sicenecs

SCIENCE

 

  • Layers of the Earth

3 main layers: crust, mantle, core (lithosphere, convecting mantle, dense metallic core)

5 mechanical layers: lithosphere, asthenosphere, mantle,outer core, inner core

 

CRUST

  • Ocean & land = oceanic & continental crust.

Continental crust= 20-90 km/ 2.7g cm = less dense

  • Made up of more rock types. More pores (spaces)

Oceanic crust= 5-10 km/ 3.9 cm = denser

  • The minerals have higher amounts of iron & magnesium
  • Smaller pores higher density

 

*oxygen is the most common element in the crust. But it's not only oxygen though.

*cold= denser, hot= less dense

*depth is directly proportional

*more compressed higher pressure

MANTLE

  • Solid but capable of flow
  • Thickest layer in earth 70% of Earth’s mass
  • Solid Rock! Not liquid
  • Convection Currents- it is the fluid or magma flow in the mantle. Mostly happens in the middle mantle, rises up when cold then falls back down to heat up.

CORE

Outer Core

  • Molten (liquid) metal
  • Composed of the melted metals are iron and nickel

Inner Core

  • Solid sphere composed mostly of iron
  • Heat in the core is probably generated by the radioactive decay of uranium and other elements
  • It is solid because of the pressure from the outer core, mantle, and crust compressing it tremendously

Lithosphere

  • Consists of the solid upper mantle and crust
  • Broken into plates that move over the atmosphere
  • 12 major plates

Asthenosphere

  • Part of upper mantle (entirely upper mantle rock)
  • Behaves plastically and slowly flows

 

  • Plate Tectonic Theories

 

Continental Drift

  • Alfred Wegener in the early 1900’s proposed the hypothesis that continents were once joined together in a single large land mass he called Pangea (meaning “all land” in Greek.)
  • He proposed that Pangea was split apart and the continents had moved gradually to their present positions - a process that became known as continental drift.
  • He died due to collecting ice samples in Greenland
  • Pangea about 200 million years ago
  • Gondwana- southern potion of pangea
  • Laurasia- northern portion of pangea
  • Panthalassa Ocean- is the name of the ocean surrounding the whole pangea.

Wegener’s Evidence for Continental Drift

  •  Fossils of plants and animals of the same species found on different continents.
  • Rock sequences, same rock sequences have seen similarities in different continents like india and australia
  • Continents fit together like puzzle pieces (example, atlantic coastlines of africa and s. america)
  • His ideas were rejected because there was no mechanism for continents motion that he proposed for this to happen.

 

Seafloor Spreading

  • Harry Hess- made a discovery that would vindicate wegener. He proposed the seafloor spreading theory.
  • Proposed that hot, less dense material below Earth’s crust rises toward the surface at the mid-ocean ridges.
  • Scientists found that the youngest rocks are located at the mid-ocean ridges.
  • New seafloor ganun

Trench- a long, narrow, deep depression in the ocean bed, typically one running parallel to a plate boundary and marking a subduction zone.

RADAR(Radio Detecting & ranging)

SONAR(Sound Navigating & Ranging)- frequently used.

Mid Ocean Ridge- a central valley on an ocean floor at the boundary between two diverging tectonic plates where new crust forms from upwelling magma.

Findings that support Seafloor Spreading Theory:

  1. Rocks are younger at the mid-ocean ridge
  2. Rocks far from the mid-ocean ridge are oler
  3. Sediments are thinner at the ridge
  4. Rocks at the ocean floor are younger than those at the continents.

Mirror Copies- pattern of the seafloor

*the rocks closest to the central ridge are the youngest, the older rocks are found near coastline

 

SCIENCE II

  • Mechanism of Plate Tectonics

Seafloor Spreading provided insight to the mechanism for how the continents moved

  • Magma gets pushed up at the mid ocean ridges and creates new lands while the subduction zones gobble up the land on the other side of the plates.

Convection Current is the driving force of plate tectonics. They provide enough energy to move the plates in the lithosphere.

  • Plate Boundaries & Distribution

World Plates

  • Earth’s crust divided into 12 major plates which move in various directions
  • The plate motion makes them collide, pull apart, and scrape against each other
  • Each type of interactions are the causes of the earth’s “tectonic” features (hills, mountains)
  • Tectonic, refers to the deformation of the crust as a consequence of plate interaction.

 

The moving plates interact with each other along their boundaries, these interactions produce volcanoes and earthquakes; volcanism and earthquakes occur along plate boundaries. (refer to figure 1)

Figure 1, plate boundaries

 

Three Different Plate Boundaries

  1. Divergent Boundaries
  2. Convergent Boundaries
  3. Transform Boundaries

 

• Divergent Boundaries

  • Boundaries where two plates are diverging, moving away from each other
  • As the plates move away, the rocks break and create earthquakes
  • Molten rocks (magma) comes up through the cracked creating volcanoes
  • Sometimes in continental crust, when the land is being pulled apart, it creates a valley, water fills up the cracks and creates linear lakes.
  • Most d.b’s are found in the seafloor

LANDFORMS FROM D.B

  • Volcanoes from continental rifting
  • Linear Lakes
  • Rift Valleys
  • Mid-Ocean Ridges

EXAMPLE OF D.B

  • Iceland’s volcanoes are running through the middle of the country
  • Red Sea rift

 

• Convergent Boundaries

  • Boundaries where two plates are converging, moving towards each other

 

Three Types of Convergent Boundaries

  1. Continent-Continent Collision
  • Forms mountain ranges

e.g  Europeans Alps, Himalayas

2.             Continent-Oceanic Crust Collision

  • Called as subduction, where oceanic lithosphere subducts underneath the continental lithosphere
  • Oceanic lithosphere heats and dehydrates as it subducts
  • The melt forms volcanism, e.g Andes

3.             Ocean-Ocean Plate Collision

  • When two oceanic plates collide, one runs over the other which causes it to sink creating a subduction zone
  • The subducting plate is bent downwards to form a very deep depression called a trench
  • World’s deepest parts of the ocean are found in trenches, e.g Mariana’s Trench (11 km deep

 

• Transform Boundaries

  • Are boundaries between two plates that are sliding horizontally past one another
  • e.g San Andreas Fault Line,

Connection between Earthquakes and Plate Tectonics

  • At boundaries between plates, friction causes them to stick together. The built up energy causes them to break, earthquakes occur

 

Connection between Volcanoes and Plate Tectonics

  • Volcanism is mostly found at plate boundaries/margins
  • E.g Pacific Ring of Fire

 

Volcanoes are formed by:

  • Subduction
  • Rifting
  • Hotspot

 

Hotspot Volcanoes

  • Hot mantle breaching the surface in the middle of a tectonic plate, e.g hawaiian islands

  • The tectonic plate moves over a hotspot forming a chain of volcanoes (refer to figure 4)

  • The volcanoes get younger from one end to another

  • Older and dead volcanoes turn into volcanic islands or sea mounts