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evidences_plate.ppt

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1. In 1912, Alfred Wegener proposed the continental drift theory which hypothesized that around 200 million years ago, all the continents were joined together in a supercontinent called Pangaea which later broke apart. 2. Evidence from fossils of the same plants and animals found across continents now separated by oceans, matching rock formations, and coal deposits provided support for continental drift. 3. In the 1960s, the theory of seafloor spreading was developed which helped explain continental drift as new ocean crust is formed at mid-ocean ridges and pushed continents apart.

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evidences_plate.ppt
1.The Continental Drift Theory 2. The Continental Jigsaw Puzzle 3. Evidence From Fossils 4. Evidence From Rocks 5. Coal Deposits 6. The Seafloor Spreading 7. Magnetic Reversal
THE CONTINENTAL DRIFT THEORY In 1912, Alfred Wegener (pronounced as vey-guh-nuhr), a German meteorologist, proposed a theory that about 200 million years ago, the continents were once one large landmass. He called this landmass Pangaea, a Greek word which means “All Earth.”
This Pangaea started to break into two smaller supercontinent called Laurasia and Gondwanaland during the Jurassic Period. These smaller supercontinents broke into the continents and these continents separated and drifted apart since then. Wegener searched for evidences to support his claim. He noticed the fit of the edges of the continents on the opposite sides of the South Atlantic.
 The most visible and fascinating evidence that these continents were once one is their shapes.  The edge of one continent surprisingly matches the edge of another: South America and Africa fit together; India, Antarctica, and Australia match one another; Eurasia and North America complete the whole continental puzzle in the north. THE CONTINENTAL JIGSAW PUZZLE
3. Evidence from Fossils  Fossils are preserved remains or traces of organisms (plants and animals) from the remote past. Fossilized leaves of an extinct plant Glossopteris were found in 250 million years old rocks. These fossils were located in the continents of Southern Africa, Australia, India, and Antarctica, which are now separated from each other by wide oceans. The large seeds of this plant could not possibly travel a long journey by the wind or survive a rough ride through ocean waves. OTHER LINES OF EVIDENCE OF PLATE MOVEMENTS
Distribution of Fossils across Different Continents
Mesosaurus (shown in the next slide) and Lystosaurus are freshwater reptiles. Fossils of these animals were discovered in different continents, such as in South America and Africa. It is impossible for these reptiles to swim over the vast oceans and move from one continent to another. Fossils were also found in Antarctica.
Image of Mesosaurus Fossil
4.Evidence from Rocks  The rocks themselves also provide evidence that continents drifted apart from each other.  Rock formations in Africa line up with that in South America as if it was a long mountain range.  The folded cape mountains of South America and Africa line up perfectly as if they were once a long mountain range.
5.Coal Deposits Coal beds were formed from the compaction and decomposition of swamp plants that lived million years ago. These were discovered in South America, Africa, Indian subcontinent, Southeast Asia, and even in Antarctica.
 The current location of Antarctica could not sustain substantial amount of life. If there is a substantial quantity of coal in it, thus, it only means that Antarctica must have been positioned in a part of the Earth where it once supported large quantities of life.  This leads to the idea that Antarctica once experienced a tropical climate, thus, it might have been closer before to the equator.
6. The Seafloor Spreading  During the 1950s and 1960s, new techniques and modern gadgets enabled scientists to make better observations and gather new information about the ocean floor. With the use of sonars and submersibles, scientists had a clearer view of the ocean floors.  They have discovered underwater features deep within the ocean. Scientists found a system of ridges or mountains in the seafloor similar to those found in the continents. These are called mid-ocean
One of these is the famous Mid- Atlantic Ridge (figure in the next slide), an undersea mountain chain in the Atlantic Ocean. It has a gigantic cleft about 32-48 km long and 1.6 km deep. The ridge is offset by fracture zones or rift valleys.
The Mid – Atlantic Ridge
In the early 1960’s, scientist Harry Hess, together with Robert Dietz, suggested an explanation to the continental drift. This is the Seafloor Spreading Theory.
According to this theory, hot, less dense material from below the earth’s crust rises towards the surface at the mid-ocean ridge. This material flows sideways carrying the seafloor away from the ridge, and creates a crack in the crust. The magma flows out of the crack, cools down and becomes the new seafloor. Overtime, the new oceanic crust pushed the old oceanic crust far from the ridge. The process of seafloor spreading allowed the creation of new bodies of water.
Diagram of Seafloor Spreading
In the place where two oceanic plates collide or where an oceanic plate and a continental plate collide, a subduction zone occurs. As the new seafloor is formed at the mid-ocean ridge, the old seafloor farthest from the ridge is destroyed at the subduction zone. The rate of formation of a new seafloor is not always as fast as the destruction of the old seafloor at the subduction zone.
This explains why the Pacific Ocean is getting smaller and why the Atlantic Ocean is getting wider. If subduction is faster than seafloor spreading, the ocean shrinks. When the seafloor spreading is greater than the subduction, then the ocean gets wider.
Findings that support Seafloor Spreading Theory: 1.Rocks are younger at the mid-ocean ridge. 2.Rocks far from the mid-ocean ridge are older. 3.Sediments are thinner at the ridge. 4.Rocks at the ocean floor are younger than those at the continents.
7. Magnetic Reversal The Earth’s magnetic field is generated in the very hot molten outer core and has already existed since the birth of our planet. The Earth’s magnetic field is a dipole, one that has a North Pole and a South Pole.
evidences_plate.ppt
Magnetic reversal is also called magnetic ‘flip’ of the Earth. It happens when the North Pole is transformed into a South Pole and the South Pole becomes the North Pole. This is due to the change in the direction of flow in the outer core.
 Magnetic reversals happened many times in the past. The occurrence of magnetic reversals can be explained through the magnetic patterns in magnetic rocks, especially those found in the ocean floor. When lava solidifies, iron bearing minerals crystallize. As these crystallize, the minerals behave like tiny compasses and align with the Earth’s magnetic field. So when magnetic reversal occurs, there is also a change in the polarity of the rocks. This allowed scientists to visualize the magnetic stripes in the ocean floor.

More Related Content

evidences_plate.ppt

  • 3. 1.The Continental Drift Theory 2. The Continental Jigsaw Puzzle 3. Evidence From Fossils 4. Evidence From Rocks 5. Coal Deposits 6. The Seafloor Spreading 7. Magnetic Reversal
  • 4. THE CONTINENTAL DRIFT THEORY In 1912, Alfred Wegener (pronounced as vey-guh-nuhr), a German meteorologist, proposed a theory that about 200 million years ago, the continents were once one large landmass. He called this landmass Pangaea, a Greek word which means “All Earth.”
  • 5. This Pangaea started to break into two smaller supercontinent called Laurasia and Gondwanaland during the Jurassic Period. These smaller supercontinents broke into the continents and these continents separated and drifted apart since then. Wegener searched for evidences to support his claim. He noticed the fit of the edges of the continents on the opposite sides of the South Atlantic.
  • 6.  The most visible and fascinating evidence that these continents were once one is their shapes.  The edge of one continent surprisingly matches the edge of another: South America and Africa fit together; India, Antarctica, and Australia match one another; Eurasia and North America complete the whole continental puzzle in the north. THE CONTINENTAL JIGSAW PUZZLE
  • 7. 3. Evidence from Fossils  Fossils are preserved remains or traces of organisms (plants and animals) from the remote past. Fossilized leaves of an extinct plant Glossopteris were found in 250 million years old rocks. These fossils were located in the continents of Southern Africa, Australia, India, and Antarctica, which are now separated from each other by wide oceans. The large seeds of this plant could not possibly travel a long journey by the wind or survive a rough ride through ocean waves. OTHER LINES OF EVIDENCE OF PLATE MOVEMENTS
  • 8. Distribution of Fossils across Different Continents
  • 9. Mesosaurus (shown in the next slide) and Lystosaurus are freshwater reptiles. Fossils of these animals were discovered in different continents, such as in South America and Africa. It is impossible for these reptiles to swim over the vast oceans and move from one continent to another. Fossils were also found in Antarctica.
  • 11. 4.Evidence from Rocks  The rocks themselves also provide evidence that continents drifted apart from each other.  Rock formations in Africa line up with that in South America as if it was a long mountain range.  The folded cape mountains of South America and Africa line up perfectly as if they were once a long mountain range.
  • 12. 5.Coal Deposits Coal beds were formed from the compaction and decomposition of swamp plants that lived million years ago. These were discovered in South America, Africa, Indian subcontinent, Southeast Asia, and even in Antarctica.
  • 13.  The current location of Antarctica could not sustain substantial amount of life. If there is a substantial quantity of coal in it, thus, it only means that Antarctica must have been positioned in a part of the Earth where it once supported large quantities of life.  This leads to the idea that Antarctica once experienced a tropical climate, thus, it might have been closer before to the equator.
  • 14. 6. The Seafloor Spreading  During the 1950s and 1960s, new techniques and modern gadgets enabled scientists to make better observations and gather new information about the ocean floor. With the use of sonars and submersibles, scientists had a clearer view of the ocean floors.  They have discovered underwater features deep within the ocean. Scientists found a system of ridges or mountains in the seafloor similar to those found in the continents. These are called mid-ocean
  • 15. One of these is the famous Mid- Atlantic Ridge (figure in the next slide), an undersea mountain chain in the Atlantic Ocean. It has a gigantic cleft about 32-48 km long and 1.6 km deep. The ridge is offset by fracture zones or rift valleys.
  • 16. The Mid – Atlantic Ridge
  • 17. In the early 1960’s, scientist Harry Hess, together with Robert Dietz, suggested an explanation to the continental drift. This is the Seafloor Spreading Theory.
  • 18. According to this theory, hot, less dense material from below the earth’s crust rises towards the surface at the mid-ocean ridge. This material flows sideways carrying the seafloor away from the ridge, and creates a crack in the crust. The magma flows out of the crack, cools down and becomes the new seafloor. Overtime, the new oceanic crust pushed the old oceanic crust far from the ridge. The process of seafloor spreading allowed the creation of new bodies of water.
  • 19. Diagram of Seafloor Spreading
  • 20. In the place where two oceanic plates collide or where an oceanic plate and a continental plate collide, a subduction zone occurs. As the new seafloor is formed at the mid-ocean ridge, the old seafloor farthest from the ridge is destroyed at the subduction zone. The rate of formation of a new seafloor is not always as fast as the destruction of the old seafloor at the subduction zone.
  • 21. This explains why the Pacific Ocean is getting smaller and why the Atlantic Ocean is getting wider. If subduction is faster than seafloor spreading, the ocean shrinks. When the seafloor spreading is greater than the subduction, then the ocean gets wider.
  • 22. Findings that support Seafloor Spreading Theory: 1.Rocks are younger at the mid-ocean ridge. 2.Rocks far from the mid-ocean ridge are older. 3.Sediments are thinner at the ridge. 4.Rocks at the ocean floor are younger than those at the continents.
  • 23. 7. Magnetic Reversal The Earth’s magnetic field is generated in the very hot molten outer core and has already existed since the birth of our planet. The Earth’s magnetic field is a dipole, one that has a North Pole and a South Pole.
  • 25. Magnetic reversal is also called magnetic ‘flip’ of the Earth. It happens when the North Pole is transformed into a South Pole and the South Pole becomes the North Pole. This is due to the change in the direction of flow in the outer core.
  • 26.  Magnetic reversals happened many times in the past. The occurrence of magnetic reversals can be explained through the magnetic patterns in magnetic rocks, especially those found in the ocean floor. When lava solidifies, iron bearing minerals crystallize. As these crystallize, the minerals behave like tiny compasses and align with the Earth’s magnetic field. So when magnetic reversal occurs, there is also a change in the polarity of the rocks. This allowed scientists to visualize the magnetic stripes in the ocean floor.

Editor's Notes

  1. The convection currents rotate very slowly, as they move and drag the plates along. Because of convection current, the tectonic plates are able to move slowly along tectonic boundaries, pushing each other, sliding past each other and drifting away from each other. Aside from mantle convection, ridge push, sliding, and slab pull are other forces that move the lithospheric plates. As an oceanic crust moves away from a divergent boundary, it becomes denser than the newer oceanic crust. As the older seafloor sinks, the weight of the uplifted ridge pushes the oceanic crust toward the trench at the subduction zone. This process is called ridge push. Slab pull is the other possible process involved in the tectonic plate movement. The weight of the subducting plate pulls down the trailing slab into subduction zone. The convection current moves partially molten rock material (magma) upward to the crust where it cools, becomes cooler and sinks near the outer core where it is once again heated and becomes lighter thus rising again. This continuous rising and sinking motion of magma or convection current is the cause of the many tectonic activities such as plate boundaries, earthquakes, volcanoes and many others.
  2. You have learned from your previous lessons that lithospheric plates or the solid part of the Earth are gradually moving to form different geologic events such as earthquakes, mountain buildings, and volcanoes. But what causes these plates to move? What is the evidence that the Earth's Plates are moving? These questions ignited our scientists' curiosity to look for answers and lead to the development of the following ideas: Continental Drift Theory, Seafloor Spreading, and Earth's Magnetic Reversal.
  3. Look at the world MAP…Did you notice that the eastern border of South America and the Western part of Africa seem to fit together like a big jigsaw puzzle? But who is behind the discovery of the different evidences and theories on the plate movements…
  4. The next slide shows how Pangaea evolved into how the continents look today.
  5. The figure shows the evolution of the supercontinent Pangaea to the present-day distribution of continents., Wegener's curiosity about the idea of drifting continents started when he noticed the edges of South America and Africa in a World Map could be fitted like a jigsaw puzzle. Can you say that continents are drifting?
  6. His evidences to the Continental Drift Theory includes the distribution of fossils in different continents, rock features, and ancient climates. Is this idea somehow true? If you lived during Wegener’s time, will you believe him? Would fitting edges of continents be enough proof that the continents are drifting? What are the other pieces of evidence gathered by Wegener to support his Continental Drift Theory?
  7. Did it really start as one big landmass? It seems very impossible that the seven continents, which are currently thousands of miles away from each other were actually connected pieces of a supercontinent The evolution of the seven (7) continents and the five (5) oceans ASIA,AFRICA,EUROPE,NORTH AMERICA,SOUTH AMERICA,AUSTRIALIA (OCEANIA),ANTARCTICA…. 5 oceans …PACIFIC,ATLANTIC,INDIAN,ARCTIC,SOUTHERN
  8. Could it be possible that they existed in this region where temperature was very low? Or could it be possible that, long before, Antarctica was not in its current position?
  9. Fossils found in rocks support the Continental Drift Theory Q: How come these rock layers in different continents line up together with layers that exactly matched?
  10. Q: How is a coal bed formation possible in Antarctica?
  11. The question as to how the drifting took place left the Continental Drift Theory blurry. Despite the evidences presented by Wegener, his idea that the continents were once joined together was not accepted by the scientific society until the 1960s. He wasn’t able to explain how this drifting took place. This made scientists conduct further studies in search for the answer
  12. Seafloor spreading was strengthened with the discovery that the magnetic rocks near the ridge follow a pattern aside from the fact that rocks near the ridge are remarkably younger than those father from the ridge. A magnetic compass tells us directions on Earth. It also proves that the Earth has a magnetic field. The needle of a magnetic compass usually points to the North Pole of the Earth which is actually the South Magnetic Pole at present What is magnetic reversal? How does magnetic reversal happen and how does it prove seafloor spreading?