ES 16 Historical Geology Spring 2009

1. ES 16 Historical Geology Spring 2009

2. Spheres of the Earth • When we view the Earth from space what Earth systems are observable? • What is most obvious? • Are these systems independent or do they interact with one another?

4. Spheres of the Earth • Lithosphere: Earth’s solid rocky mass • Hydrosphere: All of earth’s water • Atmosphere: The thin gaseous layer above Earth’s surface • Biosphere: All of earth’s life forms

5. Atmosphere Biosphere Gasesfrom respiration Transport of seeds and spores

6. Wind erosion, transport of water vapor for precipitation Mountainsdivert air movements Atmosphere Lithosphere

7. Source of sediment and dissolved material Water and glacial erosion, solution of minerals Hydrosphere Lithosphere

8. Historical Geology: A study of the dynamic and evolving Earth • Changes in its surface • Changes in life

9. Three Themes dominate the story of the evolving Earth • Solid Earth is composed of plates that move over Earth’s surface over time. This is explained by the Theory of Plate Tectonics • Earth’s biota – all of living things – has evolved or changed through history and is explained by the Theory of Organic Evolution • All of the geologic processes take place within an extensive geologic time scale spanning 4.6 billion years of Earth’s history

10. Historical Geologyapplies geologic principles to help explain processes on Earth from past to present • William Smith was an English surveyor who realized that rock types and fossils occur in repeated patterns. He was able to predict rock sequences that would be encountered in constructing canals • Smith mapped the geology of much of England. (1815)

11. This map took many years to complete and helped establish the geologic time scale.

12. Hypothesis or Theory? • The scientific method brings an orderly and logical approach to decoding geologic evidence. • A hypothesis is a tentative explanation for observations • Scientists make predictions using hypotheses – then they are tested • After repeated testing, a theory may be proposed • Some phenomena cannot be tested or explained • Some are discovered by sheer chance!

13. A theory is formed • A theory is more than an “educated guess” • A theoryexplainsnatural phenomena and may relate several observations • A theory is well-tested,well-supported and widely accepted. • Examples include the Plate Tectonics Theory and the Theory of Organic Evolution

14. Where do scientists look for evidence for the following? • The origin and age of the universe • The origin and age of the solar system • The origin and age of the Earth and Moon • The origin of life on Earth • Evidence of plate movement on Earth • Explanation for large scale extinctions on Earth

15. How old is the universe? • When? Scientists believe the universe was formed about 15 billion years ago • How?The Big Bang is a model for the “beginning” of the universe • “Show me”! What is the evidence?

16. Edwin Hubble and Albert Einstein: contemporaries in time and space

17. Birth of a modern hypothesis • Hubble, an Oxford Rhodes scholar, a former lawyer, and boxer, with a PhD in astronomy, was an infantry soldier in WW I. • After the war he went to work at Mt. Wilson observatory using the 100” Hooker Telescope. • Here he observed the existence of galaxiesoutside of theMilky Way

18. A new view of the Universe • Hubble used light, which travels over finite time from one part of the universe to another, to measure distance to stars outside of the Milky Way. • By studying variable stars with predictable cycles, he discovered that objects are moving uniformly away from our Galaxy • He used the red shift of stellar spectra to measure distances and velocities of deep space objects • Hubble concluded that the universe is expanding and that distant stars and galaxies are moving away from the Milky Way.

19. A few years earlier, Einstein had predicted the universe would be found to be expanding. • He proposed his theory of relativity and proposed that the objects in the universe are not moving apart; rather space is expanding and the objects are carried along The effects of gravity on light

20. Hubble’s Constant quantifies the movementUsing predictable variable stars, along with redshift observations, Hubble predicted that a galaxy twice as far away from us is receding twice as fast. • This was predicted by Einstein’s theory of relativity. Hubble’s constant was tested and continues to be refined today as the ability to observe the outer reaches of the universe improves.

21. So………. • The universe is expanding • Think of a deflated balloon with markings on it, • Being blown up • Causing the markings to move apart.

22. Other evidence of the Big Bang • Pervasive background radiation of 2.7o above absolute zero is observed in space --Afterglow of the Big Bang To Find the Age of the Universe: • Determine rate of expansion • Backmodel to a time when the galaxies would be together in space

23. Big Bang hypothesis • Initial state: NO time, NO matter, NO space • Universe was pure ENERGY • During the FIRST second of time: --very dense matter came into existence --The four basic forces separated: gravity, electromagnetic force, strong and weak nuclear forces --Enormous expansion occurred

24. Big Bang Model • 300,000 years later: • Atoms of hydrogen and helium formed • Light (photons) burst forth for the first time • Next 200 million years: • Continued expansion • Stars and galaxies began to form • Elements heavier than hydrogen and helium began to form with stars by nuclear fusion

25. Origin of Our Solar System Solar nebula theory • cloud of gases and dust • formed a rotating disk • condensed and collapsed due to gravity • forming solar nebula • with an embryonic Sun • surrounded by a rotating cloud

26. Embryonic Sun and Rotating Cloud • Planetesimals have formed • in the inner solar system, • and large eddies of gas and dust • remain far from the protosun

27. Terrestrial Mercury Venus Earth Mars Small in size. Composed of rock. Metallic cores. Asteroid Belt Jovian Jupiter Saturn Uranus Neptune Large in size. Composed of hydrogen, helium, ammonia, methane Small rocky cores Pluto ????????? The Planets

29. The sun is believed To be about 5 billion years old – about half way through its life cycle.

30. Earth’s Very Early History • Started out cool about 4.6 billion years ago • probably with uniform composition/density • Mostly: • silicate compounds • iron and magnesium oxides • Temperature increased. Heat sources: • meteorite impacts • gravitational compression • radioactive decay • Heated up enough to melt iron and nickel

32. Earth’s Differentiation • Differentiation = segregated into layers of differing composition and density • Early Earth was probably uniform • Molten iron and nickel sank to form the core • Lighter silicates flowed up to form mantle and crust

33. Forming the Earth-Moon System • Impact by Mars-sized planetesimal with early Earth • 4.6 to 4.4 billion years ago • Ejected large quantity of hot material • Formed the moon

34. Most of the lunar material Came from the mantle of the colliding planetesimal The material cooled and Crystallized into lunar layers Light colored surface areas are lunar Highlands – heavily cratered. Evidence of massive meteorite Bombardment Mare are areas of lava flows

35. Earth—Dynamic Planet • Earth was also subjected • to the same meteorite barrage • that pock-marked the Moon • Why isn’t Earth’s surface also densely cratered? • Because Earth is a dynamic and evolving planet • Craters have long since been worn away

36. Earth’s Interior Layers • Crust - 5-90 km thick • continental and oceanic • Mantle • composed largely of peridotite • dark, dense igneous rock • rich in iron and magnesium • Core • iron and a small amount of nickel

37. Earth’s Interior Layers • Lithosphere • solid upper mantle and crust • Crust - 5-90 km thick • continental and oceanic • Mantle • composed largely of peridotite • dark, dense igneous rock • rich in iron and magnesium • Asthenosphere • part of upper mantle • behaves plastically and slowly flows • Core • iron and a small amount of nickel

38. Earth’s Interior Layers • Lithosphere • solid upper mantle and crust • broken into platesthat move over the asthenosphere • Asthenosphere • part of upper mantle • behaves plastically and slowly flows

39. Earth’s Crust • outermost layer • continental (20-90 km thick) • density 2.7 g/cm3 • contains Si, Al • oceanic (5-10 km thick) • density 3.0 g/cm3 • composed of basalt

40. Plate Tectonic Theory • Lithosphere is broken into individual pieces called plates • Plates move over the asthenosphere • as a result of underlying convection cells

41. Continental-continental convergent plate boundary Divergent plate boundary Continental-oceanic convergent plate boundary Oceanic-oceanic convergent plate boundary Divergent plate boundary Mid-oceanic ridge Trench Plate Tectonic Theory:A Revolutionary Concept! • Types of plate boundaries Transform plate boundary

42. Modern Plate Map

43. Plate Tectonic Theory • A major Breakthrough in the 1960s: • comparable to Darwin’s theory of evolution in biology • Explains and provides a working framework for • interpreting many processes on Earth on a global scale • relating many seemingly unrelated phenomena • interpreting Earth history

44. Theory of Organic Evolution Provides a framework • for understanding the history of life • Darwin’s • On the Origin of Species by Means of Natural Selection, published in 1859, • revolutionized biology

45. Central Thesis of Evolution • All present-day organisms • are related • and descended from organisms • that lived during the past • Natural selection is the mechanism • that accounts for evolution • Natural selection results in the survival • to reproductive age of those organisms • best adapted to their environment

46. History of Life • The fossil record provides perhaps • the most compelling evidence • in favor of evolution • Fossils are the remains or traces • of once-living organisms • Fossils demonstrate that Earth • has a long history of life

47. Geologic Time • From the human perspective time units are in • seconds, hours, days, years • Ancient human history • hundreds or even thousands of years • Geologic history • millions, hundreds of millions, billions of years

48. Geologic Time Scale • Resulted from the work of many 19th century geologists who • pieced together information • from numerous rock exposures, • constructed a sequential chronology • based on changes in Earth’s biota through time • The time scale was later dated in years • using radiometric dating techniques

49. Geologic Time Scale

50. Principle of Uniformitarianism:The Present is the key to the past • Uniformitarianismis a cornerstone of geology • is based on the premise that present-day processes • have operated throughout geologic time • The physical and chemical laws of nature • have remained the same through time • To interpret geologic events • from evidence preserved in rocks • we must first understand present-day processes • and their results • Rates and intensities of geologic processes • may have changed with time