3Fossils and Ancient Life Paleontologists are scientists who collect and study fossils.All information about past life is called the fossil record.The fossil record includes information about the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived.17-1
4Fossils are useful because . . . We can compare ancient organisms with today’s to see if organic evolution has occurred.
5The fossil record provides incomplete information about the history of life. Over 99% of all species that have lived on Earth have become extinct, which means that the species has died out.
6How Fossils FormFossils can be as large as a complete, preserved animal, or as small as a fragment.Most fossils form in sedimentary rock.Sedimentary rock forms when exposure to the elements breaks down existing rock into small particles of sand, silt, and clay.17-1
7How Fossils Form Fossil Formation The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.
8How Fossils FormThe fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.
9The fossil record provides evidence about the history of life on Earth The fossil record provides evidence about the history of life on Earth. Most fossil formed in sedimentary rock.
10What are the types of fossils? The fossil record provides evidence about the history of life on Earth. Most fossil formed in sedimentary rock.
15Interpreting Fossil Evidence Paleontologists determine the age of fossils using relative dating or radioactive dating.What information do relative dating and radioactive dating provide about fossils?17-1
16NO, not dating a relative. Relative DatingNO, not dating a relative.
17Relative DatingIn relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.Rock layers form in order by age—the oldest on the bottom, with more recent layers on top.17-1
36Through dating of rocks, scientists have been able to construct a timetable of earth’s history. Geologic time scale
37Geologic Time Scale Major divisions = Eras (e.g. “Age of Reptiles”)Eras divided into: Periods/Epochs(e.g. “Jurassic Period”)17-1
38Way older than your teacher. There is good evidence that earth is 4.5 to 5 billion years old.Way older than your teacher.
39ErasGeologists divide the time between Precambrian time and the present into three eras:Paleozoic EraMesozoic EraCenozoic Era17-1
40Geologic Time Scale The Paleozoic began about 544 million years ago. Many vertebrates and invertebrates lived during this time.17-1
41Geologic Time Scale Permian 290–245 360–290 Carboniferous 410–360 Devonian410–360The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.Silurian440–410Ordovician505–440Cambrian544–505
42Geologic Time Scale The Mesozoic began about 245 million years ago. Dinosaurs lived during this time.Mammals began to evolve during this era.17-1
43Cretaceous 145–65 Jurassic 208–145 Triassic 245–208 The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.Triassic245–208
44Geologic Time ScaleThe Cenozoic began about 65 million years ago and continues to the present.Mammals became common during the Cenozoic.17-1
45Geologic Time ScaleThe basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.
46PeriodsEras are subdivided into periods, which range in length from tens of millions of years to less than two million years.Many periods are named for places around the world where geologists first discovered the rocks and fossils of that period.
47Earth’s history is often compared to a familiar measurement, such as the twelve hours between noon and midnight. In such a comparison, notice that Precambrian Time lasts from noon until after 10:30 pm.
48Which of the following statements about fossils is NOT true? Most fossils form in sedimentary rock.Fossils occur in a particular order.Only a small portion of fossils are from extinct organisms.Fossils can be used in relative dating of rock formations.17-1
49The fossil record consistently shows evidence that all forms of life have existed in all geologic eras.living organisms have only been on Earth for a short time.living things have changed over time.ancient life-forms are much the same as forms found living today.17-1
50Index fossils assist paleontologists in dating rocks because they represent species that were widely distributed and existed for a very long time.existed in a single location for a short period of time.were widely distributed and existed for a short time.existed in a single location for a very long time.17-1
51Determining the age of a fossil by comparing its placement with fossils in other layers of rock is calledcarbon-14 dating.fossil-indexing.relative dating.absolute dating.17-1
52According to the geologic time scale, geologic time begins with Precambrian Time.the Paleozoic Era.the Quaternary Period.the Cambrian Era.17-1
54Patterns of evolution Evidence of mass extinctions: Many fossils are from species no longer living (extinct). Of all species that ever lived, < 1% exist today!Evidence of mass extinctions:Floods, comets, volcanic activity17-4