Chapter 8 Study Guide Answers – Flashcards
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The preserves, remains, or traces of an organism.
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What is a fossil?
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When living things die and are buried by sediments.
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How do most fossils form?
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Palenotologists, remains, simpler
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The fossil record shows that life on Earth has changed of time.____ have found that older rocks contain____of organisms that are_____ than those alive today.
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evolution
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The process by which all the diffrent kinds of living things have changed over long periods of time is called_____.
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petrified fossil
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A fossil formed when minerals replace all or part of an organism is called____.
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trace fossils
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Which type of fossil can provide clues about the activities of ancient organisms?
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age, ages, rocks
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The relative age of a rock is its_____ compared to the______ of other______.
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in horizontal layers; young on top and old on bottom.
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The law of superposition states____________.
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Index fossils
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The fossils of organisms that were widely distributed but only lived during a shorter period of time are called____.
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They tell the relative age of rocks.
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Why are index fossils useful to geologists?
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unstable, another
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Radioactive decay occurs when atoms of an______element break down to form atoms of __________element
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half-life
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The time it takes for half of the radioactive atoms in a sample of radioactive element to decay is the element's_______.
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The absolute age of rocks.
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Radioactive dating enables geologists to determine______.
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Igneous
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Radioactive dating works best with what rocks?
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relative dating
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Originally, the geologic time scale placed Earth's rocks in order by_______.
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The life forms and geological events in history.
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The geologic time scale is a record of________.
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eras
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The Paleozoic, Mesozoic, and Cenozoic are divisions in the geologic time scale called____.
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periods
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The Mesozoic era is divided into the Triassic, the Jurassic, and the Cretaceous. These divisions of the geologic time scale are called _____.
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Earth forming
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Precambrian Time, which includes most of Earth's history, began with _______.
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Pangea
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About 260 million years ago, Earth's continents moved together to form the supercontinent called_____.
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Ice Age
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How did the Earth change about 2.5 billion years ago when many organisms began using photosynthesis to make food?
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mammals
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The Cenozoic era is often called the age of ______.
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extict
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A type of organism that no longer exists on Earth is said to be ______.
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Carbon Films
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In which type of fossil might you find the remains of an insect preserved with little or no change?
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no mammals/reptiles
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How would Earth be different if its surface had never cooled during early Precambrian Time?
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newer
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What is the age of an intrusion of igneous rock in relation to the sedimentary rock layer through which it passes?
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reptiles, mammals
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During the Cambrian Explosion that began the Paleozoic Era, the many new forms of life that evolved were _______.
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bacteria
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During the Devonian Period, animals that could live on land began to evolve. These animals still spent part of their lives in the water. What were these animals called?
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volcanic activity or a large object from space
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What do most scientists think caused the mass extinction of dinosaurs and other organisms at the end of the Cretaceous Period?
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Precambrian Times
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Earth's atmosphere, oceans, and continents began to form during the first several million years of _____.
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sedimentary
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Fossils usually occur in _____ rock.
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trace fossils
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Footprints in trails are examples of ________.
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relative
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The law of superposition helps geologists determine the _____ age of the rock layer.
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evolution
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At the beginning of the Paleozoic Era, a great number of different types of organism evolved in an event called the _____.
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younger
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Rock layers are always _____ than the faults that cut across them.
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eras
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Geologists divide Earths long history into small units that make up the ______.
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Cenozoic
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On the geologic time scale, the Mesozoic Era is the _______.
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Paleozoic
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Life on Earth first appeared during the _______.
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bone
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Generally, the only _______ parts of organisms become fossils.
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fossils
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Paleontologists are scientists who study ______.
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rocks
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Scientists know how groups of animals change over time by studying information contained in the _______.
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petrified
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A _________ fossil forms when dissolved minerals replace the remains of an organism and then harden to form rock.
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carbon film
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Plant leaves many form a fossil called a _____, a thin layer of carbon on rock.
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period
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On the geologic time scale, the Mesozoic Era is divided into the Triassic, Jurassic, and Cretaceous ______.
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extinct
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Organisms, such as dinosaurs, that no longer exist and will never again live on Earth are said to be _______.
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relative
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A rock layer's _____ age is its age compared to the ages of other rock layers.
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trace
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A certain ammonites are used as ______ fossils because they lived in many different areas but for only a brief time.
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geological time
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A _____ is a gap in the geologic record where some rock layers have been lost because of erosion.
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radioactive
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The breakdown of unstable carbon-14 to form stable nitrogen-14 is an example of ______ decay.
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intrusion
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Potassium-40 is useful for dating very old rocks because it has a _____ of 1.3 billion years.
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Carbon- 14
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Geologists use the radioactive element ________ to determine the age of organic remains, such as bone.
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half-life
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The time it takes for one half of the atoms in a sample of a radioactive element to decay is called the elements ________.
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Precambrian
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Geologic time begins with the long span of time called _______ Time
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Quaternary
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The present day is part of the _________ Era.
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vertebrates
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Jawless fish were Earth's first _______, or animals with backbones
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Ice Age
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During the Quaternary Period, a series of ______ occurred when Earth's climate cooled.
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crust
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The mass extinction at the end of the Paleozoic Era may have occurred because Earth's ______ moved together into one large landmass, changing Earth's climate.
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mammals
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The extinction of the dinosaurs gave warm-blooded vertebrates called ______ a chance to become abundant.
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4.6 billion
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Scientists hypothesize that Earth formed at the same time as the other planets and the sun, roughly ______ years ago.
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Jurassic
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Reptiles, such as dinosaurs, were so successful during the _______ Era that this time is often called the Age of Reptiles.
