Understanding Earth's Geologic Processes: Steno to Kelvin

1. Unit 10, Chapter 28 Integrated Science

2. 28.1 Understanding Earth • Geology is the study of rocks and materials that make up Earth and the processes that shape it. • In 1666, Nicholas Steno (1638-87) noticed that shark’s teeth resembled mysterious stones called “tonguestones” that were found in local rocks.

3. 28.1 Understanding Earth • Steno’s explanation helped him develop ideas about how rocks and fossils form. • These ideas are used in a technique called relative dating. • Relative dating is a way to put events in the order in which they happened. What happened here and in what order?

4. The approximate age of each layer of a rock formation can be determined by applying Steno’s idea called superposition. A stack of newspapers illustrates superposition. Superposition means that the bottom layers of rock are older than the layers on the top, unless they have been disturbed. 28.1 Understanding Earth

5. Original horizontalitystates that sediment particles fall to the bottom of a basin, such as a riverbed, in response to gravity and result in horizontal layers. 28.1 Understanding Earth

6. Lateral continuityis the idea that layers of sediment extend in all directions when they form and before they become rock layers. The idea of lateral continuity states that layers of rock are continuous unless a geologic event like a river interrupts the layers or an earthquake offsets them. 28.1 Understanding Earth

7. Another important idea, developed by Scottish geologist James Hutton (1726-97), is that the "present explains the past." The idea of cross-cutting relationshipsstates that a vein of rock is younger than the rock that surrounds the vein. 28.1 Understanding Earth vein

8. Sometimes rock pieces called inclusions are contained in another rock. During the formation of a rock with inclusions, sediments or melted rock surround the inclusion and then become solidified. Therefore, the inclusions are older than the surrounding rock. 28.1 Understanding Earth

9. Over geologic history, many animals and plants have lived and become extinct. Their remains have become fossils. The idea of faunal succession states that fossils can be used to identify the relative age of layers of a rock formation. 28.1 Understanding Earth

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11. William Thompson Kelvin (1824-1907), known for proposing the absolute temperature scale that came to be named after him, meticulously calculated Earth’s age to be between 10 million and 100 million years. Lord Kelvin’s calculation was not accurate because he did not realize that Earth has internal heat from the core and radioactive decay. 28.1 Calculating Earth's Age

12. Earth’s 3 “internal” heat sources • Original Heat – this is the left over heat of Earth’s creation from the bombardment of meteorites and asteroids. Only about 1% left • Friction between atoms – this heat is generated by gravity squeezing the Earth into its sphere shape. Accounts for about 40% of heat • Radioactive decay – the breakdown of radioactive isotopes like uranium provides the Earth with most of its internal heat, about 60%.

13. Today Earth’s age has been given by measuring the radioactive decay of uranium into lead. Absolute dating As techniques and evidence from tree rings and glaciers, and rock layers, improved Earth’s age has been determined to be about 4.6 billion years. 28.1 Calculating Earth's Age

15. Earth’s surface is covered with a thin crust. There are two kinds of crust: continental oceanic 28.1 The Layers of the Earth

17. The rocky material of the mantle moves in very slow convection currents. This movement is related to density and temperature differences in the mantle. Hot material is less dense and rises. Cold material is denser and sinks. 28.1 Convection inside Earth

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21. In 1915, Alfred Wegener (1880-1930), a German meteorologist, wrote a book titled The Origin of Continents and Oceans. 28.2 Continental Drift • Wegener gathered evidence that supported his idea that all the continents had been connected.

22. Continental Drift • The apparent movement of the continents relative to one another over the Earth’s crust.

23. 1st evidence:   Fit of the continents. • He cut out and pieced together a crude map. • He called the great ocean Panthalassa (meaning all seas) • The continent was called Pangaea (meaning all lands)

24. 2nd body of evidence: Matching rocks:Found on these continents. • 1. North Eastern N. America & Western Europe. • 2. Southern N. America & North Africa. • 3. South America & Africa. • 4. Not enough proof!!

25. 3rd body of evidence Identical fossils found all over the world: • 1. East South America & West Africa. • 2.  Southern North America & Northern Africa. • 3. Northern North America and Europe.

26. pangaea animation

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28. Theory of plate tectonics, started in 1965, and explains the movement of continents and other geological events, like earthquakes and volcanoes through the movement of giant plates of rock called tectonic plates. Tectonics means construction or building. 28.2 Plate Tectonics

29. In the early 1960s, Henry Hess (1906-69), a geologist and former commander of a Navy ship equipped with an echo sounder, used the profile of the sea floor to propose that it was spreading at the mid-ocean ridges. 28.2 Sea Floor Spreading • An echo sounder is used to make a profile of the sea floor.

30. At the same time, Robert Dietz (1914-95), a scientist with similar ideas, coined the term sea-floor spreading. Sea-floor spreading says the sea floor on either side of a mid-ocean ridge is moving away from the ridge and creating a rise or valley. 28.2 Sea Floor Spreading

31. Magma from the mantle enters the rise or valley and cools, creating new oceanic crust). 28.2 Sea Floor Spreading

32. 28.2 Magnetic Patterns • Over eons themagnetic polarity of Earth switches, (North South) • Scientists believe the poles switch because of a magnetic interaction between the planet’s inner and outer core. • In the 1950s and 1960s, scientists discovered that the rocks of the sea floor have a very interesting magnetic pattern.

33. 28.2 Magnetic Patterns • Stripes of rock with a north-south orientation (normal) alternate with stripes of rock with a south-north orientation (reversed). • This striping tells us 7 important things.

34. 28.2 Magnetic Patterns • First, it tells us the Earth’s magnetic field changes about every 100,000 years. • Second, it tells us the ocean crust is being constantly recycled • Third, it tells us the newest crust is at the center of the ridge or rise. • Forth, it tells us the most heat is being released from the Earth’s interior at the center of the ridge or rise. • Fifth, it tells us the direction the convection currents move, under those plates • Sixth, it tells us the speed of the convection currents. • Seventh, it tells us if new plate is being created here, the oldest ocean crust must be being destroyed somewhere.

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37. There are three main kinds of plate boundaries: divergent convergent transform 28.2 Describing Plate Boundaries

38. Tectonic plates are pieces of lithosphere that fit together and “float” on the asthenosphere. There are a number of large tectonic plates on Earth’s surface, and many smaller plates are being identified all the time. 28.2 Plate Tectonics

39. Can you identify which of the plates are only made of oceanic crust?

40. Section 28.2 Plate Boundaries Divergent Boundary– where 2 plates are pulled apart. In this picture 2 ocean crusts. • Here hot less dense magma rises up through the asthenosphere toward surface, causing the convection currents, & undersea EQs • MID-OCEAN RIDGE -string of undersea divergent boundaries where new ocean crust is formed. • Called spreading centers & are associated with mountainous areas on ocean floor • Earthquakes, volcanoes, rifts common

41. Diverging plates move apart and new crust forms. 28.2 Divergent Plate Boundaries

42. Divergent boundaries are sites of earthquakes and volcanic activity. Mid-ocean ridges and associated sea-floor spreading occur at divergent plate boundaries. In effect, a mid-ocean ridge is like a very long volcano. 28.2 Divergent Plate Boundaries

43. Plate Boundaries Convergent • Where 2 plates collide by moving together. • SUBDUCTION ZONE area where an ocean plate dives or sinks under another ocean plate, or continental plate. • Old crust is subducted and destroyed here. Dives into the Asthenosphere, melts then rises and circulates again. • Volcanic islands & trenches are the most common landforms. EQ of all depths occurs • Volcanoes common This is 2 Ocean crusts.

44. Plate Boundaries Convergent • This is an oceanic and continental plate subduction zone. • The plates move toward each other. • Volcanoes & trenches are most common landforms. • Magma is generated at all subduction zones where dense oceanic plates are pushed under lighter continental plates, melted, and rises back up through the crust. • Shallow, intermediate and deep EQ, volcanoes occur

45. Plate Boundaries • This convergent boundary is where 2 continental crusts collide. • The rock layers are folded and bent forming mountains. • The plates move toward each other. • Mountains and Valleys are the common land forms • Volcanoes rare

47. Convergent plate boundaries occur where two plates approach each other. One result of two plates converging is subduction. A deep oceanic trench marks the boundary between a subducting and an overriding plate at a convergent boundary. 28.2 Convergent Plate Boundaries

48. Plate Boundaries Transform

49. Plate Boundaries Transform • This boundary is a lateral boundary where two plates slide past each other. • Earthquakes occur frequently at these boundaries. • The plates can move in same direction but at different rates. Many rolling hills and shallow trenches are common. • ANY TYPE OF CRUST, transform is most common on earth.