1. The Age of the Earth Prior to the 19th century, accepted age of Earth based on religious beliefs –~6,000 years for Western culture (Biblical) –Old beyond comprehension (Chinese/Hindu) James Hutton, the“father of geology”, realized geologic processes require vast amounts of time Charles Lyell popularized Hutton’s concepts in book Principles of Geology –Uniformitarianism/actualism: same processes operating in past are operating at present - “The present is the key to the past”

2. History of Early Geology Catastrophism (James Ussher, mid 1600s) - He interpreted the Bible to determine that the Earth was created at 4004 B.C. This was generally accepted by both the scientific and religious communities. Subsequent workers then developed the notion of catastrophism, which held that the Earth’s landforms were formed over very short periods of time. Uniformitarianism (James Hutton, late 1700s) - He proposed that the same processes that are at work today were at work in the past. Summarized by “The present is the key to the past.” Hutton, not constrained by the notion of a very young planet, recognized that time is the critical element to the formation of common geologic structures. Uniformitarianism is a basic foundation of modern geology.

3. Lifespan of a human~ 100 years Human civilization~10,000 years Modern humans~100,000 years Stone tools~1,000,000 years Age of oceanic crust~100,000,000 years Precambrian Explosion~540,000,000 years Oldest Rocks~3.8 Billion years Age of the Earth~4.3 Billion years Age of the Solar System~4.6 Billion years Age of the Universe~14 Billion years Geologic Time and Clocks

4. Relative vs. Numerical Age Relative age - the order of events or objects, from first (oldest) to last (youngest) –Determined by applying simple principles, including original horizontality, superposition, lateral continuity, cross-cutting relationships, inclusions, unconformities, and correlation of rock units and fossils Numerical age - the age of events or objects, expressed as a number or numbers –Determined using radiometric dating (determining how much radioactive decay of a specific element has occurred since a rock formed or an event occurred)

5. Absolute Ages Numerical dating - puts absolute values (e.g., millions of years) on the ages of rocks and geologic time periods –Uses radioactive decay of unstable isotopes –Only possible since radioactivity was discovered in 1896 –Radioactive isotopes decay in predictable manner, giving a characteristic half-life (time it takes for a given amount of radioactive isotope to be reduced by half)

6. N = N 0 e -kt Radioactive Decay Where N is the amount of the radioactive element in the rock now; N 0 is the amount originally in the rock, e ~ 2.718 (natural logarithm); k is the decay constant of the radioactive element, and t is time. Half-life when N/N 0 = 0.5

7. Absolute (Radiometric) Dating : Using radioactive decay of elements to determine the absolute age of rocks. This is done using igneous and metamorphic rocks. Absolute Time: Radiometric Clocks Carbon-14half-life ~ 5730 years Used in anthropology

8. Relative Age Determination Contacts - surfaces separating successive rock layers (beds) Formations - bodies of rock of considerable thickness with recognizable characteristics allowing them to be distinguished from adjacent rock layers Original horizontality - beds of sediment deposited in water are initially formed as horizontal or nearly horizontal layers

9. Relative Age Determination Superposition - within an undisturbed sequence of sedimentary or volcanic rocks, layers get younger from bottom to top Lateral continuity - original horizontal layer extends laterally until it tapers or thins at its edges

10. Which are the youngest rock layers? What is the sequence of formation?

11. Relative Age Determination Cross-cutting relationships - a disrupted pattern is older than the cause of the disruption –Intrusions and faults are younger than the rocks they cut through Baked contacts - contacts between igneous intrusions and surrounding rocks, where surrounding rocks have experienced contact metamorphism Inclusions - fragments embedded in host rock are older than the host rock

12. Which are the youngest rock layers? What is the sequence of formation?

13. Unconformities Unconformity - a surface (or contact) that represents a gap in the geologic record Disconformity - an unconformity in which the contact representing missing rock layers separates beds that are parallel to each other Angular unconformity - an unconformity in which the contact separates overlying younger layers from eroded tilted or folder layers

17. Unconformities Nonconformity - an unconformity in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock –Plutonic and metamorphic rocks exposed by large amounts of erosion –Typically represents a large gap in the geologic record

20. Which are the youngest rock layers? What is the sequence of formation? Where is the unconformity?

21. What is the sequence of events?

22. Correlation Correlation - determining the time-equivalency of rock units –Within a region, a continent, between continents Physical continuity –Physically tracing a continuous exposure of a rock unit –Easily done in Grand Canyon Similarity of rock types –Assumes similar sequences of rocks formed at same time –Can be inaccurate if very common rock types are involved Correlation by fossils –Fossil species succeed one another through the layers in a predictable order (faunal succession) –Similar fossil assemblages (groups of different fossil species) used

25. William Smith: father of stratigraphy

28. Smith’s Fossil Assemblages

30. Lithostratigraphy (correlating rock layers by using rock types) Biostratigraphy (correlating rock layers by using fossils) Magnetostratigraphy (correlating rock layers by using magnetic reversals) Chemostratigraphy (correlating rock layers by using chemical or isotopic methods for correlating; e.g., oxygen isotopes or (iridium spike at end of Cretaceous) Chronostratigraphy (correlating rock layers by using absolute and/or relative time) Stratigraphic Methods

31. Geologic Time Scale Standard geologic time scale –Worldwide relative time scale –Subdivides geologic time based on fossil assemblages –Divided into eons, eras, periods, and epochs Precambrian - vast amount of time prior to the Paleozoic era; few fossils preserved Paleozoic era - “old life” –appearance of complex life; many fossils

32. Geologic Time Scale Mesozoic era - "middle life" –Dinosaurs abundant on land –Period ended by mass extinction Cenozoic era - "new life" –Mammals and birds abundant –We are currently in the Recent (Holocene) Epoch of the Quaternary Period of the Cenozoic Era –Most recent ice ages occurred during the Pleistocene Epoch of the Quaternary Period

33. Combining Relative and Numerical Ages Radiometric dating gives numerical time brackets for events with known relative ages –Individual layers may be dated directly –Radiometric dating of units above and below brackets age of units in between Geologic Time Scale –Divided into four Eons Hadean, Archean, Proterozoic, Phanerozoic –Precambrian (all time prior to Phanerozoic) represents 87% of geologic time)

34. Age of the Earth Numerical dating gives absolute age for Earth of about 4.56 billion years –Oldest age obtained for meteorites, believed to have been unchanged since the formation of the solar system –Earth and rest of solar system very likely formed at this time Geologic (deep) time is vast –A long human lifetime (100 years) represents only about 0.000002% of geologic time

35. Why Study of Historical Geology? Survival of the human species may depend on understanding how Earth’s subsystems work and interact and exploring the past is our only ‘laboratory’ for testing hypotheses. Knowing what occurred in the past can help us to understand our origins and place in both the Earth and the Universe.

36. Latest Precambrian / Early Paleozoic Supercontinent Rodinia, centered about the south pole, breaks apart. North America (Laurentia), Baltica, and Siberia moved North. Marine Invertebrates. North America: arc on the south. Baltica and Siberia moved in from the SE. Texas (505-570 Ma): Flat plain; remnants of eroded collisional belt (Llano). Shallow marine seas across much of Texas. Sandy sediment onshore, limestone offshore. Trilobites, brachiopods. http://vishnu.glg.nau.edu/rcb/globaltext.html

37. Precambrian Stromatolites

38. Cyanobacteria – green algae two kinds cyanobacteria from the Bitter Springs chert of central Australia, a site dating to the Late Proterozoic, about 850 million years old. On the left is a colonial chroococcalean form, and on the right is the filamentous Palaeolyngbya.Bitter Springs

39. Ediacaran Fauna Dickinsonia is known from Vendian rocks of south Australia and north Russia. It is often considered to be an annelid wormannelid worm

40. Ediacaran Fauna this unusual disc-shaped form with three-part (triradial) symmetry. Named Tribrachidium heraldicum, its affinities are still mysterious, although distant relationships have been proposed with either the Cnidaria (corals and anemones) or Echinodermata (urchins and seastars). Cnidaria Echinodermata Kimberella, one of the most fascinating Vendian fossils, has received a great deal of attention lately. It was hypothesized to be a box jellyfish (cubozoan)box jellyfish (cubozoan)

41. Ediacaran Fauna Nemiana is one of the simplest of all Vendian fossils, and is difficult to interpret. It seems to be an impression of a saclike body

42. ‘ The Small Shellies’

43. Burgess Shale Marrella splendensMarrella splendens is a small "arthropod" somewhat reminiscent of a trilobite TuzoiaTuzoia is a "bivalved" crustacean grossly similar to certain types of modern brine shrimp. specimen is only a small part of Anomalocaris, which was a large (up to 60cm or more) arthropod-like predator.

44. Burgess Shale Vauxia gracilentaVauxia gracilenta has a branching morphology: a sponge

45. Burgess Shale

46. Trilobites

48. Trace Fossils Worm trails Arthropod tracks Trilobite tracks

49. Latest Precambrian / Early Paleozoic Supercontinent Rodinia continues to break apart. Pieces move north. -Fish. -Glaciation. North America: Numerous plates and continental blocks move in from the south and east. The Taconic arc collides, forming the Taconic orogeny. Texas 438-505 Ma: Shallow marine seas across much of inland Texas. Warm-water limestone. Corals, brachiopods. http://vishnu.glg.nau.edu/rcb/globaltext.html

50. Middle / Late Paleozoic Remains of Rodinia (Gondwana) move northward to collide with Laurasia -- creating the super continent Pangaea and the Tethys Ocean. First land-plants. Baltica collides with North America in the Caledonian-Acadian orogeny. Texas 403-438 Ma: Shallow marine seas across much of west Texas - limestone. Corals, brachiopods. http://vishnu.glg.nau.edu/rcb/globaltext.html

51. Middle / Late Paleozoic Most drifting Rodinia blocks assembled into the super continent of Laurussia. Amphibians. Fish really get going. Ferns. Glaciation. North America: Caledonian-Acadian orogeny marks assemblage of Laurussia. Gondwana closed in from the south. An arc formed along western North America. Texas 360-408 Ma: shallow marine sandstones and limestones in west Texas. http://vishnu.glg.nau.edu/rcb/globaltext.html

52. Middle / Late Paleozoic Gondwana, with a large, developing glacier, nears southern Laurussia. Fern-forests. North America: The Antler arc collides with western North America creating the Antler orogeny. Texas 320-360 Ma: shallow marine seas inland. Shales and limestones. http://vishnu.glg.nau.edu/rcb/globaltext.html

53. Middle / Late Paleozoic Rodinia blocks of Laurussia and Siberia collide to form Laurasia. Reptiles. North America: Gondwana collides from the south. The resulting Appalachian, Ouachita, Marathon, Ural, Variscan, and Hercynian orogenies formed some of the largest mountains of all time. The Ancestral Rockies form. Texas 286-320 Ma: Ouachita Mountains. Collision formed inland basins filled by seas. Limestone, sandstone, shale.

54. Latest Paleozoic / Early Mesozoic The supercontinent Pangeae dominates the Permian Earth, lying across the equator. Extinctions! Trilobites go away. North America: A new arc approaches western North America. A new spreading center forms as Cimmeria rifts from Gondwana and opens the Tethyian Ocean. The western fringe of Pangaea lay along the eastern margin of the Pacific "ring of fire” subduction zone. Texas 245-286 Ma: Shallow marine inland of mountains. Reefs. Evaporites. Red shales. http://vishnu.glg.nau.edu/rcb/globaltext.html

55. Latest Paleozoic / Early Mesozoic Mammals. North America: Arc collision along western edge forms the Sonoman orogeny. As the Tethys Ocean expands, Cimmeria (Turkey, Iran, and Afghanistan) move northward towards Laurasia. Texas 208-245 Ma: shales and sandstones in NW. Start opening the GOM - red sandstone, shale, evaporites. http://vishnu.glg.nau.edu/rcb/globaltext.html

56. Middle Mesozoic Pangaea rotates; different components at different rates / in different directions -- rifts form. Birds. North America: Southern North Atlantic Ocean opens, continuing west into the Gulf of Mexico. The Cordilleran arc develops along Pacific margin. Arc forms on western side. Nevadan orogeny begins. Cimmeria begins collision with Laurasia - Cimmerian orogeny. Texas 144-208 Ma: Change in sediment direction. Shallow water deposition / evaporites in GOM. http://vishnu.glg.nau.edu/rcb/globaltext.html

57. Middle Mesozoic The Atlantic continues to expand as Pangaea breaks up. The Cimmerian orogeny continues. North America: Arcs and micro continents slam into western region. Laramide orogeny in Rockies. Texas 66-144 Ma: Influx of sediment from Rockies. Shallow Cretaceous sea way across Texas. Shallow liestones, shales. http://vishnu.glg.nau.edu/rcb/globaltext.html

58. Late Cretaceous / Present Rifts separate Africa and South America and then India, Australia, Antarctica. North America rifts from Europe. Old Gondwana lands(Africa, India, Australia) move north toward Eurasia, closing the Tethys Ocean and forming the Alpine-Himalayan mountains. The Atlantic lengthens / widens, the Sevier orogeny continues, and the Caribbean arc forms. Texas 65-144 Ma: continuing shallow limestone and shale deposition to the southeast (from Rockies). http://vishnu.glg.nau.edu/rcb/globaltext.html

60. Paleocene / Eocene Himalayan Orogeny. Alps and Pyrenees form. The modern patterns of Planet Earth appear. Atlantic continues to open. Rocky Mountains grow. Texas 65 - 35 Ma: shale and sandstone in southeast region prograde shoreline (from the Rockies). Volcanic activity in Panhandle. http://vishnu.glg.nau.edu/rcb/globaltext.html

61. Oligocene and Miocene Orogeny continues in the Mediterranean region and India nears its junction with southern Asia. Antarctica isolated. Southwestern North America intercepts the East Pacific Rise and a great extensional event, the Basin and Range orogeny begins. Texas 35-5 Ma: continued sandstone/shale deposition and progradation of shoreline (erosion of Rockies) http://vishnu.glg.nau.edu/rcb/globaltext.html

62. Present Note: Best data set available. http://vishnu.glg.nau.edu/rcb/globaltext.html

63. Fossils are the remains or traces of prehistoric organisms –Any evidence of past life Most common in sedimentary rocks –and in some accumulations of pyroclastic materials, especially ash They are extremely useful for determining relative ages of strata –geologists also use them to ascertain environments of deposition Fossils provide some of the evidence for organic evolution –many fossils are of organisms now extinct Fossils

64. Remains of organisms are called body fossils –mostly durable skeletal elements such as bones, teeth and shells How do Fossils Form? –rarely we might find entire animals preserved by freezing or mummification

65. Indications of organic activity including tracks, trails, burrows, and nests are called trace fossils A coprolite is a type of trace fossil consisting of fossilized feces that may provide information about the size and diet of the animal that produced it Trace Fossils

66. A land-dwelling beaver, Paleocastor, made this spiral burrow in Nebraska Trace Fossils

67. Fossilized feces (coprolite) of a carnivorous mammal –specimen measures about 5 cm long and contains small fragments of bones Trace Fossils

68. The most favorable conditions for preservation of body fossils occurs when the organism –possesses a durable skeleton of some kind –and lives in an area where burial is likely Body fossils may be preserved as –unaltered remains, meaning they retain their original composition and structure,by freezing, mummification, in amber, in tar –altered remains, with some change in composition or structure by being permineralized, recrystallized, replaced, carbonized Body Fossil Formation

69. Insects in amber Unaltered Remains Preservation in tar

70. Unaltered Remains 40,000-year- old frozen baby mammoth found in Siberia in 1971 –hair around the feet is still visible

71. Petrified tree stump in Florissant Fossil Beds National Monument, Colorado Altered Remains

72. Carbon film of a palm frond Altered Remains Carbon film of an insect

73. The fossil record is the record of ancient life preserved as fossils in rocks The fossil record is very incomplete because of: –bacterial decay –physical processes –scavenging –metamorphism In spite of this, fossils are quite common Fossil Record