Geo_Lo3_earth_interior_contet_and layers.pptx

Geo LO3 for grade 12 STEM.

1. Made by : Group 2 Under Supervision of : Ms.Manal LO-3

2. Continental Drift Theory 01 Wagner’s Theory

3. Continental Drift Theory Alfred Wegener outlined Wegener’s hypothesis, called continental drift, which dared to challenge the long-held assumption that the continents and ocean basins had fixed geographic positions. Wegener suggested that a single supercontinent consisting of all Earth’s landmasses once existed. He named this giant landmass Pangaea.

4. Continental Drift Theory About 200 million years ago, during a time period called the Mesozoic era, this supercontinent began to fragment and “drifted” to their present positions over a span of millions of years. The fit of South America and Africa and the geographic distribution of fossils and ancient climates all seemed to buttress the idea that these now separate landmasses had once been joined.

5. Continental Drift Theory # One of the main objections to Wegener’s hypothesis stemmed from his inability to identify a credible mechanism for continental drift. Wegener proposed that gravitational forces of the Moon and Sun that produce Earth’s tides were also capable of gradually moving the continents across the globe. However, the prominent physicist Harold Jeffreys correctly argued that tidal forces strong enough to move Earth’s continents would have resulted in halting our planet’s rotation, which, of course, has not happened.

6. Continental Drift Theory Wegener’s drift hypothesis was correct, some details were incorrect. For example, continents do not break through the ocean, as he incorrectly suggested that the larger and sturdier continents broke through thinner oceanic crust, much as icebreakers cut through ice. However, no evidence existed to suggest that the ocean floor was weak enough to permit passage of the continents

7. 2. Density in Earth Interior

8. Density in Earth Interior Density refers to how concentrated the mass (atoms and molecules) in an object. Rocks in Earth’s crust are less dense than the rocks of the underlying mantle, so crust “floats” on the denser interior material. The weight of the overlying rock applies a force on the rock below, making it denser (due to pressure) The densest material should be at the center of Earth, where the pressure is greatest.

9. Density in Earth Interior Several kinds of evidence reveal that density varies within Earth. Laboratory experiments in high-pressure apparatuses show that rocks deep in Earth are denser than the same rocks when they are at the surface. The weight of the overlying rock applies a force on have separated because of their different densities. A second evidence comes from the average density of Earth by using Newton’s law of universal gravitation: every object in the universe attracts every other object with a gravitational force (F). This force is directly proportional to the product of their masses. The force is inversely proportional to the square of the distance between their centers of the masses). F .    

10. Density in Earth Interior Earth exerts a certain force on a body (like yours) with a certain mass (m1) on Earth’s surface. The surface of Earth is some 6400 km from its center. You can substitute these known values into the equation and calculate the mass of Earth (m2). Dividing the mass of Earth by its volume gives an average density of Earth (in metric units) of 5.5 g/cm3.  

11. Density in Earth Interior Earth Layers densities: Surface rocks: 2.8 g/cm3 (granite, basalt, and sandstone). Ocean surface rocks: 3 to 3.3 g/cm3 Mantle: 3.4 to 9.9 g/cm3 Outer Core: 10 g/cm3 Inner Core: 14 g/cm3 The density of Earth’s interior must be much greater than 2.8 g/cm3 for the entire Earth to average 5.5 g/cm3. This is partly due to the effect of compression. However, it is also partly because the material in Earth’s core is mostly iron (much denser than rocks, even when it is not under great pressure).  

12. 3. Flow of matter and Energy within Earth

13. Flow of matter and Energy within Earth The temperature of Earth increases with depth. At a depth of about 3.5 km below Earth’s surface, the temperature of a mine can reach 55°C. One of the sources of Earth’s internal heat is the decay of radioactive elements. Radioactive decay is the process by which an unstable nucleus of an atom gives off energy. Other sources of Earth’s internal heat include the original heat of Earth’s formation and heating by the impact of meteorites early. Earth can be thought of as a massive heat engine. The transfer of heat from Earth’s interior to its surface drives the movements of Earth’s crust and mantle. Temperature affects the density of materials. When the air inside a balloon is heated it expands (increases in volume), so density decreases (as mass is constant) and it begins to rise in air.

14. Flow of matter and Energy within Earth The less dense rock rises slowly over time, unless the rocks are too rigid to allow flow . They rise by thermal convection: a pattern of movement in a fluid caused by heating from below and cooling from above , then it becomes more dense and sinks back to bottom of the container. It transfers heat energy from one place to another by the movement of material. In 1929, Arthur Holmes proposed the idea that there were convection cells in Earth’s mantle which would be important in the development of the plate tectonic theory. He suggested that this thermal convection is like a conveyor belt. He reasoned that rising mantle material can break a continent apart which then forces the two parts of the broken continent in opposite directions(carry the continents).

15. Flow of matter and Energy within Earth Geologists are sure that the mantle is convecting . However, they are still unsure of the patterns of convection, as it cannot be observed directly. Geologists now think that the lithospheric plates are not just passive riders on the convection cells. Instead, the plates play a major part in driving the convection.   Mid-ocean ridges slope gradually down to the deep ocean nearer to the continents. The plates on either side of the ridge crest slope downward away from the ridge crest under the pull of gravity, so they help the convection cell to keep moving.

16. Flow of matter and Energy within Earth The plates in the ocean are denser than the deeper mantle. They have almost the same composition, but they are not as hot. They sink into the mantle by gravity, so they help to keep the convection cell moving. Summary of this hypothesis: material is heated at the core-mantle boundary. It rises upward and spreads out horizontally. The material cools and sinks back into the interior. These convection cells are very slow moving. Material rises to surface at places where the plates spread apart. Material sinks back into Earth where plates converge.

17. Any Questions?