Universe, Moon and the Earth

2020-04-28 23:21:11

Universe, Moon and the Earth

Moon and the Universe

Origin of Earth - Theories

Nebular hypothesis : by Immanuel Kant revised by Laplace : planets were formed out of a cloud
Binary theory : by Chamberlain and Moulton : wandering star came near formation of cigar shaped extension separated and condensed to form planets

Modern Theories

Big Bang Theory was first proposed by Georges Lemaitre in 1931.
- All matter in one tiny ball
- exploded 13.7 bil years ago -> first atoms.
- Temp dropped - atomic matter
- universe became transparent.
Hoyles’s concept of steady state : Universe roughly the same at any point in time

Formation of Stars and Planets

Stars are formed by localised clumps in a Nebula
Stages in the development of planets are :
- core of a nebula becomes surrounded by a rotating disc of gas and dust due to gravitational force
- cloud condenses -> round objects planetisimals
- Which come together to form planets
1st 4 planets are Terrestrial and others called Jovian/Gas Giant

Jovian	Terrestrial
Core is denser	Core not dense
Spin more and are flattened at the poles	Spin less hence poles are less flattened
more moons	less
Have mostly H2 and He in atmosphere	Have CO2 and N2

Moon

Dumb bell theory by George Darwin - Earth expelled a piece of its mass
large body collided into Earth and formed the Moon was the Big Splat Theory
Moon Craters created by 2 processes : volcanism and cratering.
- largest - South-Pole Aitkin basin.
lack water, atmosphere and techtonic plates reason for little erosion.

[[kegy202.pdf]] - Origin and Evolution of the Earth NCERT

Evolution of Earth

Formation of lithosphere : heavier materials sank towards the centre, lighter ones came up cooled and formed crust

Atmosphere

Stages in evolution of present atmosphere are :

Initially made of Hydrogen and Helium/primordian atmosphere lost due to solar winds
Hot interior released gases and water vapour called Degassing
Leading to the formation of an early atmosphere containing water vapour, N2, NH3, CO2, CH4, contained little free oxygen.
Life conc in oceans; photosynthesis saturated oceans w/ O2 which then flooded out
Atmosphere is composed of Gases, Water vapour and Dust particles
- Water Vapour
  - in warm tropics account for 4% of air by volume, less than 1 in poles and deserts
  - absorbs part of insolation, prevents E from becoming too hot or cold
- Dust
  - conc in lower layers, air currents can take them higher
  - subtropical and temperate regions have higher conc due to dry winds blowing
  - act as Hygroscopic nuclei

Structure

Troposphere
- Avg height 13km, 8 near poles 18 near equator; temp dec as we go higher
- contains dust, water vapour; all climatic/weather changes takes place here
- Air temp at Tropopause is -80C
Stratosphere
- Extends upto 50km; Contains the Ozone layer
Mesosphere
- Extends upto 80km; Temp dec w/ inc in height reaching 100 C
Ionosphere
- from 80 - 400km; contains charged ions that reflect Radio waves
- Temp inc w/ height

Interior of the Earth

Exogenic : from outside and Endogenic : from inside the Earth shaped the landscape of the Earth.

Sources of Information

Direct Sources of information of the Earth are

Surface rocks
Rocks from Gold mines
From Deep Ocean drilling projects.
Volcanic Eruption

Indirect sources of information about the interior of the Earth are

Depth of the Earth - leads to inc in Temp, Pressure
Meteorites - similar material
Seismic Waves
Gravity - diff gravity at places, most at Poles least over Equator
Magnetic Field - distribution of magnetic material

Earthquakes

point where the energy of a quake is released is called a Focus or a Hypocenter on the surface it is called epicentre.
Hypocenter/ Focus is point of release of Energy
Point on the surface nearest to Focus is Epicentre
All earthquakes take place in Lithosphere
Intensity measured through Mercalli scale(0 -12), Magnitude by Richter. Mercalli takes into account visible damage by the event.
foci in areas of mid oceanic ridge are at shallow depths and in Alpine Himalayan belt are deep seated

1. Body Waves

generated due to release of energy at focus.
move in all direction
further divided into- P and S waves.
Primary Pwaves
- faster and first to arrive at surface
- Move through Solid, Liquid and Gas and are similar to sound waves
- vibrate parallel to direction of the wave -> stretching and squeezing of material
- shadow zone b/w 105deg - 145deg
Secondary S-waves
- through only Solids; more destructive
- last to record on seismograph
- travel perpendicular to waves and cause crest and troughs
- shadow zone lies beyond 105deg

2. Surface Waves

formed when Body waves interact with surface rocks
velocity and direction changes depending on the material density

The Various types of Earthquakes are :

Tectonic Earthquakes
- Volcanic Earthquakes : special class of techtonic earthquakes.
Collapse Earthquakes : intense mining leads to roofs collapsing
Explosion : of chemical or nuclear weapons.
Reservoir Induced

Structure of the Earth

Crust

Oceanic crust (5km) thinner than continental (30km) crust
oceanic crust rock is Basalt
brittle, thicker under Mountains
density from 2.7-3 gm/cm3

Mantle

Extends from Mohos discontinuity to 2900 km has density of 3.4gm/cm3
Upper portion is asthenosphere (astheno=weak) upto 400km contains most of the Magma
Crust and upper mantle is called Lithosphere 100-200km

Core

Extends from 2900km to 6300km
Outer core is Liquid and inner core in solid state
Density varies from 5 - 13 g/cm3
Mostly consists of Nickle and Iron aka Nife layer

Volcanoes

Shield Volcanoes

largest of all eg Hawaiian.
mostly made up of Basalt very fluid.
generally low exlosive until water gents into the vent.

Composite Volcanoes

Eruptions are cooler and more viscous than basalt
Along with lava pyroclastic material and ashes are given out accumulates in the vent openings making the mouth appear as composite volcano.

Caldera

most explosive, often collapse on themselves forming depressions called caldera
magma source is closer and bigger than others

Flood Basalt Provinces

Very fluid lava travels long distances it is also thick more than 50m
Eg the deccan traps.

Mid Ocean ridge volcanoes

stretches more than 70,000km
central portion experiences frequent eruptions

Volcanic Landforms

Depending on the cooling of the lava, igneous rocks are classified as volcanic rocks and plutonic rocks
Rocks that cool in the crustal portion takes different forms called the Intrusive forms
Dome shaped, granite bodies of cooled magma chamber formed in deeper depths of crust and appear on the surface after erosion are called Batholiths
Large dome shaped intrusive bodies connected by pipe like conduits from below, localised sources of lava are called Laccolith. Eg Domal hills of granite rocks in Karnataka.
Horizontal flow of lava forms a saucer shape concave to the sky body Found at base of synclines and top of anticlines are called Lopoliths.
Phacoliths are are conduits that source lapoliths from magma chambers
Thin and Thick horizontal bodies of intrusive igneous rocks are called sheets and sills
When lava solidifies perpendicular to the ground and cools at the same position to develop a wall like structure are called Dykes. Found in Maharashtra they were feeders for the eruptions that formed Deccan traps.

Distribution of Oceans and Continents

Continental Drift

Alfred Wegner in 1912 put forward continental drift theory.
single continental mass Pangea (split into 2 Laurasia and Gondwanaland) and mega ocean called Panthalassa

Evidence in support of continental drift

Jig saw fit of continents
Rocks of same age across oceans suggesting no ocean existed b/w them
Tillite : sedimentary rock formed out of deposit glaciers found in India are also found in all six diff landmasses in the southern hemisphere
Placer deposits of gold in Ghana but source rock is missing
Distribution of Fossil
According to Wegner Polar fleeing force ie rotation of the Earth and Tidal force i.e. attraction of moon and sun were responsible, found to be untrue.

Post Drift Studies

Arthur Holmes put forward the Convectional Current Theory it said radioactive elements cause thermal difference leading to the formation of currents in the mantle.
- Mobile rock beneath plates move in a circular manner, heated material comes up cools and goes back down again. Process repeats endlessly forming a current.
- Radioactive decay and Residual heat are reasons source
Rocks equidistant from the Mid Oceanic Ridge volcanoes had similar properties
[[Oceans and Coastal Landforms]]

Plate Techtonics

Plate tectonics theory was put forward by Mckenzie and Parker in 1967
Tectonic plates are Massive irregularly shaped slab of solid rock composed of continental and oceanic lithosphere.
7 major and other minor plates
What are the types of plate boundaries :
- Divergent Boundaries eg Mid Atlantic Ridge, generates new crust
- Convergent Boundaries : forms the subduction zone where one plate dived into another
- Transform Boundaries : plates slide horizontally past each other, crust neither produced nor destroyed
Indian Plate aka Indo Australian
- Continent convergence along Himalayas forming a subduction zone
- Tethys sea separated Eurasian plate(part of Laurasia) and Indian Plate (part of Gondwana)
- During movt lave outpoured forming the Deccan traps

Diastrophic Plateaus :

Name of Plateaus	Properties
Intermontane Plateaus	highest and largest show variety of topographic features Eg Tibettan Plateau
Mountain Border Plateaus	Piedmont plateau b.w Atalntic coast and Appalachian mountain is an example
Domed Plateaus	Plateau of Ozark in USA is an example
Volcanic Plateaus	---
Erosional	found particularly in semi-arid regions and have cut away portions of high lands

[[kegy203.pdf]] - Interior of the Earth [[kegy215.pdf]] - Life of the Earth