Presentation on theme: "Chapter 21 Fossils & the Rock Records"— Presentation transcript:
1 Chapter 21 Fossils & the Rock Records Produced by S. Koziol
2 21.1 The Geological Time Scale ObjectivesDescribe the geological time scaleDistinguish among the following geological time scale divisions: eons, era, period, and epochs
3 Geological time scaleThe geological time scale divides Earth’s history into units from its origin to the present.Remember scale issues….
4 Geologic timeGeologic time in order from shortest to longest epoch, period, era, eon
5 Geologic time – divisions? Periods are defined by the abundance or extinction of life-forms.
6 Geological time (continued) On the geologic time scale, the smallest unit of time is called an epoch.We are currently in the Holocene epoch of the Quaternary period.Greater collection of fossils has been found and paleontologists have more detailed knowledge of the events that occurred during those times.
7 Geological Time – most recent The most recent period is the QuaternaryThe Anthropocene is an informal geologic chronological term for the proposed epoch that began when human activities had a significant global impact on the Earth's ecosystems.
8 Geological Time - longer The Archean and Proterozoic are examples of eons.
9 Eras vs Periods Both are units of time on the geologic time scale. Eras are longer spans of time, measured in hundreds of millions to billions of years. They are defined by differences in life-forms found in rocks.Periods are usually measured in terms of tens of millions of years to hundreds of millions of years. They are defined by the life-forms that were abundant or became extinct during the time in which specific rocks were deposited.
11 21.2 Relative-age Dating of Rocks ObjectivesApply the principle for determining relative age to interpret rock sequences.Describe an unconformity and how it is formed within the rock record.
12 Laws of SuperpositionStudent guided , remember the foam boards
13 Undisturbed rock sequence The oldest rock layer in an undisturbed rock sequence occurs at the bottom of the sequence.Which book was laid down 1st?Which rock layer was laid down 1st?
14 The principle of superposition The principle of superposition states that, in an undisturbed sequence, the oldest rocks are at the bottom of the sequence and successive layers are younger than those below them.
15 Cross-cutting relationship You can use the principle of cross-cutting relationships to infer that a fault or an intrusion is younger than the rock it cuts across.
16 CorrelationThe matching of rock layers from one geographic area with those of another area is known as correlation.
17 UniformitarianismThe principle of uniformitarianism states that the processes occurring today have been occurring on Earth since it formed. However, the rate, intensity, and scale with which these processes occur have changed.
18 UnconformityWhen part of the rock record is destroyed, the erosional gap that forms is an unconformity.
19 Angular unconformityThe gap in the rock record that occurs between folded or uplifted rock layers and a sedimentary rock layer on top of them is called an angular unconformity.
20 NonconformityA buried erosional surface between a non-sedimentary rock and a sedimentary rock is called a nonconformity.A nonconformity in the Wind River gorge of Wyoming.
21 21.3 Absolute-age Dating of Rocks ObjectivesExplain the several different methods used by scientist to determine absolute age.Describe how objects are dated by the use of selected radioactive elements.Explain how annual tree rings and glacial varves are used to date geological events.
22 Dating techniques Relative-age dating Relative-age dating places the ages of rocks and the events that formed them in order, without exact dates. This is done by comparing one event with another or one rock with another rock.Absolute-age datingIn contrast, absolute-age dating determines the actual age of a rock, a fossil, or an object. This is done through radiometric dating, a process that determines the ratio of parent material to daughter product in a given sample of rock or fossil.
23 Half-lifeThe amount of time it takes for one-half of the original amount of an isotope to decay is known as its half-life.
24 Igneous Rocks and Minerals Radiometric datingRadiometric dating is used to determine the absolute age of a rock. This is done using the idea of half-life.ParentDaughtert1/2Useful RangeType of Material238U206Pb4.5 b.y>10 million years Igneous Rocks and Minerals235U207Pb710 m.y232Th208Pb14 b.y40K40Ar & 40Ca1.3 b.y>10,000 years87Rb87Sr47 b.y>10 million years14C14N5,730 y,000 yearsOrganic Material
25 Key BedA key bed contains distinctive material that geologists can easily recognize in the rock record and use as a time marker.
26 DendochronologyThe science of dendochronology uses the annual growth of tree rings to date events and environmental changes.
27 PermineralizationIn the process of permineralization, pore spaces within an organism’s shell are filled in with mineral substances.
28 21.4 Remains of organisms in the rock records ObjectivesDefine fossil.Explain several methods by which fossils can be preserved.Describe the characteristics of an index fossil.Discuss how fossils can be used to interpret Earth’s past physical and environmental history.
29 AmberFossil insects can be found imbedded in amber, the hardened sap of prehistoric trees.
30 MoldWhen the original parts of an organism in a sedimentary rock are weathered and eroded, a hollowed-out impression called a mold forms.
31 CastsNatural casts can be formed when minerals are deposited within the mold.
32 FossilsMolds, casts, coprolites, and petrified wood are all example of fossils
33 Original Preservation (rare) Mummified animals found in dry caves can be examples of fossils with original preservation.Discovered in 1977, this six-to-eight-month-old woolly mammoth baby named Dima is pictured in situ near Kirgiljach River in northeast Siberia.5,300 year old Iceman discovered in Austrian Alps, 1991
34 FossilsFossils are the remains or evidence of once-living plants or animals. They provide clues about Earth’s past environmental conditions and evolutionary changes in organisms over time. They also help to correlate rock layers from one area to another.
35 Index fossilsGeologists use index fossils to correlate rock layers over large geographic areas or to date a particular rock layer. To be useful, an index fossil must be easily recognized, abundant, and widely distributed geographically. It must also have lived over a short period of time.
36 Index fossils (continued) Index fossils are useful to geologists if the fossils have lived over a short period of time
37 EvolutionThe adaptation of life-forms to changes in the environment is known as evolution.
38 Evolution (continued) Evolution is the process by which organisms adapt to changes in their environments.
39 End of the PrecambrianThe end of the Precambrian is marked by the appearance of organisms with hard parts.Remember this is speaking to the end of the pre-Cambrian