Evidence of Plate Tectonics

1. Evidence of Plate Tectonics • How old is the Earth? • 4.6 Billion Years Old • Has the Earth always looked like it does today? • No, Earth’s past is full of cosmic collisions, Mtn building, and erosion.

2. Early thoughts of Earth’s Past • In the 1700’s, James Hutton (Scottish Chemist) became known as the “Father of Geology.” • He was the first to question how rocks and mountains formed. • What kind of processes would cause their formation and what would cause them to disappear?

3. His questions led to a new concept. • Uniformitarianism – or the concept of Uniformity – is a notion that the same processes that formed Earth in the past are taking place today. • That is to say, the key to understanding the past is understanding the present

4. Geologists – study Earth processes that form minerals and rocks. Geologists examine earthquakes, volcanoes, and tectonic forces. Geologists are also interested in weathering and erosion processes that break-down rock. One unknown fact about Geologists is their fascination with Earth’s past. How did the earth form? This Concept led to the creation of a new Science – Geology!

5. Origin of our Solar System. • 5 Billion years ago a star was born. • This star formed in a stellar nebulae (a collection of gases and star making dust). • This star (our Sun) formed due to a super nova exploding and sending waves of energy through the nebulae.

6. The Nebulae Rotates! • The energy from the super nova caused the nebulae to rotate and pull debris to the center due to the strong gravitational force. • The center heated up and nuclear fusion formed our sun.

7. Planet Formation • With the formation of the Sun, came the force of gravity. • Debris began colliding and clumping together forming our planets. • The denser material, formed the terrestrial planets (Mercury, Venus, Earth, & Mars) closer to the sun – followed by the Gas planets.

8. Cosmic Collisions and Formations! • The gravity from the sun caused the planets to revolve (orbit) around the sun. Earth was the 3rd planet to form. This occurred approximately 4.6 billion years ago.

9. Earth: Dead or Alive • Is Earth dead or alive? • How does one tell if it is alive? • What evidence supports that earth is an active planet?

10. Early Theories of an Active Planet • 1915-1929 – Alfred Wegener argued his theory of “Continental Drift” – which proposed that all continents were joined 255 million years ago forming Pangaea. • What were the 3 main pieces of evidence supporting his theory?

11. Supporting Evidence • 1.) Puzzle-fit of the continents • 2.) Rock Clues – he found the same rock type, formation(s), & rock age in the Appalachian Mtns & in Greenland. • 3.) Fossil Evidence -Mesosaurus – fresh-water reptile found in Africa and South America.

13. Seafloor Spreading • Until the mid – 1900’s, many scientists thought the ocean floor was flat, unchanging, and much older than the continental crust. • The ocean was a great mystery.

14. Seafloor Spreading • Advances in technology allowed scientists to explore new horizons. • Magnetometer – detected changes in the magnetic fields. • “SONAR” – echo-sounding device – used sound waves to map the ocean floor.

15. Seafloor Spreading With SONAR, scientist found the ocean wasn’t all flat but a vast system of underwater mountain chains called ocean ridges appeared. • Along with those ridges, appeared trenches and plains. • The oceanic crust was dynamic and changing just like the continental crust. • The difference was, the oceanic crust was much younger than the continental crust.

16. Seafloor Spreading

17. Seafloor Spreading • Early 1960’s, Harry Hess suggested the Theory of Seafloor Spreading. • Using the available technology, Hess proposed that new oceanic crust was formed at mid-ocean ridges and destroyed at deep-sea trenches.

18. Oceans Explored • While serving in the Navy, Harry Hess became interested in Ocean Geology. • What were the 2 pieces of evidence supporting his theory?

19. Evidence for Seafloor Spreading • Supporting Evidence: • Age of Oceanic Rock – Hess found that the oceanic rocks (180 million yrs) were much younger than continental rocks (4 billion yrs). The youngest were near mid-ocean ridges and as one moved away from the mid-ocean ridge – the age of the rock got older.

20. Evidence for Seafloor Spreading • Magnetic patterns on the seafloor are symmetric in relation to ocean ridges, indicating that ocean crust on either side of the ridge is moving away from the ridge at the same rate.

21. Evidence of Plate Tectonics The theories of Continental Drift and Seafloor Spreading tried to explain what Earth experienced in its past. In the 1960’s, these theories were combined forming the “Theory of Plate Tectonics.” Scientists begin looking for present evidence supporting plate movement.

22. Theory of Plate Tectonics • Scientists combined the theories of Continental Drift and Seafloor Spreading into one theory: Theory of Plate Tectonics – states that Earth’s crust and upper mantle are broken into plates (sections), which are huge rock slabs that move in different directions and at different rates over Earth’s surface.

23. There are 2 types of tectonic plates: Continental Plate Oceanic Plate Continental Plate – is older, thick, and less dense than the oceanic plate. Oceanic Plate – is younger, thin, and very dense. When an oceanic collides with a continental plate – subduction occurs causing the denser oceanic to sink and under cut the lesser dense continental plate. Types of Tectonic Plates

24. Subduction Illustrated

25. Earth’s Interior

26. What Causes Plate Movement? • Convection currents in Earth’s mantle cause tectonic plates to move. • Convection currents occur when a liquid or air heats up and rises due to its lower density. • The liquid rises, expands, cools, and sinks due to its higher density causing a current to occur.

27. Earth’s Interior

28. Evidence of Plate Movement! • Earthquakes – are “vibrations” caused by tectonic forces moving plates. • Both continental and oceanic plates move in relation to each other creating plate boundaries.

29. Plate Boundaries • Plate Boundaries are where most earthquakes and volcanoes occur. • 3 types of Plate Boundaries are: • Divergent –the separation of 2 Plates. • Convergent – the collision of 2 plates. • Transform – the sliding of 2 plates past each other.

30. The 3 Types of Boundaries

31. Plate Movement Explained

33. OH, NO! EARTH SHAKE! • When earthquakes occur as a result of plate movement, seismic waves are produced. • 3 types of seismic waves are: • Primary – P-wave • Secondary – S-wave • Surface – L-wave

34. Seismic Waves • All seismic waves are generated when the rock breaks and move away from the focus. • Each travel at different speeds. • P-wave is the fastest and will go through everything. • S-wave – will not go through the liquid outer core. • L-wave – is the slowest and moves along the surface.

35. Locating the Epicenter: Where the 3 Intersect.

36. Earthquake Magnitude • Richter Scale measures the