Chapter 1: Meet Planet Earth

1. Chapter 1: Meet Planet Earth

2. Introduction • No other planet in the solar system currently has the right chemical and physical mix needed to support life. • No conclusive evidence of life existing elsewhere in the universe has yet been discovered as far as we know. • Earth is unique.

3. Human Influences • We human are influencing Earth’s external geologic processes. • More than 6 billion people.

4. Human Influences (2) • Our daily activities are having measurable effects on: • Rainfall. • Climate. • Air. • Water quality. • Erosion. • In North America, we use 20 tons of mineral resources per person/year.

5. Geology • Geology is the science of Earth. • Geologists study the Earth’s processes, such as: • Volcanism. • Glaciation. • Stream-flow. • Rock formation.

6. Geologists Also Study : • Chemistry, to understand: • Minerals. • Dissolved minerals. • Minerals resources. • Rocks formation. • Ground water.

7. Geologists Also Study :(2) • Physics, to understand: • Plate tectonics. • Volcanism. • Earthquakes. • Landslides. • Biology, to understand: • How life processes integrate with other Earth systems. • How life has evolved. • Fossils in the rocks.

8. Geologists Also Study : (3) • Meteorology, to understand: • Stream flow. • Groundwater levels. • Oceanography, to understand: • Seafloor’s role in plate tectonics. • Shorelines.

9. Geologists Also Study : (4) • Astronomy. • Mathematics. • Computer sciences. • Economics, to understand how humans employ: • Minerals. • Energy resources.

10. What Do Geologists Do ? • They seek to understand all processes that operate on and inside the Earth. • They study: • Our planet’s long history. • Water bodies (rivers and lakes). • Hazardous processes such as earthquakes, volcanic eruptions, flood, and landslides. • Rocks. • Spot surface patterns. • They use ground-penetrating radar.

11. Physical Versus Historical Geology • Historical geology • Chronology of events, both physical and biological, that have occurred in the past. • The past is the biggest clue to the present. • Physical geology • Concerned with understanding the processes and the materials.

12. Plate tectonics. Volcanism. Earthquakes. Landslides. Floods. Formation of mineral deposits. Mountain-building. Shore erosion. Landscape formation. Rocks. Minerals. Air. Seawater. Soil. Sand Physical Geology Also Studies

13. The Scientific Method (1) • Geologists use a research strategy called the scientific method. • The scientific method includes the following steps: • Observe and measure. • Form a hypothesis (a plausible, but unproved, explanation for the way something happens).

14. The Scientific Method (2) • Test the hypothesis (by comparing the predictions against the new observations). • Formulate a theory (a generalization about natural phenomena). • Formulate a law or principle (statements that some natural phenomenon is invariably observed to happen in the same way, and no deviations have ever been observed). • Continually reexamine the law or principle in the light of new evidence.

15. How Rapid Are Geologic Processes? • During the seventeenth and eighteenth centuries, people believed that Earth’s features (mountains, valleys, oceans, rivers) were permanent and had been produced by a few great upheavals. • This theory is called Catastrophism.

16. James Hutton Applies the Scientific Method • James Hutton (1726-1797), now known as the father of modern scientific geology, assembled evidence and proposed a counterhypothesis called gradualism. • In 1795, he published “Theory of the Earth with Proofs and Illustrations.” • He proposed uniformitarianism, which asserts that everything must move slowly in a repetitive, continuous cycle.

17. Uniformitarianism • States that the same processes we observe today have been operating throughout Earth’s history. • The cycle of uplift, erosion, transport, deposition, solidification into rock, and renewed uplift requires a great deal of time for its operation. • The Earth is 4.55 billion years old.

18. Catastrophism • Recently, a thin and very unusual rock layer, rich in the rare metal iridium, has been discovered at many locations worldwide. • It indicates that a catastrophic impact from a meteor may have occurred about 66 million years ago. • The mass extinction of dinosaurs occurred at that time. • More dramatic extinctions have occurred at other times in the past. • The mass extinction occurring about 245 million years ago eliminated almost 90 percent of all plants and animals living at the time. • Events such as earthquakes, volcanic eruptions, tsunami, floods, and landslides are local catastrophes.

19. Geologic Time and Earth’s Age • Stratigraphy is the study of the structure of sedimentary layers recording a sequence of past events. • The layers at the bottom of the pile are the oldest. • Those at the top are the youngest. • Stratigraphy identifies the relative age of many geologic events. • Relative age identifies position in a limited sequence. (“This is older than that.”) • Radioactivity can be used to establish the absolute age of geologic events. • Absolute age identifies position in a universal sequence (such as our current system of naming years in chronological order). (“This is 49,000 years old.”)

20. Geologic Time and Earth’s Age • The Appalachians rose about 300 million years ago. • The modern Rockies about 70 million years. • The most recent great ice sheets retreated about 12,000 years ago.

21. The Solar System • Earth is part of the solar system. • Solar system consists of: • The sun. • Nine planets. • Over five dozen moons. • Vast numbers of asteroids. • Millions of comets. • Innumerable small fragments of rock and dust called meteoroids.

22. Figure 1.9 A

23. Figure 1.9 B

24. The Planets • The solar system’s nine planets can be divided into two groups: • The terrestrial planets: Mercury, Venus, Earth, Mars. • Closest to the sun. • Small, rocky, and dense (3g/cm3 or greater). • The Jovian planets: Jupiter, Saturn, Uranus, Neptune, Pluto. • Farther from the sun than Mars. • Much larger than the terrestrial planets. • Much less dense. • Pluto is a structural exception in the Jovian planets. • Is it a planet or an asteroid?

25. Figure 1.7 a

26. Figure 1.7 b

27. More on the Jovian Planets • All of these planets are likely to have solid cores. • They consist largely of the very light elements and volatile substances: • hydrogen. • helium. • carbon dioxide. • ammonia.

28. Origin of the Solar System and Earth • Birth began in a huge volume of space where earlier stars had exploded into supernovas, producing a swirling cloud of cosmic gas. • Over millions of years, gravity slowly gathered the thinly spread atoms into a thicker gas. • Near the center of this gathering cloud the temperature and density became so great that hydrogen atoms began to fuse to form helium atoms (a nuclear reactor). • The outer portion of the cosmic gas cloud cooled and became dense enough to allow solid objects to condense (planets, moons, and the other solid objects of the solar system).

29. Planet Temperature • Planets and moons nearest the sun (highest temperature) contain: • Compounds that condense only at high temperature (iron, silicon, magnesium, and aluminum), most bind strongly with oxygen. • Planets and moons more distant from the sun (lower temperature) contain: • Volatile substances (hydrogen and sulfur combined with oxygen). • Moons of Jupiter: • Io is red because it is rich in sulfur. • Europa, smallest of Jupiter’s four large moons, contains a substantial amount of ice.

30. Figure 1.10

31. Planetary Accretion and Meteorites • Meteorites and the scars of ancient impacts provide evidence of the way terrestrial planets grew to their present sizes. • This growth process is called planetary accretion. • Planetary accretion continues to happen today.

32. Earth’s Internal Structure • When a meteorite impacts a planet or moon, its energy of motion (called kinetic energy) is transformed into heat energy. • As Earth grew larger and larger from continual impacts, its temperature increased. • Radioactive decay of materials like uranium, thorium and potassium also added heat. • Because Earth became partly fluid, less-dense molten materials (silicon, aluminum, sodium, and potassium) were freed to migrate toward the surface. • Denser melted materials, such as molten iron, sank toward the center of the planet.

33. The Earth’s Interior • Planet Earth has three main parts: • At the center is the densest part, the core (metallic iron, nickel). • Surrounding the core is the mantle. • Surrounding the mantle lies the thinnest and outermost layer, the crust.

34. Figure 1.13

35. The Earth’s Crust • The crust is not uniform. • The oceanic crust on average is about 8 km thick. • The continental crust on average is about 45 km thick.

36. Investigating the Earth’s Interior • How do we know anything about the composition of the core and the mantle? • By measuring the time required for earthquake waves to travel through Earth by different paths, we can determine the composition of the materials through which they move. • Iron meteorites are believed to be fragments from the core of a small terrestrial planet that was shattered by a gigantic impact.

37. The Layers of the Earth’s Interior (1) • The inner core • Pressures are so great that iron is solid, despite its high temperature. • The outer core • Iron is molten and exists as a liquid. • The Mesosphere • The mantle between the bottom of the asthenosphere to the core-mantle boundary. • The temperature at the core-mantle boundary is about 50000C.

38. The Layer of the Earth’s Interior (2) • The Asthenosphere: • The region of the mantle where rocks become ductile, have little strength, and are easily deformed. It lies at a depth of 100 to 350 km below the surface. • The Lithosphere: • The outer 100 km of the solid Earth, where rocks are harder and more rigid than those in the plastic asthenosphere.

39. Plate Tectonics (1) • The Earth gets rid of heat and keeps a nearly constant internal temperature through convection in the mesosphere and asthenosphere. • Plate tectonics theory says that Earth’s outermost 100 km “eggshell” (the lithosphere) is cracked in about a dozen large pieces.

40. Plate Tectonics (2) • In the 1960s, research by many geologists and oceanographers melded into the revolutionary hypothesis of plate tectonics. • Plate tectonics is a group of processes by which large fragments (plates) of lithosphere move horizontally across the surface of the Earth. Through their movements and interactions, they generate: • Earthquakes. • Volcanism. • Mountain-building. • Other geologic processes.

41. The System Concept • A system in any portion of the universe that can be isolated from the rest of the universe for observing and measuring change. • The simplest kind to understand is an isolated system. • the boundary completely prevents the exchange of either matter or energy.

42. The System Concept (2) • The nearest thing to an isolated system in the real world is a closed system: • exchanges energy with its surroundings, but not matter. • An open system can exchange both energy and matter across its boundary.

43. Figure 1.14

44. Figure 1.15

45. The Earth System (1) • The Earth system is composed of: • The geosphere (rocks). • The atmosphere (air). • The hydrosphere (water). • The biosphere (life in all its forms). • Energy and materials (like water, carbon, and minerals) are transferred from one system to another. • To a close approximation, Earth is a closed system.

46. The Earth System (2) • Earth is only approximately a closed system because: • Meteorites do come in from space and fall on Earth. • A tiny trickle of gases leaves the atmosphere and escapes into space. • Earth is comprised of four open systems.

47. Our Planet’s “Four Spheres” • The atmosphere: • Nitrogen, oxygen, argon, carbon dioxide, and water vapor. • The hydrosphere: • Oceans, lakes, streams, underground water, snow, and ice. • The biosphere: • All of Earth’s organisms, as well as any organic matter not yet decomposed. • The geosphere: • The solid Earth from core to surface, composed principally of rock and regolith.

48. Figure 1.16

49. Cyclical Movements • The movement of materials is continuous. • There are two key aspects to cycles: • The reservoirs in which the materials reside. • The flows, or fluxes, of materials from reservoir to reservoir. • The speed of movement differs greatly in different cycles.

50. Figure 1.17