Slide 1 of 40 The Fossil Record

Slide 2 of 40 Fossils and Ancient Life What are fossils? What are fossils? Preserved remains of ancient organisms Preserved remains of ancient organisms Fossil record includes information about: 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. the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived. It also shows how different groups of organisms, including species, have changed over time. It also shows how different groups of organisms, including species, have changed over time. How are fossils formed? How are fossils formed? Dead organisms are buried by sediments, if conditions are perfect, they are persevered Dead organisms are buried by sediments, if conditions are perfect, they are persevered Water carries small rock particles to lakes and seas Water carries small rock particles to lakes and seas Dead organisms are buried by layers of sediment, which forms new rock Dead organisms are buried by layers of sediment, which forms new rock The preserved remains may be later discovered and studied. The preserved remains may be later discovered and studied.

Slide 3 of 40 Fossils and Ancient Life Why is the fossil record incomplete? Why is the fossil record incomplete? It takes perfect conditions to make fossils, so many organisms were never persevered It takes perfect conditions to make fossils, so many organisms were never persevered Over 99% of all species that have lived on Earth have become extinct, which means that the species has died out. Over 99% of all species that have lived on Earth have become extinct, which means that the species has died out. All information about past life is called the fossil record. All information about past life is called the fossil record.

Slide 4 of 40 How Fossils Form How Fossils Form How Fossils Form Fossils can be as large as a complete, preserved animal, or as small as a fragment. Fossils can be as large as a complete, preserved animal, or as small as a fragment. Most fossils form in sedimentary rock. 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. Sedimentary rock forms when exposure to the elements breaks down existing rock into small particles of sand, silt, and clay.

Slide 5 of 40 Interpreting Fossil Evidence Interpreting Fossil Evidence Interpreting Fossil Evidence Paleontologists (scientists who collect and study fossils) determine the age of fossils using relative dating or radioactive dating. Paleontologists (scientists who collect and study fossils) determine the age of fossils using relative dating or radioactive dating.

Slide 6 of 40 Relative Dating In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock. In 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. Rock layers form in order by age—the oldest on the bottom, with more recent layers on top. By using this information from rock formations in various parts of the world scientists have been able to establish the geologic time scale. By using this information from rock formations in various parts of the world scientists have been able to establish the geologic time scale.geologic time scalegeologic time scale Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils. Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils.

Slide 7 of 40 Relative Dating – Index Fossils Each fossil is an index fossil. It enables us to date the rock layer in which it is found. We use a collection of rocks from different locations. Each fossil is an index fossil. It enables us to date the rock layer in which it is found. We use a collection of rocks from different locations. An index fossil is a species that is recognizable and that existed for a short time but had a wide geographic range. An index fossil is a species that is recognizable and that existed for a short time but had a wide geographic range.

Slide 8 of 40 Radioactive Dating and Half Life Radioactive Dating and Half Life Radioactive Dating Radioactive Dating Scientists use radioactive decay to assign ages to rocks. Scientists use radioactive decay to assign ages to rocks. Some elements are radioactive and steadily break down. Some elements are radioactive and steadily break down. Half Life Half Life Radioactive dating is the use of half-lives to determine the age of a sample. Radioactive dating is the use of half-lives to determine the age of a sample. A half-life is the length of time required for half of the radioactive atoms in a sample to decay. A half-life is the length of time required for half of the radioactive atoms in a sample to decay. After 1 half-life: ½ atoms remain After 1 half-life: ½ atoms remain After 2 half-lives: ½ x ½ = ¼ atoms remain After 2 half-lives: ½ x ½ = ¼ atoms remain After 3 half-lives: ½x ½ x ½ = ⅛ atoms remain After 3 half-lives: ½x ½ x ½ = ⅛ atoms remain After n half-lives: ½ n atoms remain After n half-lives: ½ n atoms remain Different elements have different half-lives Different elements have different half-lives

Slide 9 of 40 In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains. In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains. Such measurements enable scientists to determine the absolute age of rocks and the fossils they contain. Radioactive Dating and Half Life Radioactive Dating and Half Life

Slide 10 of 40 Geologic Time Scale Paleontologists use a scale called the geologic time scale to represent evolutionary time. Paleontologists use a scale called the geologic time scale to represent evolutionary time. Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide. Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide. The basic divisions of the geologic time scale are eras and periods. The basic divisions of the geologic time scale are eras and periods. Periods Periods Eras are subdivided into periods, which range in length from tens of millions of years to less than two million years. Eras 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. Many periods are named for places around the world where geologists first discovered the rocks and fossils of that period.

Slide 11 of 40 Geologic Time Scale Geologic time begins with Precambrian Time, which covers about 88% of Earth’s history. Geologic time begins with Precambrian Time, which covers about 88% of Earth’s history. Vendian 650–544

Slide 12 of 40 Geologic Time Scale Eras Eras Geologists divide the time between Precambrian time and the present into three eras: Geologists divide the time between Precambrian time and the present into three eras: Paleozoic Era Paleozoic Era Mesozoic Era Mesozoic Era Cenozoic Era Cenozoic Era Permian Carboniferous Devonian Silurian Ordovician Cambrian 290– – – – – –505

Slide 13 of 40 Geologic Time Scale The Mesozoic began about 245 million years ago. The Mesozoic began about 245 million years ago. Dinosaurs lived during this time. Dinosaurs lived during this time. Mammals began to evolve during this era. Mammals began to evolve during this era.

Slide 14 of 40 Geologic Time Scale Cretaceous Jurassic Triassic 145–65 208– –208

Slide 15 of 40 Geologic Time Scale The Cenozoic began about 65 million years ago and continues to the present. The Cenozoic began about 65 million years ago and continues to the present. Mammals became common during the Cenozoic. Mammals became common during the Cenozoic.

Slide 16 of 40 Geologic Time Scale

Slide 17 of 40 End

Slide 18 of 40 Which of the following statements about fossils is NOT true? Which of the following statements about fossils is NOT true? Most fossils form in sedimentary rock. Most fossils form in sedimentary rock. Fossils occur in a particular order. Fossils occur in a particular order. Only a small portion of fossils are from extinct organisms. Only a small portion of fossils are from extinct organisms. Fossils can be used in relative dating of rock formations. Fossils can be used in relative dating of rock formations.

Slide 19 of 40 The fossil record consistently shows evidence that The fossil record consistently shows evidence that all forms of life have existed in all geologic eras. all forms of life have existed in all geologic eras. living organisms have only been on Earth for a short time. living organisms have only been on Earth for a short time. living things have changed over time. living things have changed over time. ancient life-forms are much the same as forms found living today. ancient life-forms are much the same as forms found living today.

Slide 20 of 40 Index fossils assist paleontologists in dating rocks because they represent species that Index fossils assist paleontologists in dating rocks because they represent species that were widely distributed and existed for a very long time. were widely distributed and existed for a very long time. existed in a single location for a short period of time. existed in a single location for a short period of time. were widely distributed and existed for a short time. were widely distributed and existed for a short time. existed in a single location for a very long time. existed in a single location for a very long time.

Slide 21 of 40 Determining the age of a fossil by comparing its placement with fossils in other layers of rock is called Determining the age of a fossil by comparing its placement with fossils in other layers of rock is called carbon-14 dating. carbon-14 dating. fossil-indexing. fossil-indexing. relative dating. relative dating. absolute dating. absolute dating.

Slide 22 of 40 According to the geologic time scale, geologic time begins with According to the geologic time scale, geologic time begins with Precambrian Time. Precambrian Time. the Paleozoic Era. the Paleozoic Era. the Quaternary Period. the Quaternary Period. the Cambrian Era. the Cambrian Era.