Chapter 16.1: Fossils


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Grade 8 Integrated Science Chapter 16 Lesson 1 on fossils. This lesson gives detail about fossil, how they form, and the different types. The purpose of this lesson is for students to understand fossil and how they give us a record of our planet's past. Students should know the different types of fossils by the end of the lesson.

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Chapter 16.1: Fossils

  1. 1. Fossils Chapter 16 Lesson 1 Pages 564 - 572
  2. 2. Vocabulary • Fossil – the preserved remains or evidence of ancient living things • Catastrophism – the idea that conditions and organisms on Earth change in quick, violent events • Uniformitarianism – a principle that states that geologic processes that occur today are similar to those that have occurred in the past • Carbon Film – the fossilized carbon outline of an organism or part of an organism • Mold – the impression in a rock left by an ancient organism • Cast – a fossil copy of an organism made when a mold of the organism is filled with sediment of mineral deposits • Trace Fossil – the preserved evidence of the activity of an organism • Paleontologist – scientists who study fossils
  3. 3. Evidence of the Distant Past • Just like old photos, fossils provide us with clues about Earth’s past • Fossils are the preserved remain or evidence of ancient living things
  4. 4. Catastrophism • Many fossils represent plants and animals that are extinct • In the past many scientists believed that a single, sudden, catastrophic disaster killed the organisms that become fossil • Catastrophism is the idea that conditions and organisms on Earth change in quick, violent events – These include large volcanic eruptions and widespread flooding
  5. 5. Catastrophism • Scientists eventually disagreed with catastrophism because Earth’s history is full of violent events • Most people who supported catastrophism thought that Earth was only a few thousand years old
  6. 6. Uniformitarianism • In the 1700s, James Hutton rejected the idea of catastrophism • Hutton thought that the processes responsible for changing the landscape could also shape Earth’s surface – For example, he thought that erosion caused by streams could also wear down mountains – He realized that these processes would take a long time and proposed that Earth was much older than a few thousand years
  7. 7. Uniformitarianism • Hutton’s ideas were eventually included in a principle called uniformitarianism. – The principle of uniformitarianism states that geological processes that occur today are similar to those that have occurred in the past – According to this view, Earth’s surface is constantly being reshaped in a steady, uniform manner
  8. 8. Uniformitarianism • Today, uniformitarianism is the basis for understanding Earth’s past • But scientists also know that catastrophic event do sometimes occur – Huge volcanic eruptions and giant meteorite impacts can change Earth’s surface quickly and can be explained by natural processes
  9. 9. Fossil Formation • Not all dead organisms become fossils. More than likely, you will not become a fossil. • Fossils form only under certain conditions.
  10. 10. Conditions for Fossil Formation • Most plants and animals are eaten or decay when they die, leaving no trace that they ever lived – Consider an apple. More than likely an apple will decay into a soft lump and be decomposed by bacteria and insects • Some conditions increase the chances that a fossil will form. 1. If the organism has hard parts, such as shells, teeth, or bones 2. If the organism is buried quickly after it dies. • This way the layers of sand and mud slow or stop decay
  11. 11. Fossils Come in All Sizes • Many of the fossils we think of are large dinosaur fossils. • However, not all fossils are large. • Microfossils are tiny fossils each about the size of a speck of dust. – Details of microfossils can be seen only under a microscope
  12. 12. Types of Preservation • Fossil are preserved in many different ways: – Preserved Remains – Carbon Films – Mineral Replacement – Molds – Casts – Trace Fossils
  13. 13. Preserved Remains • Sometimes the actual remains of organisms are preserved as fossils • For this to happen, an organism must be completely enclosed in some material over a long period of time. – This would prevent it from being exposed to air or bacteria – Generally this fossils are less than 10,000 years old. However insects preserved in amber can be millions of years old.
  14. 14. Carbon Films • Sometimes when an organism is buried, exposure to heat and pressure forces gases and liquids out of the organism’s tissues. • This leaves only the carbon behind • A carbon film is the fossilized carbon outline of an organism or part of an organism
  15. 15. Mineral Replacement • Replicas, or copies, of organisms can form from minerals in groundwater. • They fill in the pore spaces or replace the tissues of dead organisms • Petrified wood is an example
  16. 16. Molds • Sometimes all that remains of an organism is its fossilized imprint or impression. • A mold is the impression in a rock left by an ancient organism 1. First, sediment must harden around a buried organism 2. As the organism decays over time an impression of its shape remains in the sediment 3. Eventually the sediment turns into rock
  17. 17. Casts • Sometimes, after a mold forms, it is filled with more sediment,. • A cast is a fossil copy of an organism made when a mold of the organism is filled with sediment or mineral deposits. Mold Cast
  18. 18. Trace Fossils • Some animals leaves fossilized traces of their movement or activity • A trace fossil is the preserved evidence of the activity of an organism • These include – Tracks – Footprints – Nest – Droppings • These fossils help scientists learn about characteristics and behaviors of animals – They can reveal clues about an organism’s size, speed, and whether they traveled alone or in groups
  19. 19. Ancient Environments • Scientists who study fossils are called paleontologists • Paleontologists use the principle of uniformitarianism to learn about ancient organisms and their environment • They often compare fossils of ancient organisms to organisms living today – For example, trilobite fossil and horseshoe crabs look alike – Horseshoe crabs today live in shallow water on the ocean floor – Partly because trilobite fossils look so much like horseshoe crabs, paleontologists infer that trilobites also lived in shallow ocean waters
  20. 20. Shallow Seas • Today, Earth’s continents are mostly above sea level. • But, sea level has risen, flooding Earth’s continents, many times in the past • For example, a shallow ocean covered much of North America 450 million years ago. • Fossils of organisms that lived in that shallow ocean help scientists reconstruct what the seafloor looked like at that time.
  21. 21. Past Climates • Evidence indicates that Earth's present-day climate is warming. • Fossils show that Earth's climate has warmed and cooled many times in the past • Plant fossils are especially good indicators of climate change • For example, fossils of ferns and other tropical plants dating to the time of the dinosaurs reveal that Earth was very warm 100 million years ago • Tropical forests and swamps covered much of the land • Millions of year later, the swamps and forests were gone, but coarse grasses grew in their place
  22. 22. Past Climates • Huge sheets of ice called glaciers spread over parts of N. America, Europe, and Asia. • Fossils suggest that some species that lived during this time, such as the woolly mammoth were able to survive in the colder climate