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- the method used by geologists to match rock layers of the same age.
- Matching is based on similarities in the sequencing of layers or unique common fossil species or groups of fossils.
what are responsible for plate techtonics
currents near the bottom of the sea are.... (faster/slower)
Age of earth
4.6 billion yr old
how many mi in bi
Any evidence of past life, ice age, or older.
actual remains, may or may not be changed
usually bones, teeth, or shells, rarely is it soft fleshy parts of the organism
tracks, traits, burrows (called trace fossils)
coprolite ( fossil dung )
Conditions Favoring preservation of fossils:
presence of hard parts (bone, teeth, shell)
Common Types of Preservation
original materials are broken down and is replaced by minerals from groundwater occurs at a molecular level.
original bone/shell is turned to stone.
The original material is dissolved away by ground water and minerals from the surrounding rock take its place.
Common replacement minerals: quartz, calcite, rarely hematite.
- all volatile (blood, fat, etc,..) (REACTIVE)
- all volatile ( reactive substances, liquids) are squeezed out leaving a thin film of carbon. Commonly preserves plants, fish, rarely others (salamanders, Jellyfish)
-all fluids (water based, also fats, blood) are squeezed out leaving a thin film of carbon. Commonly preserves leaves, fish, rarely frogs, salamanders, jellyfish.
thin bodied organisms with chitonous (scales,exterior) exoskeletons
- a three-dimensional replica of the organism (usually bone/shell)
- may be internal (from the inside of a shell, hardened mud) or external
surrounds the clasts (like a cake mold)
Rare Types of Preservation
- - amber: fossilized tree sap
- - ice: only Ice Age organisms
- - tar: whole community preserved
the age of a fossil rock layer or igneous rock (intrusion/lava flow) in yrs.
...break down at a known rate into stable elements (daughter elements) called half lifes
the amount of time it takes for 50% of a radioactive element to break down into a stable element (daughter element)
any layer cut by a fault or intrusions older than the fault or intrusion
gap in the rock record stripped away by erosion
Geologic time is broken up into (equal/unequal) units of time based on....
......major events and/or major changes in life forms units from largest to smallest
Eon -> Era -> Period -> Epoch
oldest rocks on Earth
Photosyntheis = first life
first single celled organisms
570 mya- now
- visible life
- simple multicellular fossils
Proterozoic Eon- origin of Earth
4.6 -2.5 bya?
570 mya- now
- "ancient life"
- Age of Invertabrates
- "Middle Life"
- Age of Reptiles
- Dinos are dominant
- Recent Life
- age of mammals
66.4 mya- now
order of time
- Precambrian Time: Origin of Earth
- Proterozoic Eon
- Phanerozoic Eon: Paleozoic Era
- Mesozoic Era
- Cenozoic Era
used for determining the age of rock layers
****must be common widespread geography exist for a limited time period****