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Earth History. Objectives: Define Relative Age Define Absolute Age Explain the principles of relative time including uniformitarianism, superposition, and original horizontality
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Earth History Objectives: Define Relative Age Define Absolute Age Explain the principles of relative time including uniformitarianism, superposition, and original horizontality Explain how geologic events can be used to determine relative time including inclusions, cross-cutting relationship, contact metamorphism, and unconformities Describe radioactive decay Calculate half-life of a radioactive isotope Identify various types of fossils Explain the various theories of how life began on Earth Explain extinction Define Index fossils Explain the differences in each of the major geologic eras Know how to use Geologic History of New York State chart ESRT page 8 and 9
Fossils and the Past • A. A fossil is the remains or the evidence of a living thing. B. Formation of Fossils: 1. Most fossils are incomplete because usually only the hard parts of a plant or animal become fossils. 2. The soft flesh of dead organisms was usually eaten by animals or decayed before it could form into a fossil. 3. Circle the organisms below that would most likely become a fossil.
2. a. Most fossils form when organisms are buried in sediments. b. Sediments often harden and change into rock. When this happens, organisms may be trapped in the rock. Most fossils are found in ________________ rocks. Sedimentary Living Organism Burial of hard parts by sediments Sediment becomes rock Uplifting- Weathering & erosion expose fossil
c. Fossils are almost never found in ___________ rocks because magma is found deep within Earth where no living things exist, and lava at the surface burns organisms before fossils can form. Igneous Metamorphic d. Fossils are rarely found in _______________ rocks because heat, pressure, and/or chemical activity that causes a rock to change, also destroys or damages the fossils.
C. Types of Fossils 1. ___________________ and __________________ Casts Molds Cast a. ________________ an empty space in the shape of the organism. This occurs when the hard parts of an organism decay and/or the hard parts are dissolved by chemicals. Mold b. _______________ occurs when minerals fill a mold and harden into the shape of the original organism.
Imprints (Impressions) 2. ___________________- occurs when leaves and feathers leave an impression in soft sediment (mud) that later hardens into rock. Amber 3. __________________ - occurs when insects are trapped and become embedded in resin (tree sap) that hardens.
Ice 4. __________________ - occurs when an organism is preserved in ice. Tar 5. __________________ - occurs when animals are trapped in tar pits as in the LaBrea Tar Pits of California.
Iceman "In order for a body to be completely mummified as in this case, the body must first dry completely then covered in ice and snow." The mummy was an male adult remarkably well preserved. The condition of his equipment and organic material were also preserved in good condition. The age of the body is about 3,300 BC or late Stone Age. http://www.mc.maricopa.edu/dept/d10/asb/anthro2003/legacy/iceman/iceman.html
Petrified 6. __________________ - occurs minerals dissolved in ground water gradually replace the original tissues of plants and animals. 7. __________________ - occurs the carbon in the tissues of organisms leave a residue/thin film of carbon on sediment which then hardens into rock. Carbonaceous film
D. Interpreting Fossils 1. Fossils indicate that many different kinds of life forms existed at different times in Earth’s history. 2. When fossils are arranged according to age, they show that Certain living things have changed or evolved over time.
3. Fossils indicate how For example, fossils of marine organisms can be found in rocks that are presently high above sea level. the Earth’s surface has changed.
Earth’s past climate. 4. Fossils give clues to Since coral today live in the warm waters of equatorial regions, between 30° N and 30° S latitude, we can infer that N.Y.S. had a warmer climate in the past.
5. Fossils tell about the appearance and activities of past life. For example, fossil teeth give clues about the kind of food the animal ate.
II. Relative Dating A. Relative Age- the age of something compared to something else. B. The Geologic Column- an ideal sequence of rock layers created by combining data from all known rock sequences at various locations. Correlation
C. Principle of Superposition- In an undisturbed set of sedimentary rock layers, the oldest rock is at the bottom and the youngest is on the top. YOUNGEST OLDEST
D. Disturbed Rock Layers and Relative Dating “Principle of Cross-Cutting Relationships” A fault is ______________ than the rock layers it cuts across. YOUNGER An igneous intrusion is ______________ than the rock layers it penetrates YOUNGER = Contact metamorphism
Folding Layers of sediment are deposited in flat-lying layers “ Principle of Original Horizontality” Tilting The folding and tilting of rock layers are events that are ___________ than the rock layers they effect. YOUNGER
Regents Question 3 The photograph represents a mountainous area in the Pacific Northwest. Scientists believe that sedimentary rocks like these represent evidence of crustal change because these rocks were 1. formed by igneous intrusion 2. faulted during deposition 3. originally deposited in horizontal layers 4. changed from metamorphic rocks
E. Unconformity- A buried erosional surface separating two rock layers of different ages that show that sediment deposition was not continuous. Deposition- formation of horizontal rock layers Uplifting/ folding Erosion of surface layers Unconformity Subsidence- sinking down of earth’s layers followed by deposition of new sedimentary layers
Regents Questions The unconformities shown in the cross section represent 1. buried erosional surfaces 2. locations of index fossils 3. volcanic ash deposits 4. boundaries between oceanic and continental crust • The unconformities shown in the cross section represent • Letter X • Letter E • Letter Q • Letter Y
F. Index Fossils- a fossil that is used to date the rock layers in which it is found. 1. An organism that lived during a relatively short, well-defined time span. 2. Organism lived in a wide geographic area.
Practice G. Determining Relative Age: Identify both the oldest rock or event and the youngest rock or event: 4 3 2 1 Siltstone Shale 6 5 4 3 Conglomerate 2 Fault 1
3. Shale Sandstone 4. Shale Siltstone 5. Sandstone Shale
6. Limestone Igneous Intrusion 7. Sandstone Igneous Intrusion
Shale Fault Siltstone Igneous Intrusion
III. Radioactive Dating- determining the absolute age of a rock or fossil A. Absolute Age- the measure of how many years old an event occurred or an organism lived. B. Radioactivity- the ability of an element to change spontaneously into a different element by losing or gaining matter from the nucleus of an atom. E.S.R.T page ____ 1
C. Radioactive Decay 1. __________ or _______ element = an atom that has an unstable nucleus that changes spontaneously, or “decays”. Radioactive parent Decay daughter 2. __________ or __________element = the stable element that is the result of the spontaneous change in a radioactive element.
3. Half-life = the TIME it takes for ONE-HALF of a radioactive element to change into a decay element. Or PARENT Daughter element 4. The rate of decay (the half-life period of time) is NOT affected by any outside condition such as: a. b. c. Heat Pressure Chemical action
Half-lives of radioactive elements are unique for each element Carbon-14 5. ______________ has a short half-life and is therefore used to date the remains of __________________ such as _______________________________________________________. Living things Bones, Wood, Leather
100% 50% 25% 12.5% 6.25% 1:3 1:7 1:16 1:1
Practice: Making a Time-Table (T-table) After an organism dies, how much percent of Carbon-14 is remaining after 5 half-lives? Time Mass 0 100% 1 50% 25% 2 3 12.5% 4 6.25% 5 3.125%
Practice: Making a Time-Table (T-table) If a dinosaur contained 200 grams of Carbon-14, how much will be remaining after 34,200 years? Time (yrs) Mass (grams) 0 200 5700 100 50 11,400 17,100 25 22,800 12.5 28,500 6.25 34,200 3.125
A rock sample contains 8 grams of Potassium-40 when it was formed but now contains only 2 grams due to radioactive decay. What is the approximate age of this rock? Time (yrs) Mass (grams) 0 8
IV. Geologic Time A. The Geologic Time Scale divides Earth’s history into sections of time. B. The units or sections of geologic time include: 1. 2. 3. 4. Eon longest Era Period Epoch shortest
C. The boundaries between geologic time intervals represent major changes on Earth which include: 1. 2. 3. Emergence of different life Peak Developments of species Major Extinctions D. Geologic Time began when Earth first formed about ______________________ years ago. 4600 million
Today Mesozoic Formation of Earth Precambrian Cenozoic Paleozoic 0 65 = 1.4% 4500 0.35 cm Cenozoic 65 65 186= 4% 4500 186 1 cm Mesozoic 251 293= 6.5% 4500 293 1.625 cm Paleozoic 544 3956= 88% 4500 22 cm 3956 Precambrian 4,500
reptiles Corals reptiles forests amphibians Armored fish insects Eurypterids Land plants Invertebrates fish Trilobites Marine animals with shells Life Soft-bodied
humans mammals ~50% of life dinosaurs Flowering plants birds dinosaurs dinosaurs mammals ~90% of life
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