Download Fossil and Relative Age of Rock notes

Fossil and Relative Age of Rock notes
paleontologists - Scientists who study fossils
The Fossil Record :The record of fossils on earth that help give evidence about the history of life on earth. Shows how
groups of organisms may have changed over time
– This is much of what the Theory of Evolution is based on; a gradual change in living things over long
periods of time
Fossils are NOT bone: When a fossil is found in rock – it is not the actual organism – the organism has been replaced
with minerals
Types of Fossils
Made of Minerals: Petrified fossils, Mold, Cast, Carbon film, Trace fossils, Index fossils
Organism: Preserved remains
 Mold is the hollow area the organism once took up, usually concave (Ex: ice cube tray)
 Cast is the copy of the shape of an organism that would be made in a mold, usually convex (Ex: ice cubes)
 Preserved Remains: Jackpot! Organisms can become preserved whole when they are caught in tar, amber (tree
sap), mud pits, or ice that hardens around them. Usually small organisms or plants.
 Petrified Fossils: Mineral replacement; As organism decomposes and erodes away minerals flow in to replace
pieces of organism (Ex: Petrified wood)
 Carbon Film: Thin “film” coating of carbon is left on the rock when the organism gets squished – only carbon
film is left behind
 Trace Fossils: Evidence (or traces) of an organisms activity or life (Ex: footprints, burrows, termites eating, etc)
 Index Fossils: Fossils of the same short lived species that are widely distributed over the earth
– Help geologists match rock layers that have moved
– Show relative age of rock they are found in
a.
a. Mold
B.
B. Cast
C.
D.
C. Preserved Remains D. Petrified
E.
E. Carbon Film
F.
G.
F. Trace Fossils G. Index Fossils
Relative and absolute age of rocks
 The relative age of a rock is its age compared to the ages of other rocks, it is like comparing your age to
someone else’s. The relative age does not provide its absolute age
 The absolute age of a rock is the number of years since the rock formed; It is difficult for geologists to determine
the absolute age
 The law of superposition states that in horizontal layers of sedimentary rock, each layer is older than the layer
above it and younger than the one below it.
 Unconformity is where an old eroded surface is in contact with a new rock layer.
 Faults can occur only after rock layer have formed; therefore rock layers are older than the faults
 Igneous rocks that have formed as magma and cool underground are called intrusions
 Extrusions are volcanic, molten materials that cool and harden when they reach the Earth’s surface
Law of superposition
Unconformity
Intrusion (#4)