2Evolution of Landforms and Organisms Continued – Part Two
3Geology – Study of the Earth Geologic Terms Chemical WeatheringMechanical WeatheringAge of EarthAbsolute datingTrilobiteAge of rocksRelative datingIce coreFossilsRadioactive datingIndex FossilsEonsLaw of superpositionGeological Time ScaleEras –Periods -EpochsUnconformity
4TrilobiteThe trilobites were the most successful species roaming the earth about 500 million years ago.17,000 different species existedTrilobites were widely diverse and had an easily fossilized exoskeletonAn extensive fossil record was left
5Age of Earth? thousands - millions - billions trillions 4.6 Billion Years old
6How is the Age of the Earth Determined? Absolute AgeRelative Age
7Relative Age or Absolute Age “No Ordinary Family”
8Absolute Age and Rocks Absolute age tells the actual age of a rock. Radioactive Decay or Radiometric Dating is one method that gives the age of a rock by comparing the amount of radioactive material in the rock with the amount that has decayedParent IsotopeStable Daughter ProductCurrently Accepted Half-Life ValuesUranium-238Lead-2064.5 billion yearsUranium-235Lead-207704 million yearsThorium-232Lead-20814.0 billion yearsRubidium-87Strontium-8748.8 billion yearsPotassium-40Argon-401.25 billion yearsSamarium-147Neodymium-143106 billion years
9Radioactive Dating - Carbon Dating The half-life of a radioactive element is the time it takes for half of its atoms to decay into something else.For example, the half-life of radium-226 is 1600Therefore, in 1600 years, one gram of radium-226 will turn into half a gram of radium-226 and half a gram of something elseAfter another 1600 years have elapsed, only a quarter of a gram of the original radium-226 will remain.Finding the ratio of parent to daughter elementsCarbon-14 is an isotope that has a half life of 5,700 year old.Half-life – The time it takes for half of the atoms in an isotope to decayRadiometric Decay – Process that uses properties of atoms in rocks and other objects to determine their ages.Radioactive Dating – calculating the absolute age of a rock by measuring the amounts of parent and daughter materials in a rock and by knowing the half-life of the parent material
10Every living thing contains Carbon -14 It has been used to date fossils such as frozen mammoths, pre-historic humans, plants and animals that lived up to about 50,000 years ago.It’s half-life is only 5,700 years so it can’t be used to date ancient fossils or rocks.Carbon dating tells when this mammoth died
11Elements Used in Radioactive Dating Radioactive ElementHalf-Life (years)Dating Range (years)Carbon –145,770500-50,000Potassium – 401.3 billion50, billionRubidium –8748.8 billion10 mill – 4.6 billThorium – 23214 billionUranium – 235713 millionUranium – 2384.5 billion
12Calculating Half Life Carbon-14 decreases by half every 5,700 years. A sample of 1g of carbon-14 will decrease by half to 0.5 after 5,700 yearsHow much carbon-14 will there be in 17,100 years?0.125 g0.8 g0.1 g0.025 g5,700 is 3 times more than 17,100Divide 5,700 / 17,100 = 31g X 0.5 = 0.50.5 X 0.5 = 0.250.25 x 0.5 = 0.125g
13Determining the Absolute Age of Rock Layers Radioactive Dating A technique for measuring the age of an object or sample of material by determining the ratio of the concentration of a radioisotope to that of a stable isotope in it; for example, the ratio of carbon-14 to carbon-12 reveals the approximate age of bones, pieces of wood, and other archeological specimens.
14Blocks Stack the blocks Do not stack according to size Which block is the oldest ?Which block is thy youngest?
15Law of SuperpositionIn undisturbed sedimentary ROCK, the oldest layers are deeper down, at the bottom and the youngest layers are closer to the top.Kids are younger & come after parents & grandparents.KidsParentsGrandparentsGreat-grandparents
16Law of Superposition – Rock Layers This law states that if a rock layer has not been disturbed then;Older layers of rock lie beneath younger rock layersThis should make senseThe oldest sediments must be laid down before the younger ones can pile up on top.
18Blocks Tilt the blocks to at an angle. What happens to the rock layers when they are tilted?Which block is the oldest ?Which block is thy youngest?
19BlocksContinue tilting the blocks until the layers have reversed positions.Now….Which block is the oldest ?Which block is thy youngest?
20Unconformity An unconformity is a “missing” rock layer Plate movements can fold, tilt or turn rock layersAn unconformity is a “missing” rock layerThis sometimes makes it difficult to age rock layersAn unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record.
21Unconformity Igneous or metamorphic rock is a nonconformity Unconformity Igneous or metamorphic rock is a nonconformity. The boundary represents a nonconformity. Igneous or metamorphic rock may be uplifted to Earth’s surface by crustal movements. Once the rock is exposed, it erodes. Sediments are deposited on the eroded surface.
22Angular UnconformityThe most obvious kind is the angular unconformity.Rocks below the unconformity are tilted and sheared off, and rocks above it are level. The angular unconformity tells a clear story:First a set of rocks was laid down.Then these rocks were tilted, then eroded down to a level surface.Then a younger set of rocks was laid down on top.
23Angular UnconformityAn angular unconformity forms when rock deposited in horizontal layers is folded or tilted and then eroded. When erosion stops, a new horizontal layer is deposited on top of a tilted layer. When the bedding planes of the older rock layers are not parallel to those of the younger rock layers deposited above them, an angular unconformity results.
24Water Causes Mechanical and Chemical Weathering Iron oxidationwater expands when it freezes
25Chemical Weathering The main agent of chemical weathering is WATER Rocks react with water, gases and solutions(may be acidic); will add or remove elementsfrom minerals.
26Why is the Statue of Liberty Green? The statue is made of copper. Copper is naturally the color of a shiny penny. But, when copper is exposed to rain it tarnishes. This is chemical weathering. The rain contains copper carbonate, maybe sulfuric acid which gives it the green color. It turns the statue into copper oxide and other elements due to “oxidation”.
27Mechanical Weathering Thermal expansion – heating and cooling of rocksheat causes expansion; cooling causes contraction.Freezeing –Thawing action of water in the cracks of rockswater expands when it freezes
28Mechanical Weathering Animals can burrow beneath the ground and break up rocks and soilPlant roots can grow and crack and break up rocks and soil
29The salts in our oceans is a result of weathering of rocks and soil. One way minerals and salts are deposited into the oceans is from outflow from rivers, which drain the landscape, thus causing the oceans to be salty.Rain contains some dissolved carbon dioxide from the surrounding air. This causes it to be slightly acidic. The rain physically erodes the rock and the acids chemically break down the rocks and carries salts and minerals into the oceans
31Ice Cores Studying ice cores helps in understanding how climate has changed - warmer and/or colderIce forms layers similar to rock layersWe have also learned about the Ice Ages by discovering fossils that are missing in rock layers.The layers record amounts of gases and elements present in the atmosphere and water at a particular time in history
33Paleontologists Paleontologists study fossils they find embedded in “sedimentary”rocks.They use the informationto determine what the earth andlife was like in the past.The fossil record explains aboutlife in the past and how it andthe environment has changedover time.The rest of ANSWER # 17 is onanother slide - Put your pencil down
34Fossils are our window to the past Fossils are our window to the past. They show us what life was like millions of years ago.
35Fossils They are evidence of once-living things. They show how species have changedover time and how some species arerelated to one another.Fossils
36Fossils can give us evidence of past life Fossils suggest that birds evolved from dinosaurs.
37A fossil is a rock! Most fossils are formed of sedimentary rock. They are formed by compacting and cementing together layered sediments.
38Most Fossils form in What Kind of Rock ? Layer upon layer of sand, mud, dead plants and animals and other small pieces build up and their weight compacts and cements the layers together.
39Fossils form SlowlyIt takes about 1 million years to form a sedimentary fossil.
41ANSWERS for # 17 - Fossils Facts They give us evidence of past lifeMost fossils are found in sedimentary rocksFossils form slowlyOnly the hard parts of an organism is preservedAn organism has to be buried quickly in order to become fossilized.They give us clues about the size, shape, growth patterns and structures of extinct organisms.They show us how organisms have changed over timeThey show us how organisms are related to one another.
42Preserved TracksTracks give us evidence of the size, weight and stride of the animal. If several tracks are found that can be evidence of lifestyle: social grouping an interactions among species.
43Here’s the Story!Sometime between 200 and 205 million years ago a meat eating Eubrontes dinosaur crouched on the shore of lake Dixie. Perhaps it had been eating fish in the nearby deep water. The dinosaur may have been a Dilophosaurus weighing around 1,000 pounds, measuring 6 feet high at the hip and 18 feet long. He sat down leaving the imprint of his feet, heel, pelvis, hands, and tail in the sand. In the process of getting up he shuffled his feet, leaving a second set of impressions. He arose and walked away. For some reason his impressions were buried waiting to be discovered at a later date.
45Index FossilsSome species inhabited Earth for long periods of time without changing.INDEX FOSSILS existed for short periods of time, were abundant and were found in lots of different places on Earth.Index Fossils have been found in many places throughout the Earth and geologists use them to date the age of rock layers.Sea UrchinAmmonite
46Ammonites are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geologic time periods
47TrilobiteThe trilobites were the most successful species roaming the earth about 500million years ago.17,000 different pecies existedTrilobites were widely diverse and had an easily fossilized exoskeletonAn extensive fossil record was left
49Geologic Time Scale A timeline that organizes the events in Earth’s history. The divisions are based on organisms that existed during that time period and the geologic events that occurred: mountains forming, seas rising, plains forming, etc…EonEraPeriodEpochLargest amount of time in Earth’s historyPre-CambrianEarly LifeTime when specific animals and plants evolvedLasted billions of yearsPaleozoicAge of FishesTime when specific mountain ranges were formedLife evolvesMesozoicAge of ReptilesExample: Jurassic PeriodCenozoicAge of Mammals
53Answer: Absolute age of rocks Question 1Radiometric dating was used in a lab. What was the scientist investigating?Relative age of rocksAbsolute age of rocksHow climate had changed over timeWhat fossils the rock layer containedAnswer: Absolute age of rocks
54Question 2Which of the following would not be a factor in the formation of a fossil?EarthquakesHurricaneAvalancheForest FireAnswer: EarthquakeAnswer:
55Question 3 Characteristics of an index fossil include. They came from animals with few hard partsThey existed in very large numbersThey were only found in a particular place on the earthThey are very hard to identifyAnswer: They existed in very large numbers
56Question 4 Answer: Sedimentary What type of rock are fossils most commonly found in?a. igneousb. metamophicc. sedimentaryd. rocky or muddyAnswer: Sedimentary
57Answer: 4.6 Billion Years Old Question 5According to rock records, the Earth is about how old?4.6 million years old4.5 billion years old5.4 million years old5.6 billion years oldAnswer: 4.6 Billion Years OldAnswer: 4.6 billion years old
58Question 6 Answer: Unconformity A paleontologists discovers a gap of about 2 million years in the rock layer he is investigating and records this as being…a. An extinction of several fossilsb. Proof of plate tectonicsc. Evidence of volcanic eruptionsd. An unconformityAnswer: Unconformity
59Answer: The Law of Superposition Questions 7 & 8 and 9Could using the half-life of carbon-14 be usedAs a means of dating dinosaurs?Answer: NONormally, the youngest layer of rock in a rocklayer will be where?Answer: On the topWhat proof supports this evidence?Answer: The Law of SuperpositionAnswer: Relative Age
60Questions 10 plus Answer: Eon – Era- Period - Epoch What “calendar” shows the history of the Earth?Answer: Geologic Time ScaleWhat is the main factor that makes each divisiondifferent from one another?Answer: The organisms that existedWhat is the longest division of time?Answer: EonWhat is the order of the divisions of time?Answer: Eon – Era- Period - Epoch
63Types of Fossils Not part of 8th grade EOG test There are 6 basic types of fossilsCastMoldImprintTracePetrificationWhole PreservationFreezing Tar PitsPeat Bogs MummificationAmber
64CastThe fossil formed by filling the shaped space left in rock by a dissolved plant or animal.You can think of this as the shape of the jello when it comes out of the mold.
65MoldA mold is the empty space fossil formed in the outward shape of the dead plant or animal.A mold is a shaped hole.
66ImprintAn imprint fossil forms when thin objects like leaves and minnows become trapped in fine mud and make impressions that harden into stone.
67TraceA trace fossil results from animal or plant activity, such as tracks, trails, burrows or roots.These fill with mud that takes their shape and then it hardens into stone.
68Petrification A petrification fossil is the most detailed type. It is the process by which living things are copy-replaced by dissolved minerals. Detail down to the cell level can be seen.They have “inside detail”.
69Whole Preservation Whole preservation is the rarest fossil. The entire body of a plant or animal, including the soft parts, is preserved.Frozen mammoths, mummies, bog people, tar pit tigers and amber are examples.