Chapter 17 The Dynamic Earth

17.1 Structure of the Earth:

•Scientists obtain information about the structure of Earth through __direct__ and ___indirect______observations.

Direct observations include analysing rock directly from Earth’s interior.

-Volcanoes – lava flows-Rock samples

Indirect observations include measuring gravitational force differences around the globe to infer the density of material beneath Earth’s surface.

-Measuring of magnetic fields and gravity

-Observations of how earthquake waves travel through the layers (next unit you will learn more on this!)

Modern Mapping:

-satelliteariel photos-GPS-Infrared and radar images

At one time the continents formed Pangea, A single huge landmass

DO CYU 17.1 p. 496 # 1-11

17.2Evidence of a Dynamic Earth:

Continental Drift Theory: The surface of the Earth moves constantly- First proposed by Wegner based on the following evidence:

-Puzzle fit of continents

-Geological coastline matches

-Fossil matching

-Coal deposit matching

-Equatorial glacial evidence

Unfortunately his theory was not accepted until when HOW the continents moved was better understood!

DO CYU 17.2 p. 500 #1-7

17.3 NewEvidence of a Dynamic Earth:

  1. Mid-Ocean Ridges & Maps

Mid-oceanic ridges are undersea mountain ranges

The discover of mid-ocean ridges where the sea floor was spreading, as well as trenches where continents and oceanic plates met etc. were mapped along with known locations of high volcanic and earthquake history and this showed the boundaries of the “plates” See Fig 1 p. 501

  1. Sea-Floor Spreading

When basalt cools the iron particles in the rock align with the earths magnetic field (like tiny compass needles) and since the magnetic poles reverse over earth history, this has created a pattern

Radioactive dating When they looked at the mid-ocean ridges closer it was discovered that the rock was youngest at the ridges, and oldest at the trenches where the oceanic plates dip under the continental plates

Magnetic Evidence there is also a pattern of magnetic shifts that can be observed moving away from the divergent ocean ridges that show that new plate is forming and moving outward from both sides of this boundary. See Fig 3. P. 503

17.4 Theory of Plate Tectonics:

The theory of plate tectonics states that the lithosphere is divided into 12 large segments and about 20 smaller ones.

The lithosphere is divided into 12 sections called plates plus 20 smaller ones. These tectonic plates “float” on top of the dense fluid like asthenosphere which creates a push-and-pull on these plates due to large slow moving convection current within it, causing many different plate boundary phenomena

, mountaints,

Summary of Plate Movement

Plate Boundary / Description of Movement / Geological Formations / Picture
Convergent
Ocean-Ocean / Subduction zone
Island Arc Volcanoes
Convergent
Ocean-Continent / Subduction zone
Trench
Volcanoe belt
Mountains
Earthquakes
Convergent
Continent-Continent / Mountain Range
Divergent / Oceans = ridges
Continent = Rifts /
Transform / Earhquakes
Faults

Chapter 18 – Plate Tectonics

18.1 Causes and Effects of Plate Movement:Shaping the Earth:

Push: out at divergent boundary where sea floor spreading is occuring

Pull: down at subductions zones

Convection: created when the core heats the liquid like mantle which then cools as it rises … and is density dependant

CYU 18.1 p. 521 #1-10DO Worksheet with new seating partners

18.2: Geological Events:

Volcanoes: - mark cracks in the lithosphere where magma & gas reach the surface

-Found at:

  • Mid-Ocean Ridges
  • Volcanic Belts - Parallel to convergent ocean-continental boundary (on continent)
  • Volcanic Island Arcs – parallel to convergent oceanic-oceanic boundary
  • Hot Spots – above a spot of very hot mantle. Often resulting in Volcanic island chainseg. Hawaii Is.

Earthquakes:- mark locations where transform boundaries form faults

Epicenter – location directly above the focus

Focus – location where the earthquake originated underground

P OR COMPRESSIONAL WAVES – Primary (faster)

Travels in the same direction as the wave

Can travel through solids, liquids and gasses

S OR SHEAR WAVES –Secondary (slower)

Travels perpendicular to the wave direction

Can travel through solids only

***P waves travel faster (about 1.7x) than s waves

What do P-waves and S-Waves provide indirect evidence for?

1Distance to the Epicenter: since the p wave and s wave travel at different speeds, the time interval between when they reach a seismograph can be used to determine the distance from the epicents

2Indirect information about the layers of the earth:tells us the depth,

density and state of the different layers of the earth