The fossil record 10G

The Fossil Record

Fossils and Ancient Life

  • Fossils provide vital information of extinct species that have died out.

Types of Fossils

  • Fossils can vary widely in size and preservation.

    • Large Fossils: Entire preserved animals.

    • Tiny Fossils: Bacteria.

    • Trace Fossils: Includes casts of footprints, burrows, tracks, or droppings.

Fossils in Sedimentary Rock

  • Most fossils are preserved in sedimentary rock.

Evaluating Evidence in the Fossil Record

  • Fossils reveal information about:

    • Structures of ancient organisms.

    • Sequential nature of groups in the fossil record.

    • Evolution from common ancestors.

    • Ecology of ancient environments.

Dating Earth's History

  • Relative Dating:

    • Places rock layers and fossils in a time sequence.

    • Determines whether a fossil is older or younger than others.

    • Uses index fossils to establish and compare the relative age.

  • Radiometric Dating:

    • Relies on radioactive isotopes that decay at a steady rate.

    • Half-life: time required for half of the original radioactive atoms to decay.

    • Calculates age using proportions of radioactive to stable isotopes.

Geologic Time Scale

  • Timeline of Earth's history based on relative and absolute dating.

  • Main divisions include eons, eras, and periods.

Establishing the Time Scale

  • Early paleontologists used rock layers and index fossils to establish relative age.

Division of the Geologic Time Scale

  • Eons Recognized:

    1. Hadean Eon: First rocks formed, about 4 billion years ago.

    2. Archaean Eon: Life first appeared.

    3. Proterozoic Eon: Stable continents formed; evolution of eukaryotic cells.

    4. Phanerozoic Eon: From the end of the Proterozoic to present.

  • Eras of the Phanerozoic Eon:

    • Divided into Paleozoic, Mesozoic, and Cenozoic eras.

    • Eras subdivided into periods ranging from nearly 100 million years to just under 2 million years.

Effects on Life

  • Global climate change, mountain building, islands emergence, continental drift, changes in ocean and continental levels, and meteor impacts have altered Earth’s habitats.

Biological Forces

  • Actions of living organisms have changed atmospheric, oceanic, and terrestrial conditions over time.