is a geographical reference line that passes through the Royal Observatory, Greenwich, in London, England.
Indian Standard Time is calculated on the basis of 82.5 degrees east longitude.
IST is ahead of GMT by 5:30 Hours.
Antipodal arrangements :
Two diametrically opposite points in the surface of the earth due to its spherical shape.
44.6% ocean - ocean
1.4% land- land e.g.:
Iberian Peninsula - New Zealand
Northern China - Patagonian Desert
Validation: by comparing their latitudes and longitudes coordinates
Continental drift theory of Alfred Wegener 1912:
Aim : Climatic variations in the world
Basis:
Carboniferous – Pangea
SIAL floats on SIMA (continent floats on ocean)
Force of Buoyancy - Buoyancy is the force that causes objects to float. It is the force exerted on an object that is partly or wholly immersed in a fluid.
Pole fleeing force – centrifugal force (Radiates outwards) - continents moves towards north or the pole.
Tidal force of sun and moon (East – west movement) E.g., The movement of North America from East to west.
Process:
Mountains are formed when two landmasses collide. For e.g., Atlas, Alps, Himalayas. (Equator ward movement and west ward movement)
The formation of the Rocky in North America and the Yandes in South America is due to the friction of SIAL on SIMA. (N- S running mountains).
Evidences:
Jigsaw fit
Rocks of the same age across oceans
Glacial evidences - tillite
Distribution of fossils
Cynognathus – fossil evidence of the Triassic land reptiles (type of dinosaur)
lystrosaurus
Glossopteris – 300 million years ago a plant species
Mesosaurus
Timeline:
Permian 250 million years ago: Single large landmass was called Pangea and single large water body was called Panthalassa
Triassic 200 million years ago : Landmass divided into two – Laurasia and Gondwana – the waterbody separating the two was called Tethys sea
Jurassic 145 million years
Cretaceous 65 million years ago
Limitations:
Against his aim
Capacity of tidal forces
N-S running mountains SIAL and SIMA friction
Arthur Holmes 1930 magnetic convective force
Convection current – vertical movement of heat transfer – pushing the continents
Harry Hess (deep sea diver) – 1960 sea floor spreading - waxing( forming) of Atlantic and wanning (disappearing) of Pacific Ocean .
Plate tectonics theory Parker and McKenzie 1967:
3 types of plate boundary:
Divergent plate boundary
When two plates move away from each other then that plate boundary is called divergent plate boundary. Where the new crust is generated due to the rising of magma from interior of the earth. The raised crust is called as mid oceanic ridges also known as constructive plate boundary.
Convergent plate boundary
When two plates move towards each other due to density differences. One plate subduct beneath the other plates thus there is a loss of part of earth crust hence this plate boundary also called destructive or consuming plate boundary.
This plate boundary is responsible for origin of trenches, volcanoes, fold mountains.
Higher density plate becomes subduct – oceanic plate density high than continental plate.
Transform plate boundary
When two plates slides past each other then it is called Transform Plate boundary.
E.g., San Andrea’s fault.
Major Tectonic Plates:
Pacific plate
North American plate
South American plate
African plate
Eurasian plate
Indo Austrliaan plate
Antarctica plate
Credits : Leo B Brindha
