Oceanic vs. Continental Crust

• The key differences between oceanic and continental crusts are their composition, density, thickness, age, formation process, tectonic behavior, seismic activity, recycling, topography, heat flow, volcanic activity, and major examples
• Oceanic crust is composed of basalt and gabbro (mafic rocks) and is referred to as SIMA
• Continental crust is composed of granite, feldspar, and andesite (felsic rocks) and is referred to as SIAL
• Oceanic crust is rich in Magnesium and Iron
• Continental crust is rich in Silicon and Oxygen
• Oceanic crust consists of the crust and rigid upper mantle
• Oceanic crust has a lower silica content (45-52%) compared to continental crust
• Continental crust has a higher silica content (60-70%)
• Oceanic crust has a density of ~3.0 g/cm³
• Continental crust has a lower density of ~2.7 g/cm³
• Oceanic crust is thin (5-10 km)
• Continental crust is thick (30-70 km)
• Oceanic crust is younger (0-200 million years)
• Continental crust is older (up to 4 billion years)
• Oceanic crust forms at mid-ocean ridges through seafloor spreading
• Continental crust forms through complex processes over billions of years
• Oceanic crust is frequently subducted at convergent boundaries
• Continental crust resists subduction and leads to mountain formation
• Oceanic crust experiences frequent earthquakes near mid-ocean ridges and subduction zones
• Continental crust experiences earthquakes along fault lines, especially at convergent boundaries
• Oceanic crust is recycled back into the mantle through subduction
• Continental crust is rarely subducted and persists over geological timescales
• Oceanic crust forms ocean basins, mid-ocean ridges, abyssal plains, and trenches
• Continental crust forms mountains, plains, valleys, and plateaus
• Oceanic crust shows higher heat flow at mid-ocean ridges (younger, warmer crust)
• Continental crust exhibits lower overall heat flow (older, more stable crust)
• Volcanic activity is frequent along mid-ocean ridges in oceanic crust
• Continental crust has less frequent volcanic activity, mostly at continental margins and hotspots
• Oceanic crust is found beneath oceans
• Continental crust is found on land
• Seawater has a high sodium chloride content of 77.7%
• River water has a high calcium sulphate content of 60% and low sodium chloride content of 2%

Ocean Deposits

• Zooplankton are crustaceans like krill, jellyfish, radiolarians, and meroplankton, which come in different colors and are mostly translucent
• Phytoplankton include diatoms, cyanobacteria, green algae, and dinoflagellates, which are brown and found in the upper euphotic layer, releasing oxygen
• According to John Murray, ocean deposits are terrigenous and pelagic
• Terrigenous deposits originate from the continents and are brought by rivers and rainwash with half a kg of sediment added for every cubic meter of water
• Terrigenous deposits include gravel, sand, silt, clay, and mud
• Blue mud comes from rocks rich in iron sulphide and organic material, found at the depth of the continental shelf, is blue-black in color, and contains 35% calcium carbonate
• Red deposits are rich in iron oxides and contain 32% calcium carbonate
• Green deposits are the result of chemical weathering, where blue mud changes to green mud due to reaction with seawater, containing green silicate of potassium and gluconite, and 0-56% calcium carbonate
• Volcanic deposits can be from land or the ocean itself and look like blue mud, grey-bluish, or black
• Organic deposits are of oceanic origin
• Neretic deposits are found in shallow water and consist of skeleton and plant remains on the continental shelf, covered by terrigenous deposits; they include shells of mollusks, skeletons of radiolarians, and sponge spicules
• Pelagic deposits are found in deep water and consist of remains of algae, with liquid mud known as ooze
• Calcareous ooze has abundant lime content, high solubility, and is seldom found at greater depths
• Pteropod ooze contains 80% calcium carbonate and pteropod mollusks
• Globigerina ooze is tropical and temperate
• Siliceous ooze is silica-abundant and contains benthic animals
• Radiolarian ooze is dirty grey and contains 5-20% calcium carbonate
• Diatom ooze contains 3-30% calcium carbonate and its color varies by location
• Inorganic deposits precipitate from above and include red clay, containing radioactive substances

Oceanic Zones and Sunlight

• The ocean water column is divided into five zones based on the amount of sunlight they receive
• Epipelagic Zone: It is the sunlight zone with photosynthetic organisms like phytoplankton and temperatures from 34°C to -2°C
• Mesopelagic Zone: Also known as the twilight zone and has sunlight that can't reach to the bottom
• Bathypelagic Zone: Also known as the midnight zone with sharks, squid, and octopuses present
• Byssopelagic Zone: Also known as the abyssal zone, constantly near freezing and has only a few creatures
• Hadalpelagic Zone: Known as the ultra-abyssal zone, is the deepest, mainly in trenches and has a high degree of endemism

Ocean Tides

• Tidal range is the difference between high tide (HT) and low tide (LT)
• Tidal patterns exhibit a delay
• Ebb currents occur approximately every 6 hours and 13 minutes

Spring and Neap Tides

• Spring Tides: Occur when the sun, moon, and earth are aligned (syzygy), resulting in higher-than-average high tides and lower-than-average low tides
• Neap Tides: Occur when the sun, earth, and moon form a right angle (quadrature), leading to lower high tides and higher low tides
• Tropical/Equatorial Tides: Tidal patterns along the Tropic of Cancer, Capricorn, or the equator
• Apogee/Perigee: Tide strength varies with the moon's position; stronger at perigee (closest approach) and weaker at apogee (farthest distance)
• Diurnal Tides: Dominate in high-latitude or enclosed seas, featuring one high and one low tide per lunar day
• Deciding Factors For Tides: Geography, latitude, resonance in ocean basins, and the Coriolis effect

The Lunar Tidal Bulge

• The gravitational force of the moon causes a lunar tidal bulge
• Centrifugal effect leads to a nadir lunar bulge on the opposite side of Earth
• The time it takes for the lunar nodes to complete their cycle of regression takes 18.6 years

Tidal types of cycles

• "Diurnal" Tidal Cycle: A daily tidal cycle exhibiting one high and one low tide
• "Semidiurnal" Tidal Cycle: A cycle with two high and two low tides of approximately equal size each day

Tidal Theories

• Equilibrium Theory (Sir Isaac Newton, 1687): Assumes Earth is covered in water and discusses ideal tides
• Dynamic Theory (Laplace, 1775):Considers that only ¾ of the earth is water
• Progressive Wave Theory (William Whewell, 1883; GB Airy, 1942): Tidal waves are created by the moon's tide-producing force
• Stationary Wave Theory (RA Harris): Waves originate independently in each ocean

Tidal Bores

• Tidal Bore: A wall of water that occurs when a tidal wave enters a low-lying river
• Requires a large tidal range and a bay with a narrow opening
• Examples included Chientang River (China), Petitcodiac River (Canada), and Seine River (France)

Tidal Currents

• Tidal Currents: The upward and downward movement of seawater generated by tides
• Flood Currents: are coastward movements of tides
• Ebb Currents: are returning tides
• Open Ocean Tides are rotary current
• In the open ocean, currents move at 1 km/hr, alternating direction in different hemispheres
• In shallow water, they can reach 44 km/hr, changing directions continuously and are called alternating/reversing currents

Reefs

• Coral reefs are referred to as rainforests of the oceans
• Ahermatypic Corals: Solitary corals without colonies, adaptable to all oceanic conditions
• Hermatypic Corals: Limited to the photic zone of tropical oceans with salinity between 27-30 ppt
• Conditions for Coral Growth: High mean annual temperature (20-21°C), shallow water (60-70 m), clean sediment-free water, and currents/waves (for food)
• Types of Coral Reefs: Fringing, barrier, and atoll
• Fringing Reef: Attached to coastal land along continental margins and a boat channel is formed due to a lagoon
• Barrier Reef: Parallel to coastal platform at a distance
• Atoll: Ring of corals of horseshoe shape with palm trees and a lagoon

Other Reef Related Items

• Faros: Chains of small atolls with lagoons
• Coral Banks: Isolated shapeless reefs
• Coral Pinnacle: Ridges within a lagoon
• Patch Reefs: Mounds above lagoons
• Algae Ridge: Frontal raised part of coral reefs, made of algae, that faces pounding sea waves
• Corallites: Exterior skeletons of corals
• Reef Face: Greater depth and no corals
• Reef Flat: Facing lagoon
• Reef Front: Upper sea-ward portion
• Reef Terrace: Landward side

Theories on Reef Development

• Charles Darwin (1837-42) Subsidence theory: Reefs go through stages of development, they can only grow in shallow oceanic water
• Murray (1880) Stand Still Theory: Coral polyps started growing upwards along the coast at 180 feet
• Daly (1915) Glacial Control Theory: Sea level fell due to glaciations and existing corals died, later new coral polyps began to grow
• WM Davis (1914-18) Subsidence Theory: Grow along subsiding land and is flat due to deposition of marine sediments

Origin of Earth

• Number of Satellites for Mercury and Venus: Zero
• Number of Satellites for Mars: Two
• Number of Satellites for Jupiter: 95
• Saturn has 145 satellites
• Neptune longest year is 164.8 Earth Years
• Venus longest day is 243 days

Theories for Origin of Earth

• Gaseous Hypothesis (Immanuel Kant, 1755): Cold nebula of gas and matter collided, forming rings
• Nebular Hypothesis (Laplace, 1796): Hot nebula cooled, reducing size and increasing speed with outer ring separated
• Planetesmial Hypothesis (Chamberlin, 1905): Revival of Collision Hypothesis with dualistic proto-sun and intruding star.
• Tidal Hypothesis (James Jeans, 1919): Massive star caused tides on the Sun, pulling material that formed planets
• Binary Star (HN Russel, 1937): Stars including the sun and debris started rotating around sun
• Supernova Hypothesis (F Hoyle, 1946): Companion turned into a supernova, leaving dust and energy to form planets
• Interstellar Dust Hypothesis (Otto Schmidt, 1943): Sun passed through a dense interstellar cloud and formed planets
• Cepheid Hypothesis (AC Banerjee): Pulsation of stars, that keeps expanding and contracting

Big Bang Theory

• Big Bang Theory: Postulated in the 1950s and 60s, validated in 1972, it states the universe began as a singularity, followed by rapid expansion
• Cosmic Microwave Background (CMB): Radiation from the Big Bang that can be detected from all directions in space

Isostacy

• Isostacy: Describes the Earth's crust and how it stays balanced by floating on the mantle
• Sir George Airy: Earth's crust has a uniform density, but its thickness varies.
• John Henry Pratt: Earth's crust is of uniform thickness, but the density varies.
• Hayford and Bowie: Height of mountain and oceanic crust varies, but they are balanced out by their densities
• Joly: level of compensation is not linear and 100km is too low
• Heiskenen: Earth's lithosphere bends or flexes under loads like mountain ranges or glaciers.
• Holmes: higher column has lighter material below them of greater depth and smaller column have lighter material below of lesser depth.

Geological Periods

• Hadean Eon: 4 billion years ago
• Archaen Eon: 2.5 billion years ago
• Proterozoic Eon: 2.5 billion to 500 million years ago
• Pre-Cambrian Epoch: 700 million years ago, gas changed to liquid, soft invertebrate animals existed
• Phanerozoic Eon: 500 million years ago to present
• Cambrian Epoch: Ended 500 million years ago, developing vertebrates
• Ordovician Epoch: 440 million years ago, mountain building and vulcanity beginning
• Silurian Epoch: 400 million years ago, leafless plant on land
• Devonian Epoch: 350 million years ago, fish and trees with leaves evolved
• Carboniferous Epoch: 270 million years ago, tallest epoch of palaeozoic with tall green swamps and ferns
• Permian Epoch: 225 million years ago, inland lakes formed with insects
• Mesozoic Era: Ends with Permian Triassic extinction
• Triassic: 180 million years ago, carnivore developed
• Jurassic: 135 million years ago, swamps and flowers evolved
• Creataceous: 70 million years ago, Rockies and Himalayas was initiated
• Cenozoic Era
• Eocene: 40 million years ago, sea floor spreading and modern mammals evolved
• Oligocene: 25 million years ago, mammals such as cats and dogs evolved
• Miocene: 11 million years ago, second upheaval of Himalayas
• Pliocene: 1 million years ago, continents and oceans took the current spot
• Neozoic Era
• Pleistocene: 10,000 years ago and the ice age evolved

Age of tools

• Stone Age: Paleolithic, Mesolithic, Neolithic, Chalcolithic evolved
• Bronze Age wheeled and developed irrigation
• Iron Age – Ended around 500-800 AD

Interior of Earth

• The high density of the core is due to heavy materials
• Fluid or molten outer core is responsible for the Earth's magnetic field
• Magnetic protects against solar wind, atmosphere erosion, and provide the basis for compass navigation
• Tectonically active areas have almost double hotter temperatures at a depth of 40 km than stable areas
• Radioactive materials and heavier elements rose to form the crust

Evidence From Vulcanicity

• Eruption of lava from volcanoes suggests there is a liquid earth layer

Evidence From Seismology

• Primary waves (P waves) and longitudinal and can pass through all states of matter, fastest in solid, and slow at liquids
• Secondary Waves (S waves) and transverse

Discoveries From Richard Oldhum

• S waves disappear at an angular distance of 120° from the epicenter, indicating to S waves being absent from the core in the result of it being liquid
• P and S waves have different velocities and concluded that there are 3 distinct zones of different density

Chemical Composition models

• SIAl is granite and SIMA is basalt
• Suess: crust of sedimentary rocks and low density
• Daly: 3 layers with varied materials
• Jeffery: 4 layers with varied materials
• Holmes: crust and sub-stratum
• Lithosphere consists of the crust and upper solid mantle
• Asthenosphere: upper mantle layer
• Mesophere: lower mantle
• Outer Core: 2900 to 5150 km
• Inner Core: 5150 km to 6371 km deep
• A Mohorovicic discovered discontinuity in velocity and seismic waves
• Thickness of the mantle has less than half of the radius of Earth

Continental and Ocean related items

• Tetrahedral Hypothesis (Lowthian Green): Sphere turns into the tetrahedron and cools with uniform pressure
• Continental Drift Theory (Frank Bursley Taylor): the origin of the Atlantic Ocean, had mountain ranges, collision of drifting continents and had forces driving the movement
• Alfred Wegner: had pieces of geological evidence such as that the continent edges matched nicely like a jig saw, mountain systems, fossils and glaciations