Fossils

• Fossils


  Remains and traces of ancient plants and animals
• Fossilization

  1. Organism dies

  2. Remains buried in sediment

  3. Chemical transformations replace organic compounds
• Geologists look for clues in sedimentary rock layers (strata) to map out what happened on Earth billions of years ago
• Fossil record


  Remains of organisms that have been preserved in rock layers
• Law of Superposition


  In a sequence of undisturbed sedimentary rocks, the layers on the bottom were deposited first and are therefore older than the layers on top
• Law of Cross-cutting Relationships


  When two geologic features cross or intersect, the feature that cuts through the other is younger
• Index fossils


  Fossils of organisms that existed for a relatively short period and were widespread geographically
• Geologic Time Scale


  A framework that organizes Earth's history into distinct intervals based on significant events and changes, with fossils playing a crucial role in establishing
• Divisions of Geologic Time Scale

  • Eons
  • Eras
  • Periods
  • Epochs
  • Ages
• Fossilization involves the molecule-by-molecule replacement of organic matter by inorganic compounds, creating an exact replica of the original
• Molds form when hard parts of an organism are buried in sediment and then dissolve over time, leaving a hollow area in the shape of the organism
• Casts form as a result of the mold, with water and dissolved minerals filling the empty space and leaving mineral sediments behind
• Ichnofossils or trace fossils are marks left by an animal or plant, such as nests, burrows, or footprints
• Carbon fossils are formed when an organism dies and is buried in sediment, with only the carbon remaining after the other materials break down