Index Fossils Handouts PDF

Index Fossils? After going through this module, you are expected to: 1. define what is index fossils or guide fossils and subdivisions of geologic time scale. 2. identify how index fossils are used to described subdivisions of geologic time sc...

Index Fossils? After going through this module, you are expected to: 1. define what is index fossils or guide fossils and subdivisions of geologic time scale. 2. identify how index fossils are used to described subdivisions of geologic time scale. 3. explain why it is rare for an organism to be preserved as a fossil. 4. distinguish the difference between body fossils and trace fossils. 5. describe five types of fossilization and what a living fossil is. 6. value the importance of index fossils and give several examples. 7. explain how the fossil record shows us that species evolve over time. 8. describe the general development of Earth’s life forms over the last 540 million years Article about Index fossils. A fossil is the remain or evidence of a living thing. The most common fossils are bones, skills, teeth, leaves, spores, and seeds of pollen grains. Most fossils are formed when the whole part of an organism becomes buried in sedimentary rocks, which provide the most important evidence about the evolution of plants and animals. Fossils give clues about organisms that lived long ago. They also provide evidence about how Earth’s surface changed overtime. Fossils helps scientist understand what past environments may have been like. There are five main types of fossils namely: 1) Petrified fossils are formed through petrification that means turning into stones. It forms when minerals replace all part of an organism. 2) Molds and casts form when hard parts of an organism are buried in sediments such as sand, silt, or clay. A cast is formed as the result of mold. Minerals and sediments fill the mold’s empty spaces and make a cast. (3) Carbon Films, all living things contain an element called carbon. When an organism dies and is buried in sediments, the material that make up the organism break down. Eventually, only carbon remains. (4) Trace fossils show the activities of organism. An animal makes a footprint when it steps in sand or mud. Overtime the footprint is buried in layers of sediment, then sediment becomes solid rock. (5) Preserved remains, and some organisms get preserved in or close to their original states. There are some ways it can happen;(a) Amber-an organism, such as insect, is trapped in a tree’s sticky resins and dies. (b) Tar an organism, such as mammoth, is trapped in a tar pit and dies. (c) Ice-an organism, such as wooly mammoth, dies in very cold regions. Definition of terms: A fossil is any remains of ancient life. It can be body fossils which are remains of the organism itself, or trace fossils, such as burrows, tracks, or other evidence of activity. Preservation as a fossil is a relatively rare process. The chances of becoming a fossil are enhanced by quick burial and the presence of preservable hard parts, such as bones or shells. Fossils form in five ways: preservation of original remains, permineralization, molds and casts, replacement, and compression. Rock formations with exceptional fossils are called very important for scientists to study. They allow us to see information about organisms that we may not otherwise ever know. Index fossils are fossils that are widespread but only existed for a short period. Index fossils help scientists to find the relative age of a rock layer and match it up with other rock layers. Living fossils are organisms that haven’t changed much in millions of years and are still alive today. Fossils give clues about the history of life on Earth, environments, climate, movement of plates, and other events. Adaptations are favorable traits that organisms inherit. Adaptations develop from variations within a population and help organisms to survive in their given environment. Changes in populations accumulate over time; this is called evolution. The fossil record shows us that present-day life forms evolved from earlier different life forms. It shows us that the first organisms on Earth were simple bacteria that dominated the Earth for several billion years. Beginning about 540 million years ago more complex organisms developed on Earth. During the Phanerozoic Eon, all the plant and animal types we know today have evolved. Many types of organisms that once lived are now extinct. Earth’s overall environment, especially the climate, has changed many times, and organisms change too over time. Fossils Throughout human history, people have discovered fossils and wondered about the creatures that lived long ago. The griffin, a mythical creature with a lion’s body and an eagle’s head and wings, was probably based on skeletons of Protoceratops that were discovered by nomads in Central Asia. (Figure 1.1) Figure 1.1. Skeletons of Protoceratops Another fossil reminded the Greeks of the coiled horns of a ram. The Greeks named them ammonites after the ram god Ammon. Similarly, legends of the Cyclops may be based on fossilized elephant skulls found in Crete and other Mediterranean islands. Can you see why? (Figure 1.2)  Figure 1.2. Ammonite (left) and elephant skull (right) The giant pterosaur Quetzalcoatlus had a wingspan of up to 12 meters (39 feet). The dinosaur Argentinosaurus had an estimated weight of 80,000 kg, equal to the weight of seven elephants! Other fossils, such as the trilobite and ammonite, impress us with their bizarre forms and delicate beauty.  Figure 1.3. Kolihapeltis (left) and Ammonite (right) Clues from Fossils Fossils are our best form of evidence about the history of life on Earth. In addition, fossils can give us clues about past climates, the motions of plates, and other major geological events. The first clue that fossils can give is whether an environment was marine (underwater) or terrestrial (on land). Along with the rock characteristics, fossils can indicate whether the water is shallow or deep and whether the rate of sedimentation is slow or rapid. Fossils can also reveal clues about past climate. For example, fossils of plants and coal beds have been found in Antarctica. Although Antarctica is frozen today, in the past it must have been much warmer. How are index fossils formed? Index fossils are the preserved remains of specific species found in the strata of sedimentary rock. They are easily recognized by shape and lived for either a short period, geologically speaking, or completely vanished from the Earth in a known extinction event. Index fossils are usually sea creatures due to preservation conditions and how widespread ocean-dwelling creatures can proliferate on the planet. Types of Fossils Fossilization can occur in many ways. Most fossils are preserved in one of five processes; preserved remains, permineralization, molds and casts, replacement, and compression. 1. Preserved Remains The rarest form of fossilization is the preservation of original skeletal material and even soft tissue. For example, insects have been preserved perfectly in amber, which is ancient tree sap. Several mammoths and even a Neanderthal hunter have been discovered frozen in glaciers. 2. Permineralization The most common method of fossilization is permineralization. After a bone, wood fragment, or shell is buried in sediment, it may be exposed to mineral-rich water that moves through the sediment. This water will deposit minerals into empty spaces, producing a fossil. Fossil dinosaur bones, petrified wood, and many marine fossils were formed by permineralization. 3. Molds and Casts In some cases, the original bone or shell dissolves away, leaving behind a space in the shape of the shell or bone. This depression is called mold. Later the space may be filled with other sediments to form a matching cast in the shape of the original organism. Many mollusks (clams, snails, octopi, and squid) are commonly found as molds and casts because their shells dissolve easily. 4. Replacement In some cases, the original shell or bone dissolves away and is replaced by a different mineral. For example, shells that were originally calcite may be replaced by dolomite, quartz, or pyrite. If quartz fossils are surrounded by a calcite matrix, the calcite can be dissolved away by acid, leaving behind an exquisitely preserved quartz fossil. 5. Compression Some fossils form when their remains are compressed by high pressure. This can leave behind a dark imprint on the fossil. Compression is most common for fossils of leaves and ferns but can occur with other organisms, as well. (A) (B) (C) (D) (E) Figure 1.4. Five types of fossils Insect preserved in (A) amber, (B) petrified wood, (C)cast and mold of a clamshell, (D)compression fossil of a fern, and (E)pyritized ammonite. Exceptional Preservation  Some rock beds have produced exceptional fossils. Fossils from these beds may show evidence of soft body parts that are not normally preserved. Two of the most famous examples of soft organism preservation are the Burgess Shale in Canada and the Solnhofen Limestone in Germany. Figure 1.5. Fossils from Lagerstätten: Archaeopteryx (left) and Anomalocaris (right). Archaeopteryx was an early bird. Anomalocaris was an enormous predator (one meter long) that lived 500 million years ago. Index fossils are widespread but only existed for a relatively brief period. When a particular index fossil is found, the relative age of the bed is immediately known. Ammonites, trilobites, and graptolites are often used as index fossils, as are various microfossils, or fossils of microscopic organisms. Living fossils are organisms that have existed for a tremendously long period without changing very much at all. For example, the Lingulata brachiopods have existed from the Cambrian period to the present, a period of over 500 million years! Figure 1.6. Fossil Lingula (left) and modern Lingula (right) Correlation by Index Fossils To be considered an index fossil, it must meet 3 criteria: 1. The fossilized organism must be easily recognizable. It must be easy to ID and look unique. 2. The fossils must be geographically widespread or found over large areas so that we can use them to match  layers separated by huge distances. 3. The fossil must have lived for only a short time so that it appears in only a horizontal layer of sedimentary rocks. Example: The diagram shows several rocks outcrops separated by large distances. In each outcrop are several fossils. Which of the fossils shown is an index fossil? When choosing the right index fossil, we can reinterpret the characteristics of index fossil to help us as stated above: To find the index fossil you must eliminate any fossils that don’t show up in each rock outcrop and those that show up in more than one layer per outcrop. Index Fossils and Living Fossils We can eliminate “Fossil 1” because it shows up in multiple layers in the same outcrop. (It lived for too long of a time in Earth’s history to help establish dates of other rocks). We can eliminate “Fossil 2” because it shows up in multiple layers in Column 2. (It lived for too long a time). We can eliminate “Fossil 3” because it is only in one layer in one outcrop. After we've eliminated all the fossils that don't fit the requirements, we have only 1 left that appears in all the outcrops, and only one layer  per outcrop. So, the correct index fossil is: Using Index Fossils to Correlate Rock Layer We can use index fossils and key beds to correlate or match rock layers with the same age. By doing this, we can then place other layers of rocks in order of their relative ages to find the oldest and youngest rocks in a series of outcrops. Example: Examine the outcrop and determine which layers are the oldest and youngest? To find the oldest and youngest layers in the entire diagram, we first must correlate the three outcrops. We can do this by using the trilobite index fossil because it appears in all three outcrops. By correlating them, we now know that layers A, K, and Q are of the same age. So, to find the oldest rocks we look below them, and to find the youngest rocks we look above them. If we create a chart building our way up and down by looking directly above and below each layer, we will find the top and Charles Doolittle Walcott was a paleontologist, a scientist who studies past life on Earth. He was searching for fossils. Riding on horseback, he was making his way down a mountain trail when he noticed something on the ground. He stopped to pick it up. It was a fossil! One of the organisms preserved in the fossils had a soft body like a worm, five eyes, and a long nose like a vacuum cleaner hose. Figure 2:1. This bizarre animal with five eyes lived during the Cambrian. The organisms in Walcott’s fossils lived during a time of geologic history known as the Cambrian. The Cambrian period began about 540 million years ago. It marked the beginning of the Phanerozoic Eon. It also marked the beginning of many new and complex life forms appearing on Earth. In fact, the term Phanerozoic means “time of well-displayed life.” We still live today in the Phanerozoic Eon. However, life on Earth is very different today than it was 540 million years ago.  Figure 2.2. Diversity of organisms on Earth. There are over 1 million species of plants and animals known to be currently alive on Earth. (Figure 12.2) Look around you and notice that the organisms on this planet have incredible variation. One of the most remarkable features of Earth’s organisms is their ability to survive in their specific environments. For example, polar bears have thick fur coats that help them stay warm in the icy waters that they hunt in. Figure 2.3. Polar bear Other organisms have special features that help them hunt for food or avoid being the food of another organism. For example, when zebras in a herd run away from lions, the zebras’ dark stripes confuse the lions and make it hard for them to focus on just one zebra during the chase. Hummingbirds have long thin beaks that help them drink nectar from flowers. Some plants have poisonous or foul-tasting substances in them that keep animals from eating them. Adaptations and Evolution The characteristics of an organism that help it survive in each environment are called adaptations. Adaptations develop when certain variations in a population help some members survive better than others. Often the variation comes from a mutation or a random change in an organism’s genes. The ones that survive pass favorable traits on to their offspring.  Figure 2.4. Adaptations and Evolution Changes and adaptations in a species accumulate over time. Eventually, the descendants are very different from their ancestors and may become a whole new species. Changes in a species over time are called evolution. It shows us that many of the life forms that live today developed from earlier, different life forms. For example, horse fossils show us that about 60 million years ago horses were much smaller than they are today (Figure 12.5). Fossils also show us that horses’ teeth and hooves have changed several times as horses have adapted to changes in the environment. Studying the Fossil Record Figure 2.5. Horse Like the organisms that were represented in Walcott’s fossils, many of the organisms that once lived on Earth are now extinct. Earth’s overall environmental conditions have changed many times since the Cambrian, and many organisms did not have the traits to survive the changes. Those that did survive the changes passed traits on to their offspring. They gave rise to the species that live today. We study fossils to learn about how species responded to change over the Earth’s long history. Fossils show us that simple organisms dominated life on Earth for its first 3 billion years. Then, between 1 and 2 billion years ago, the first multi-cellular organisms appeared on Earth. Life forms gradually evolved and became more complex. During the Cambrian period, animals became more diverse and complex. Phanerozoic Eon The Phanerozoic Eon is divided into three chunks of time called eras—the Paleozoic, the Mesozoic, and the Cenozoic Table (1). They span from about 540 million years ago to the present. We now live in the Cenozoic Era. The table below shows how life has changed during the long span of the Phanerozoic Eon. Notice that different types of organisms developed at different times. However, all organisms evolved from a common ancestor. Life gradually became more diverse and new species branched out from that common ancestor. Most modern organisms evolved from species that were now extinct. Table 1. Development of Life During the Phanerozoic Eon Er Millions of Years Major Forms of Life a Ago Cenozoic 0.2 (200,000 years First humans ago) 35 First grasses; grasslands begin to dominate land Mesozoic 130 First plants with flowers 150 First birds on Earth 200 First mammals on Earth  251 Age of dinosaurs begins Paleozoic 300 First reptiles on Earth 360 First amphibians on Earth 400 First insects on Earth 475 First reptiles on Earth 500 First amphibians on Earth The eras of the Phanerozoic Eon are separated by events called mass extinctions. A mass extinction occurs when large numbers of organisms become extinct in a short amount of time. Between the Paleozoic and the Mesozoic, nearly 95% of all species on Earth died off. Between the Mesozoic and the Cenozoic, about 50% of all animal species on Earth died off. This mass extinction, 65 million years ago, is the one in which the dinosaurs became extinct. Earth’s climate changed numerous times during the Phanerozoic Eon. Just before the beginning of the Phanerozoic, much of the Earth was cold and covered with glaciers. Figure 2.6. Glacier The Phanerozoic began, however, the climate was changing to a warm and tropical one. (Figure 12.7) The glaciers were replaced with tropical seas. This allowed the Cambrian Explosion of many new life forms on Earth. During the Phanerozoic, Earth’s climate has gone through at least 4 major cycles between times of cold glaciers and times of warm tropical seas.  Figure 12.7. Tropical Changes 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 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. That law has never changed, so the rock must have formed near the sea. The rock maybe millions of years old, but the fossils in it serve as a clue for us today about how it was 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 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 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 ground. The place where you live right now may look very different in the far future. Every fossil tells us something about the age of the rock it's found in, and index fossils are the ones that tell us the most. Index fossils (also called key fossils or type fossils) are those that are used to define periods of geologic time. Characteristics of an Index Fossil A good index fossil is one with four characteristics: it is distinctive, widespread, abundant, and limited in geologic time. Because most fossil-bearing rocks formed in the ocean, the major index fossils are marine organisms. Boom-And-Bust Organisms Any type of organism can be distinctive, but not so many are widespread. Many important index fossils are of organisms that start life as floating eggs and infant stages, which allowed them to populate the world using ocean currents. The most successful of these became abundant, yet at the same time, they became the most vulnerable to environmental change and extinction. Trilobites, Hard-Shelled Invertebrates Consider trilobites, a very good index fossil for Paleozoic rocks that lived in all parts of the ocean. Trilobites were constantly evolving new species during their existence, which lasted 270 million years from Middle Cambrian time to the end of the Permian Period, or almost the entire length of the Paleozoic. Because they were mobile animals, they tended to inhabit large, even global areas. They were also hard- shelled invertebrates, so they fossilized easily. These fossils are large enough to study without a microscope. Small or Microscopic Fossils Other major index fossils are small or microscopic, part of the floating plankton in the world ocean. These are handy because of their small size. They can be found even in small bits of rock, such as wellbore cuttings. Because their tiny bodies rained down all over the ocean, they can be found in all kinds of rocks. Terrestrial Rocks For terrestrial rocks, which form on land, regional or continental index fossils may include small rodents that evolve quickly, as well as larger animals that have wide geographic ranges. These form the basis of provincial time divisions. Defining Ages, Epochs, Periods, and Eras Index fossils are used in the formal architecture of geologic time for defining the ages, epochs, periods, and eras of the geologic time scale. Some of the boundaries of these subdivisions are defined by mass extinction events, like the Permian Triassic extinction. The evidence for these events is found in the fossil record wherever there is a disappearance of major groups of species within a geologically short amount of time. Geologic Time Scale Today, the geologic time scale is divided into major chunks of time called eons. Eons may be further divided into smaller chunks called eras, and each era is divided into periods. We now live in the Phanerozoic eon, the Cenozoic era, and the Quaternary period. Sometimes, periods are further divided into epochs, but they are usually just named “early” or “late”, for example, “late Jurassic”, or “early Cretaceous.” Note that chunks of geologic time are not divided into equal numbers of years. Instead, they are divided into blocks of time when the fossil record shows that there were similar organisms on Earth. One of the first scientists to understand geologic time was James Hutton. In the late 1700s, he traveled around Great Britain and studied sedimentary rocks and their fossils. He believed that the same processes that work on Earth today formed the rocks and fossils from the past. He knew that these processes take a very long time, so the rocks must have formed over millions of years. He is sometimes called the “Father of Geology.” Figure 3.1 shows you a different way of looking at the geologic time scale. It shows how Earth’s environment and life forms have changed. Figure 3.1. Sample of a Geologic Time Scale A fossil is any remains of ancient life. Fossils can be body fossils, which are remains of the organism itself, or trace fossils, such as burrows, tracks, or other evidence of activity. Preservation as a fossil is a relatively rare process. The chances of becoming a fossil are enhanced by quick burial and the presence of preservable hard parts, such as bones or shells. Fossils form in five ways: preservation of original remains, permineralization, molds and casts, replacement, and compression.  Rock formations with exceptional fossils are called very important for scientists to study. They allow us to see information about organisms that we may not otherwise ever know. Index fossils are fossils that are widespread but only existed for a short period. Index fossils help scientists to find the relative age of a rock layer and match it up with other rock layers. Living fossils are organisms that haven’t changed much in millions of years and are still alive today. Fossils give clues about the history of life on Earth, environments, climate, movement of plates, and other events. Adaptations are favorable traits that organisms inherit. Adaptations develop from variations within a population and help organisms to survive in their given environment. Changes in populations accumulate over time; this is called evolution. The fossil record shows us that present-day life forms evolved from earlier different life forms. It shows us that the first organisms on Earth were simple bacteria that dominated the Earth for several billion years. Beginning about 540 million years ago, more complex organisms developed on Earth. During the Phanerozoic Eon, all of the plant and animal types we know today have evolved. Many types of organisms that once lived are now extinct. Earth’s overall environment, especially the climate, has changed many times, and organisms change too over time. Activity 2 A. Match the types of fossils in Column A with their description in column B. Write the letter of the correct answer on a separate sheet of paper. COLUMN A COLUMN B 1. PERTIFIED FOSSIL A. Some organisms get preserved in or close to their original states.  2. MOLDS AND CAST B. All living things contain an element called carbon. 3. CARBON FILMS C. Minerals and sediments that are left in the mold make a cast. 4. TRACE FOSSILS D. It is formed when minerals replace all or part of an organism. 5. PRESERVED REMAINS E. An animal makes a footprint when it steps in sand or mud. Activity 3: “Fill Me Up” Fill in the blank and choose your answer in the box provided. Write your answer on a separate paper. preserved remains past climates sedimentary rock motions of plates permineralization replacement molds and casts major geological events Compression microfossils must be easily adaptations recognizable Fossilization lived for only a short time mass extinction Living fossils geographically widespread variation 1. Fossils are our best form of evidence about the history of life on Earth, in addition, fossils can give us clues about , , and. 2. Index fossils are the preserved remains of specific species found in the strata of. 3. Most fossils are preserved in one of five processes; , , , and ,. 4. Ammonites, trilobites, and graptolites are often used as index fossils, as are various , or fossils of microscopic organisms. 5. are organisms that have existed for a tremendously long period of time without changing very much at all. 6. To be considered an index fossil, it must meet 3 criteria: The fossilized organism (1). (2). (3). 7. The process of a once living organism becoming a fossil is called. 8. An amazing diversity of organisms on Earth and it is called as. 9. The characteristics of an organism that help it survive in each environment are called. 10. The eras of the Phanerozoic Eon are separated by events called.