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Cosmic Calendar

Cosmic Calendar. Reading Rock Records. Telling Time. Relative Time – places events in a sequence but does not identify their actual date of occurrence. Absolute Time – identifies the actual date of an event. Laws .

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Cosmic Calendar

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  1. Cosmic Calendar

  2. Reading Rock Records

  3. Telling Time • Relative Time – places events in a sequence but does not identify their actual date of occurrence. • Absolute Time – identifies the actual date of an event

  4. Laws • Law of superposition - states that in a sequence of undisturbed sedimentary rock, the oldest rocks are on the bottom, while the youngest is on the top. • Law of cross-cutting – states that an igneous rock is younger than the rock that it has intruded, or cut across • Law of included fragments – states that pieces of one rock found in another rock must be older than the rock in which they are found. • Unconformity – is a place in the rock record where layers of rock are missing.

  5. Geologic Timetable • EON – the longest segment of time • Eras – the segment of time EONS are divided into • Periods – era are divided into these • Epochs – period are divided into these

  6. Fossils Records

  7. How are they formed? • Fossils – any evidence of earlier life preserved in a rock. • Original remains • The actual, unchanged remains – of the plant or animal are preserved. • Replaced remains • The soft parts of the animal are no longer there, but the hard parts are still visible • Molds and Casts • Mold is where you have left a hollow depression in the rock • Cast is where you have a new mineral fill a mold • Trace Fossils • Evidence of life other than the remains of a plant or animal

  8. Original remains

  9. Original Remains

  10. Replaced remains

  11. Cast and Mold

  12. Index Fossils • Fossils that are used to determine ages of rock that they come from • Also known as guide fossils

  13. Measuring Absolute Time

  14. Tree Rings

  15. Varves

  16. Decaying • Radioactive Decay • When an element loses mass as it ages • Half life • The rate at which that process happens • Radiocarbon dating • An isotope that measure the amount of carbon decay

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