Earth Processes

1. Earth Processes

2. How do Earth processes affect our everyday lives? Natural events such as volcanic eruptions, earthquakes, landslides, floods and gigantic sea waves make headlines and affect many people in obvious ways.

3. Affects Although we cannot prevent most of these natural disasters from happening, the more knowledge we have about what causes them, the better we will be able to predict, and possibly control the severity of impact.

4. Geologists Scottish geologist James Hutton, the eighteenth-century geologist developed the theory of uniformitarianism. English geologist Sir Charles Lyell is given the most credit for advancing the basic principles of modern geology.

5. The Rock Cycle Some people believe that "once a rock, always that rock".  But that is not always true.  Rocks take different forms at different times.  A long time ago our earth was very volcanic.  As these volcanoes cooled and vast oceans swept over the earth, the cooled lava was broken or crushed into small pieces.  These small pieces were cemented together to become sedimentary rocks. 

6. Rock Cycle contd. These rocks were buried and the heat and pressure changed them into metamorphic rocks.  They might even have melted and become igneous rocks once more.  As you can tell, a rock may change many times and the rock you hold today may look entirely different to someone a long time from now.

8. The Rock Cycle

10. Convection The mobile rock beneath the rigid plates is believed to be moving in a circular manner somewhat like a pot of thick soup when heated to boiling. The heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again. This cycle is repeated over and over to generate what scientists call a convection cell or convective flow.

11. Convection contd. While convective flow can be observed easily in a pot of boiling soup, the idea of such a process stirring up the Earth's interior is much more difficult to grasp. While we know that convective motion in the Earth is much, much slower than that of boiling soup, many unanswered questions remain: How many convection cells exist? Where and how do they originate? What is their structure?

12. Convection

13. Ancestor Rock Types Igneous Metamorphic Sedimentary

14. Igneous Igneous rocks, also called volcanic rocks, are formed from melted rock that has cooled and solidified. When rocks are buried deep within the Earth, they melt because of the high pressure and temperature; the molten rock (called magma) can then flow upward or even be erupted from a volcano onto the Earth's surface. When magma cools slowly, usually at depths of thousands of feet, crystals grow from the molten liquid, and a coarse-grained rock forms.

15. Igneous contd. When magma cools rapidly, usually at or near the Earth's surface, the crystals are extremely small, and a fine-grained rock results. A wide variety of rocks are formed by different cooling rates and different chemical compositions of the original magma. Obsidian (volcanic glass), granite, basalt, and andesite are four of the many types of igneous rock.

16. Sedimentary Sedimentaryrocks are formed at the surface of the Earth, either in water or on land. They are layered accumulations of sediments: fragments of rocks, minerals, or animal or plant material. Temperatures and pressures are low at the Earth's surface, and sedimentary rocks show this fact by their appearance and the minerals they contain. Most sedimentary rocks become cemented together by minerals and chemicals or are held together by electrical attraction; some, however, remain loose and unconsolidated.

17. Sedimentary contd. The layers are normally parallel or nearly parallel to the Earth's surface; if they are at high angles to the surface or are twisted or broken, some kind of Earth movement has occurred since the rock was formed. Sedimentary rocks are forming around us all the time. Sand and gravel on beaches or in river bars look like the sandstone and conglomerate they will become. Compacted and dried mud flats harden into shale. Scuba divers who have seen mud and shells settling on the floors of lagoons find it easy to understand how sedimentary rocks form.

18. Metamorphic Sometimes sedimentary and igneous rocks are subjected to pressures so intense or heat so high that they are completely changed. They become metamorphic rocks, which form while deeply buried within the Earth's crust. The process of metamorphism does not melt the rocks, but instead transforms them into denser, more compact rocks. New minerals are created either by rearrangement of mineral components or by reactions with fluids that enter the rocks.

19. Metamorphic contd. Some kinds of metamorphic rocks--granite gneiss and biotite schist are two examples--are strongly banded or foliated. (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Pressure or temperature can even change previously metamorphosed rocks into new types.

20. Earth Composition The Earth is not just a ball of solid rock. It is made of several layers with different physical properties and compositions. Scientists think about the Earth’s layers in two ways; by their composition and physical properties.

21. Earth’s CompositionThe Earth is divided into three layers • Crust- is the outermost layer ranging from 5-100 km thick. Is the thinnest layer and the most is known about this layer. • Mantle- is the layer between the crust and the core. It is thick and contains most of the Earth’s mass. • Core- believed to be made mostly of iron, nickle, sulphur and oxygen.

22. Earth’s Crust There are two types of crust: • Continental crust- has a composition like granite with an average thickness of 30 km. • Oceanic crust- has a composition similar to basalt with a thickness of 5 – 8 km thick. Because basalt is denser than granite, oceanic crust is denser than continental crust.

24. PHYSICAL PROPERTIES • FIVE LAYERS

25. Five Layers • Lithosphere • Asthenosphere • Mesosphere • Outer Core • Inner Core

26. Mnemonics • Litho- meaning “rock”, the lithosphere is the Earth’s solid, rocky crust • Astheno- meaning ‘weak”, the asthenosphere is a layer of slowly flowing rock beneath the lithosphere • Meso- meaning “middle’, the mesosphere lies between the asthenosphere and outer core.

27. Earth Structure

28. Earth Structure

30. Brain Food The deepest hole ever drilled into the continental crust was in the Kola Peninsula, in Russia, in 1984. It was 12,226 m deep! It is very difficult to drill much deeper because the deeper you go, the hotter it gets. If you drill too deep, the hot rock flows around the drill bit, filling the hole faster than it can be drilled.

31. Earth Composition

32. Earth Composition Inner Core – a solid iron-rich zone having a radius of 756 miles. Outer Core – a molten metallic layer 1410 miles thick. Mantle – a solid rocky layer with a maximum thickness of 1789 miles. Crust – a relatively lighter outer skin that ranges from 3 to 25 miles thickness.

33. Asthenosphere A very important zone located within the mantle. The asthenosphere is located between 60 and 150 miles down and is a hot weak zone that is capable of gradual flow.

34. Lithosphere Situated above the asthenosphere, this zone includes the crust and uppermost mantle. It can be considered cool and rigid. The lithosphere is approximately 60 miles thick.

35. Mapping the Interior How do we know these things about the Earth’s interior? Earthquakes produce seismic waves that can be measured. These seismic waves travel at different speeds through materials because of the difference in density of the material.

36. Speeds • Lithosphere- 7-8 km/sec • Asthenosphere- 7-11 km/sec • Mesosphere- 11-13 km/sec • Outer Core- 7-10 km/sec • Inner Core- 11-12 km/sec

37. Quiz • The crust is the Earth’s only solid layer. • The inner core of the Earth is solid and made primarily of iron. • Temperature and pressure increase toward the center of the Earth. • The asthenosphere is the thinnest.

38. Answers • False • True • True • False

39. Plate Tectonic Theory According to the plate tectonics model, The Earth’s rigid outer shell, the lithosphere, is broken into several individual pieces called platesthat move over the asthenosphere. Further, it is known that these rigid plates are slowly, but nevertheless continually moving.

40. Plate Tectonic Theory This motion is driven by a thermal engine, the result of an unequal distribution of heat within the Earth. As hot material gradually moves up from deep within the planet and spreads laterally, the plates are set in motion. Ultimately, this movement of Earth’s plates generates earthquakes, volcanic activity and mountain building.

41. Jigsaw Puzzle Look at the world map on the following slide and notice that each tectonic plate fits the other tectonic plates that surround it. The lithosphere is like a giant jigsaw puzzle. Also, notice that not all tectonic plates are the same. Compare the size and composition, some have both types of crust and some have only one type of crust.

43. Plate Close-Up From the previous slide, notice that this tectonic plate consists of both oceanic and continental crust. The thickest part is under the Andes mountains and the thinnest part is at the Mid-Atlantic Ridge.

44. Continental Drift • Geologist Alfred Wegener proposed the theory of continental drift. Simply stated, Earth’s land had once been joined into a single super continent surrounded by ocean. • Pangea- super continentland mass • Panthalassa- surrounding ocean

45. Continental Drift Theory The continental drift theory explained why the shorelines of different continents fit together like a puzzle, why the same fossil animals and plants are found on different continents and how different mountain ranges were once part of a larger continuous mountain range.

46. Plate Movement 200 mya 225 mya 135 mya 35 mya Present

48. Sea-Floor Spreading As rising material from the mantle spreads laterally, sea floor is carried in a conveyor belt fashion away from the ridge crest. Tears at the ridge crest produced by the diverging plate boundaries provide pathways for magma to intrude and generate new oceanic crust.

49. Sea-Floor Spreading Mid- Ocean ridges are places where sea-floor spreading takes place. Sea-floor spreading is the process by which new oceanic lithosphere is created as older material is pulled away. As tectonic plates pull away from each other, the sea floor spreads apart and magma rises to fill the gap.

50. Page 175, Figure 11 Notice that the crust increases with age the farther away from the mid-ocean ridge. This is because new crust continually forms from molten material at the ridge. The oldest crust in the Atlantic Ocean is found along the edges of the continents. It dates back to the time of the dinosaurs. The newest crust is in the center of the ocean.