What’s the oldest thing you have ever touched?

Evolution of Landforms and Organisms Continued – Part Two

Geology – Study of the Earth Geologic Terms Chemical Weathering Mechanical Weathering Age of Earth Absolute dating Trilobite Age of rocks Relative dating Ice core Fossils Radioactive dating Index Fossils Eons Law of superposition Geological Time Scale Eras –Periods -Epochs Unconformity

Trilobite The trilobites were the most successful species roaming the earth about 500 million years ago. 17,000 different species existed Trilobites were widely diverse and had an easily fossilized exoskeleton An extensive fossil record was left

Age of Earth? thousands - millions - billions trillions 4.6 Billion Years old

How is the Age of the Earth Determined? Absolute Age Relative Age

Relative Age or Absolute Age “No Ordinary Family”

Absolute 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 decayed Parent Isotope Stable Daughter Product Currently Accepted Half-Life Values Uranium-238 Lead-206 4.5 billion years Uranium-235 Lead-207 704 million years Thorium-232 Lead-208 14.0 billion years Rubidium-87 Strontium-87 48.8 billion years Potassium-40 Argon-40 1.25 billion years Samarium-147 Neodymium-143 106 billion years

Radioactive 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 1600 Therefore, in 1600 years, one gram of radium-226 will turn into half a gram of radium-226 and half a gram of something else After 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 elements Carbon-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 decay Radiometric 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

Every 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

Elements Used in Radioactive Dating Radioactive Element Half-Life (years) Dating Range (years) Carbon –14 5,770 500-50,000 Potassium – 40 1.3 billion 50,000-4.6 billion Rubidium –87 48.8 billion 10 mill – 4.6 bill Thorium – 232 14 billion Uranium – 235 713 million Uranium – 238 4.5 billion

Calculating 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 years How much carbon-14 will there be in 17,100 years? 0.125 g 0.8 g 0.1 g 0.025 g 5,700 is 3 times more than 17,100 Divide 5,700 / 17,100 = 3 1g X 0.5 = 0.5 0.5 X 0.5 = 0.25 0.25 x 0.5 = 0.125g

Determining 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.

Blocks Stack the blocks Do not stack according to size Which block is the oldest ? Which block is thy youngest?

Law of Superposition In 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. Kids Parents Grandparents Great-grandparents

Law 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 layers This should make sense The oldest sediments must be laid down before the younger ones can pile up on top.

Rock Layers

Blocks 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?

Blocks Continue tilting the blocks until the layers have reversed positions. Now…. Which block is the oldest ? Which block is thy youngest?

Unconformity An unconformity is a “missing” rock layer Plate movements can fold, tilt or turn rock layers An unconformity is a “missing” rock layer This sometimes makes it difficult to age rock layers An 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.

Unconformity 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.

Angular Unconformity The 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.

Angular Unconformity An 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.

Water Causes Mechanical and Chemical Weathering Iron oxidation water expands when it freezes

Chemical Weathering The main agent of chemical weathering is WATER Rocks react with water, gases and solutions (may be acidic); will add or remove elements from minerals.

Why 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”.

Mechanical Weathering Thermal expansion – heating and cooling of rocks heat causes expansion; cooling causes contraction. Freezeing –Thawing action of water in the cracks of rocks water expands when it freezes

Mechanical Weathering Animals can burrow beneath the ground and break up rocks and soil Plant roots can grow and crack and break up rocks and soil

The 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

Weathering Created the Grand Canyon

Ice Cores Studying ice cores helps in understanding how climate has changed - warmer and/or colder Ice forms layers similar to rock layers We 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

Ice Core

Paleontologists Paleontologists study fossils they find embedded in “sedimentary” rocks. They use the information to determine what the earth and life was like in the past. The fossil record explains about life in the past and how it and the environment has changed over time. The rest of ANSWER # 17 is on another slide - Put your pencil down

Fossils are our window to the past Fossils are our window to the past. They show us what life was like millions of years ago.

Fossils They are evidence of once-living things. They show how species have changed over time and how some species are related to one another. Fossils

Fossils can give us evidence of past life Fossils suggest that birds evolved from dinosaurs.

A fossil is a rock! Most fossils are formed of sedimentary rock. They are formed by compacting and cementing together layered sediments.

Most 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.

Fossils form Slowly It takes about 1 million years to form a sedimentary fossil.

Deposition + Time + Erosion = Fossils

ANSWERS for # 17 - Fossils Facts They give us evidence of past life Most fossils are found in sedimentary rocks Fossils form slowly Only the hard parts of an organism is preserved An 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 time They show us how organisms are related to one another.

Preserved Tracks Tracks 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.

Here’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.

Here’s the Proof!

Index Fossils Some 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 Urchin Ammonite

Ammonites are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geologic time periods

Trilobite The trilobites were the most successful species roaming the earth about 500million years ago. 17,000 different pecies existed Trilobites were widely diverse and had an easily fossilized exoskeleton An extensive fossil record was left

Geologic Time Scale

Geologic 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… Eon Era Period Epoch Largest amount of time in Earth’s history Pre-Cambrian Early Life Time when specific animals and plants evolved Lasted billions of years Paleozoic Age of Fishes Time when specific mountain ranges were formed Life evolves Mesozoic Age of Reptiles Example: Jurassic Period Cenozoic Age of Mammals

Organisms that existed during the Cenozoic Mesozoic Paleozoic Eras Age of Mammals Organisms that existed during the Cenozoic Mesozoic Paleozoic Eras Age of Reptiles Age of Fishes

Quiz

Answer: Absolute age of rocks Question 1 Radiometric dating was used in a lab. What was the scientist investigating? Relative age of rocks Absolute age of rocks How climate had changed over time What fossils the rock layer contained Answer: Absolute age of rocks

Question 2 Which of the following would not be a factor in the formation of a fossil? Earthquakes Hurricane Avalanche Forest Fire Answer: Earthquake Answer:

Question 3 Characteristics of an index fossil include. They came from animals with few hard parts They existed in very large numbers They were only found in a particular place on the earth They are very hard to identify Answer: They existed in very large numbers

Question 4 Answer: Sedimentary What type of rock are fossils most commonly found in? a. igneous b. metamophic c. sedimentary d. rocky or muddy Answer: Sedimentary

Answer: 4.6 Billion Years Old Question 5 According to rock records, the Earth is about how old? 4.6 million years old 4.5 billion years old 5.4 million years old 5.6 billion years old Answer: 4.6 Billion Years Old Answer: 4.6 billion years old

Question 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 fossils b. Proof of plate tectonics c. Evidence of volcanic eruptions d. An unconformity Answer: Unconformity

Answer: The Law of Superposition Questions 7 & 8 and 9 Could using the half-life of carbon-14 be used As a means of dating dinosaurs? Answer: NO Normally, the youngest layer of rock in a rock layer will be where? Answer: On the top What proof supports this evidence? Answer: The Law of Superposition Answer: Relative Age

Questions 10 plus Answer: Eon – Era- Period - Epoch What “calendar” shows the history of the Earth? Answer: Geologic Time Scale What is the main factor that makes each division different from one another? Answer: The organisms that existed What is the longest division of time? Answer: Eon What is the order of the divisions of time? Answer: Eon – Era- Period - Epoch

The End

Types of Fossils Not part of 8th grade EOG test There are 6 basic types of fossils Cast Mold Imprint Trace Petrification Whole Preservation Freezing Tar Pits Peat Bogs Mummification Amber

Cast The 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.

Mold A mold is the empty space fossil formed in the outward shape of the dead plant or animal. A mold is a shaped hole.

Imprint An imprint fossil forms when thin objects like leaves and minnows become trapped in fine mud and make impressions that harden into stone.

Trace A 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.

Petrification 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”.

Whole 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.

Unconformity