TOP IMAGE IS FOLDING, BOTTOM IMAGE IS FAULTING)
- Index Fossil - short-lived, geographically widespread occurrence.
MEASURING ABSOLUTE TIME NOTES:
- Tree Rings - Each ring represents a single year (single/fall) the width of the ring depends upon temperature & rainfall (TOP PICTURE),
- Varves - Glacial lake deposits, a thick light-colored layer in the summer and a thin dark layer in the winter (BOTTOM PICTURE).
RADIO ACTIVE NOTES:
- Radioactive Dating: Used to date back in time, certain rocks contain radioactive isotopes.
- Radioactive Isotopes: Atoms of elements that give off radiation from their nuclei.
- Radioactive Decay: The process by which a radioactive isotope changes into a new stable element.
- Radiocarbon Dating: Uses the Radioactive Isotope Carbon-14 found in all living things. Because carbon-14 is continually absorbed by food & water it stays constant in living things. When the living thing dies the % of Of carbon-14 decreases at the rate of its half-life (can be used to date back 100, 000 years).
PRE-CAMBRIAN TIME NOTES:
- Precambrian time is all of the geologic time before the Paleozoic Era, Precambrian rocks lack fossils because most of the organisms were microscopic bacteria and algae, Stromatolites are algal reefs that make up a large part of the fossils from the Precambrian, ½ Of the world’s metallic minerals are found in Precambrian rocks.
- The Paleozoic era marks the beginning of an abundant fossil record. North America was over the equator and our climate was warm with few seasonal changes.
- Cambrian Period - Trilobites & Brachiopods are the most common fossil. Trilobites are found throughout the Paleozoic era but never more abundant & widespread than the Cambrian (index fossil).
- Devonian Period - “Age of the Fishes” fishes were jawless & were covered with heavy plates.
- Ordovician - All life still in the oceans.