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Studying Fossils

Studying Fossils. Fossils. Fossils are preserved remains or traces of living things. Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shape of the organisms. Fossils. Scientists who study fossils are

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Studying Fossils

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  1. Studying Fossils

  2. Fossils • Fossilsare preserved remains or traces of living things. • Most fossils form when living things die and are buried by sediments. • The sediments slowly harden into rock and preserve the shape of the organisms.

  3. Fossils • Scientists who study fossils are • Fossils are usually found in rocks. • It is rare for the soft parts of an organism to become a fossil. Paleontologists. sedimentary

  4. Normally… Yummy stuff !! • when an organism dies, its soft parts often decay quickly or are eaten by other animals leaving behind the hard parts. • Only ones that get buried quickly by sediment stand a chance of getting preserved as fossils. Ex: bones, shells, teeth or seeds Look on page 241

  5. How Fossils form • http://www.bbc.co.uk/sn/prehistoric_life/dinosaurs/burying_bodies/burial/burial.swf

  6. Types of fossils: • Molds and Casts are the most common fossils found. • A mold is a hollow area in sediment in the shape of an organism or part of an organism. • A cast is a copy of the shape of the organism – the mold gets filled in.

  7. Types of Fossils • Petrified Fossils: fossils in which minerals replace all or part of the organism. It means “turned into stone”. • When the object is buried by sediment, water rich in minerals seeps into the cells. After the water evaporates, hardened minerals are left behind. Ex. Petrified wood and shark’s tooth

  8. Types of Fossils • Trace Fossils provide evidence of the activities of ancient organisms. Many are molds and casts. Scientists can discover an animal’s size and behavior from these. • Examples are: • footprints, animal trails, dung or animal burrows.

  9. Types of Fossils • Preserved Remains are formed when an organism is preserved with little or no change. • Many organisms become preserved in tar, amber (tree sap), and ice.

  10. Preserved in Amber • Hardened tree sap. • Delicate structures preserved (legs, antennae) • DNA has been extracted from these fossils…

  11. Preserved in tar • Tar pits are pools of gooey asphalt that are created when crude oil seeps up from deep inside the Earth through a crack (called a fissure). The less dense elements of the crude oil evaporate, leaving a deep, conical deposit of asphalt (a very sticky mess). Water pools atop the tar, attracting thirsty animals. As animals get stuck in the tar, predators are attracted to the trapped animals, and then they get stuck in the asphalt too.

  12. What types of fossils are these? These are molds and casts of a trace fossil.

  13. Keep guessing: Petrified claw fossil mold

  14. Last Examples: A preserved fossil of an ammonite.

  15. Why Study Fossils? • Scientists study fossils to learn what past life forms were like. • Paleontologists classify organisms in the order in which they lived. • All the information scientists have gathered is called thefossil record.

  16. Fossil Record • The fossil record provides evidence about the history of life and past environments on Earth. • The fossil record also shows how different groups of organisms have changed over time. Read page 244-5

  17. Changes in Earth’s History • The fossil record is often interpreted as showing catastrophic events in the past. This idea is called catastrophism. • Climate change, asteroid impacts, volcanic explosions

  18. Pre-Geico?

  19. Finding the Age of Rocks Through Rock Dating Ch. 8 section 2

  20. Ages of Rocks • These sedimentary rocks are stratified. In other words, each layer represents a different time period or age of rock.

  21. Ages of Rocks • The relative age of a rock is its age compared to other rocks. Use words like: “older or younger”. • The absolute age of a rock is its number of years since the rock was formed. Scientists can’t always know the exact date, but can usually get it within a couple of years.

  22. Can you guess what period of time these pictures come from? • When you look at pictures that are not familiar to you, you look for clues to tell you about it. • Types of Clothing and styles (hair, glasses) • Electricity? • If it is a real photo, is it black and white or color?

  23. Can you give an absolute date or only guess to this picture?

  24. First Clue: Position of Layers Youngsters • It can be difficult to determine a rocks absolute age. So… scientists use the law of superposition. • According to the law ofsuperposition, in horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it. Old timers

  25. Other Clues to Relative Age • Clues From Igneous Rock • Lava that cools at the surface is called an extrusion. Rock below an extrusion is alwaysolder. • Magma that cools beneath the surface is called an intrusion. An intrusion is always younger than the rock layers around and beneath it.

  26. Extrusive rocks are always older than the rocks below it.Intrusive rocks are always younger than the rocks it goes through. Lava formed on top of the rock These layers of rock were here before the magma intruded.

  27. Other Clues to Relative Age Rock had to be there first before it couldbreak andfault! • Faults (a break in the rock) are always younger than the rock it cuts through!

  28. Other Clues to Relative Age • Unconformities: An unconformity is a gap in the geological record that can occur when erosion wears away rock layers and other rock layers form on top of the eroded surface. New deposits Older layers

  29. Using Fossils to Date Rocks! • Scientists use index fossils to match rock layers. • An index fossil must be widely distributed and represent a type of organism that existed only briefly. • They are useful because they tell the relative agesof the rock layers they are found in.

  30. The Trilobite • One example of an index fossil is a trilobite. • Trilobites were a group of hard-shelled animals whose bodies had three distinct parts. • Scientists know when they lived and when they became extinct. • IF they find these in a rock layer, they use these index fossils to match rock layers.

  31. To Qualify as an Index Fossil: • Must be widespread. • Must be distinctive. • Must have a “short” life span. • Must be numerous! Echioceras: Jurassic Period

  32. The Geologic Time Scale • Geologists classify rock layers by their absolute age. • This summary is called the Geologic Time Scale. • Some dates are derived from fossils; some from radioactive dating methods.

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