Copy-of-W6-Geologic-Time-Scale.pptx

Geologic Time Scale  you are expected to: 1. Explain how relative and absolute dating were used to determine the subdivisions of geologic time (S11/12 ES-le-27) and 2. Describe how the Earth’s history can be interpreted from  1.How is the age of the Earth determined? It is determined through...

Geologic Time Scale  you are expected to: 1. Explain how relative and absolute dating were used to determine the subdivisions of geologic time (S11/12 ES-le-27) and 2. Describe how the Earth’s history can be interpreted from  1.How is the age of the Earth determined? It is determined through ________. A. clock C. relative dating B. fossil D. absolute dating 2.What is the correct order of categories for the geologic time scale from longest to shortest? A. eon, era, period, epoch B. era, epoch, eon, period C. era, eon, period, epoch D. eon, epoch, period, era  3.How many periods are there in the Cenozoic Era? A. 1 B. 2 C. 3 D. 4 4.How old is the Earth as believed by Paleontologists? A. 2015 years old C. 3.6 billion years old B. 4.6 million years old D. 4.6 billion years old 5. Which division on the geologic time scale is the shortest? A. eon C. era B. epoch D. period  Geologic Time Scale Objective: Identify the different eras, periods and epochs in the Geologic Time Scale (GTS). Procedure: 1. Study the geologic time scale diagram below. 2. Identify the era, period or epoch labeled by the letters A, B, C, D and E. 3. Pick the correct answer from the word bank below to complete the diagram. 4. Write your answer on a separate sheet.  Geologic Time The first principle you need to understand about geologic time is that the laws of nature are always the same. This means that the laws describing how things work are the same today as they were billions of years ago. For example, water freezes at 0°C. This law has always been true and always will be true. Knowing the natural laws helps you think about the Earth's past because it gives you clues about how things happened very long ago. It means that we can use present day processes to interpret the past. Imagine you find fossils of sea animals in a rock. The laws of nature say that the sea animals must have lived in the sea. That law has never changed, so the rock must have formed near the sea. The rock may be millions of years old, but the fossils in it are a clue for us today about how it formed.  Now imagine that you find that same rock with fossils of a sea animal in a place that is very dry and nowhere near the sea. How could that be? Remember that the laws of nature never change. Therefore, the presence of the fossil means that the rock formed by the sea. This tells you that even though the area is now dry, it must have once been underwater. Clues like this have helped scientists learn that the Earth's surface features have changed many times. Spots that were once covered by warm seas may now be cool and dry. Places that now have tall mountains may have once been low, flat grounds. These kinds of changes take place over many millions of years, but they are still slowly going on today. The place where you live right now may look very different in the far future.  How relative and absolute dating were used to determine the subdivisions of geologic time? The clues in rocks help scientists put together a picture of how places on Earth have changed. Scientists noticed in the 1700s and 1800s that similar layers of sedimentary rocks all over the world contain similar fossils. They used relative dating to order the rock layers from oldest to youngest. In the process of relative dating, scientists do not determine the exact age of a fossil but do learn which ones are older or younger than others. They saw that the fossils in older rocks are different from the fossils in younger rocks. For example, older rock layers contain only reptile fossils, but younger rock layers may also contain mammal fossils.  Scientists divided Earth's history into several chunks of time when the fossils showed similar things living on the Earth. They gave each chunk of time a name to help them keep track of how Earth has changed. For example, one chunk of time when many dinosaurs lived is called the Jurassic era. We find fossils of Earth's first green plants from the chunk of time named the Ordovician era. Many of the scientists who first assigned names to times in Earth's history were from Europe. As a result, many of the names they used came from towns or other local places where they studied in Europe.  Ordering rock layers from oldest to youngest was a first step in creating the geologic time scale. It showed the order in which life on Earth changed. It also showed us how certain areas changed over time in regard to climate or type of environment. However, the early geologic time scale only showed the order of events. It did not show the actual years that events happened. With the discovery of radioactivity in the late 1800s, scientists were able to measure the exact age in years of different rocks. Measuring the amounts of radioactive elements in rocks let scientists use absolute dating to give ages to each chunk of time on the geologic time scale.  How do marker fossils relate to geologic time? Another cool thing they have found in rocks tell us more about the story of the historical past of the Earth, the fossils. Scientists define fossils as any trace of living creatures such as recognizable structure or impression of a structure of an organism like skeleton, trails or fecal remains that are embedded in very old rocks which are at least 5000 years old.  There are certain fossils of animals or plants that are preserved in the rock record of the Earth that identify a particular span of geologic time. They are called marker fossils or guide fossils. Marker fossils are the basis for defining boundaries in the geologic time scale and also for the correlation of strata.  What is Geologic Time? Geologic time is the chronology of the Earth’s formation, changes, development, and existence. These events are measured on a geological time scale. Scientists do not measure geologic time on a clock or calendar. They use a linear timeline based on the age of rocks and their corresponding fossils as well as the change in life that occurred over millions of years.  The geologic time scale is a system of chronological measurement that relates stratigraphy to time. It is used by geologists and paleontologists to describe the timing and relationships between events that have occurred throughout Earth’s history.  Geologists have divided Earth’s history into a series of time intervals. These time intervals are not equal in length like the hours in a day. Instead, the time intervals vary in length. This is because geologic time is divided using significant events in the history of the Earth  What is the Boundary “Events”? The boundary between the Permian and Triassic is marked by a mass extinction in which a large percentage of Earth’s plant and animal species were eliminated. Another is the boundary between the Precambrian and the Paleozoic which is marked by the first appearance of animals with hard parts.  Geologic Time Scale (GTS) The geologic time scale is the “calendar” for events in Earth history. It subdivides all time into named units of abstract time arrange in descending order of duration namely eons, eras, periods, epochs, and ages. The enumeration of those geologic time units is based on stratigraphy, which is the correlation and classification of rock strata. The fossil forms that occur in the rocks provide the chief means of establishing a geologic time scale, with the timing of the emergence and disappearance of widespread species from the fossil record being used to delineate the beginnings and endings of ages, epochs, periods, and other intervals.  Era The smaller time interval that divides an EON. The Phanerozoic is divided into three eras: Cenozoic, Mesozoic and Paleozoic. Very significant events in the earth’s history are used to determine the boundaries of the era.  Most of our knowledge of the fossil record comes from the three eras of the Phanerozoic eon. The Paleozoic ("old life") era is characterized by trilobites, the first four-limbed vertebrates and the ancestors of land plants. The Mesozoic ("middle life") era represents the "age of dinosaurs," though also is noteworthy for the first appearances of mammals and flowering plants. Finally, the Cenozoic ("new life") era is sometimes called the "age of mammals" and is the era during which we live today.  Periods Just as eons are subdivided into eras, eras are subdivided into units of time called periods. The most well- known of all geological periods is the Jurassic period of the Mesozoic era (the movie Jurassic Park, of course, has something to do with that).  The Paleozoic era is divided into six periods. From oldest to youngest, these are the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Note that in the United States, the Carboniferous is divided into two separate periods: the Mississippian and the Pennsylvanian  Epochs and Ages Periods of geological time are subdivided into epochs. In turn, epochs are divided into even narrower units of time called ages. For the sake of simplicity, only the epochs of the Paleogene, Neogene, and Quaternary periods are shown on the time scale at the beginning of the discussion. It is important to note, however, that all of the periods of the Phanerozoic era are subdivided into the epochs and ages.  The Paleogene period is divided into--from oldest to youngest--the Paleocene, Eocene, and Oligocene epochs. The Neogene is divided into the Miocene and Pliocene epochs. Finally, the Quaternary is divided into the Pleistocene and Holocene epochs. Some geologists now think that--since humans are having such a notable impact on the Earth and its life--a new, youngest epoch should be added to the Quaternary: the Anthropocene. There is still considerable discussion in the geological community about whether this epoch should be added, as well as debate about what characteristics should define its beginning.  The Earth’s Story Pre-Cambrian Era The Earth’s surface passed through a molten stage solidifying into rocks. As it cooled the water vapor in the surrounding gaseous matter condensed and fell as rain, forming rivers and oceans on the solid surface. A series of mountain building, faulting and volcanic eruptions interrupted by erosion took place. Simple seaweeds and bacteria were the only forms of life known to have lived in this era.  Building of mountains and eroding of Earth’s crust, jellyfish and sponges had begun to develop. Few are known of this era. Some continents were formed during this period. The carbon content of sedimentary rocks indicates an abundance of life. But these life forms did not have skeletons and other hard parts. The hot climate was broken up by cold period and formed glaciers that covered large portions of the continents.  Paleozoic Era Six divisions of Paleozoic Era: Cambrian period Shallow inland seas covered large portions of the continents. The oceans rose as the climate became warmer and the glaciers melted. During this period, the continents rose because of great mountain building, volcanism, followed by erosion. Life remained in the seas. Starfish and trilobites became abundant. Over 1000 species have been identified from fossils. They have all disappeared now from the earth.  a) Ordovician period Narrow seas began in the continents. About a half of the continents were covered by the seas. Marine fossils formed in these continental seas. The continents again rose before the end of this period. The first animals with backbones appeared in the water environment. Ostracoderms (bony armored animals) became abundant. No life had yet appeared on land. The climate remained warm.  b) Silurian period Another period of sea spreading in the continents began. Volcanic eruptions on the sea floor and mountain building eventually caused the seas to fall back. The climate remained warm. Animals with backbones develop further in the seas. Sea scorpions about 3m long appeared. Corals became abundant. Sea plants developed more complex parts. Leafless plants appeared on land for the first time.  c) Devonian period It was a period of extensive mountain building and volcanic activity, followed by extensive erosion. The climate was warm, even semi-dry in places with heavy seasonal rains. The first fish evolved. Primitive sharks about 20m long appeared. This is the “Age of Fish” Some animals started to adapt themselves to living partially on land and partially in water. In the later part of the period, millipedes, mites, spiders, and wingless insects appeared on land. Plants developed roots, stems, and leaves. They varied from tiny centimeter- sized species to 15m high tress.  d) Carboniferous period Shallow seas spread in the continents. In other areas large swamps covered with giant trees over 35 m high developed. At the close of the period the giant trees died. Their decay and burial eventually formed the great coal beds that are now being mined. The climate was warm and moist. On land, giant reptiles such as the dinosaurs and giant insects began to develop. They lived mostly at the edges of the swamps.  e) Permian period Continental seas were cut off from the oceans and turned into wide lakes by folding of the Earth’s crust. Very high mountains formed in most continents.  Mesozoic Era a) Triassic period The continents were covered with vast deserts and high mountains. Widespread erosion formed great beds of sandstone in the shallow seas in and around the continents. The climate was hot and dry, becoming more humid and having more rains in the latter part of the period. The dry period prevented the growth of most plants on land. During this period an increase in rainfall encouraged the growth of ferns and pine trees on land. Reptiles continued to dominate the animal group. Fish-like reptiles developed.  b) Jurassic period The seas spread in the continents again. The high mountains eroded in the Triassic period were reduced to low hills. The climate was mild with enough rainfall to cause ferns and pine trees to increase in number. The fish-like reptiles in the seas became abundant. A bird-like reptile developed.  c) Cretaceous period Rivers flowed slowly on the eroded land to form huge deltas. The climate remained mild as in the Jurassic period. Flower-bearing plants evolved. Giant bird-like reptiles increased in number. Dinosaurs, the ruling group of reptiles, still dominated the land. By the end of the period, they died out. Mammals began to appear.  Cenozoic Era A) Tertiary period 1.Paleocene epoch Violent earthquakes, volcanic eruptions and mountain buildings began the formation of the Alps in Europe, the Himalayas in Asia, the Rockies in North America and the Andes in South America characterized the period. Flowering plants became dominant on land. Mammals increased in number and in variety.  2. Eocene epoch The Alps, Himalays and Andes continued to grow. The Atlantic and Indian oceans were formed, presumably through the drifting of continents. Sea spread in Southern Europe and Northern Africa. Climate was tropical over much of the earth with glaciers covering only the tops of high mountains. Complex structures of flowering plants continued to develop. The earliest horse, camel, rhinoceros, pig, elephant, cattle and primitive apes (monkeys and gibbons) appeared.  3.Oligocene epoch The continents began to grow again. Mountain ranges continued to build up. A cycle of warm, midland cool seasons became established. Forests occupied less land, while grassland increased in area. Grass-eating mammals increased in number and variety. A primitive, tailless ape, probably the ancestor of humans appeared.  4.Miocene epoch Extensive movements of the Earth’s crust joined Asia with Europe and locked in the Mediterranean Sea. Extensive erosion started to carve Grand Canyon in North America. Climates were varied, warm in some parts and cooler in other parts. Trees that seasonally shed leaves increased in number and kind. More grasslands formed.  B) Quaternary period 1.Pleistocene epoch Glaciers and ice spread and receded several times during the epoch. The increase of glaciers lowered the ocean level; the melting of glaciers raised the ocean level. Mammals and primitive people crossed land bridges exposed by the sinking water level.  Determine whether the following statements are true or false. If it is false change the underlined words/phrase to make the statement true. Write your answer on a separate sheet. 1. Strata refers to the horizontal layers of igneous rock that contains different colors, textures, and fossils inside. True | False ____________________________________________________ 2. The geologic history of the Earth is broken up into hierarchical chunks of time. True | False_____________________________________________________ 3. Eons represent the longest portions of geologic time which include the present time. True | False_____________________________________________________ 4. The Precambrian represents more than 80 percent of the total geologic record and is preceded by the Phanerozoic eon. True | False _____________________________________________________ 5. The Cenozoic is the current and most recent of the three geological eras of the Phanerozoic Eon. True | False ____________________________________________________