EARTH 7 Lecture Notes - Lecture 2: Metamorphic Rock, Fossil, Permineralization
10/3/17
●Igneous rocks - primary rock that forms directly from a melt
○ We can often determine their absolute ages
○ Only rarely preserve fossils
■ Exception to this is volcanic ash fossils (tiny droplets of solidified lava-tiny
glass fragments)
●Sedimentary rocks -formed by the deposition and subsequent cementation of that
material at the Earth's surface and within bodies of water.
○ almost all fossils are found in sedimentary rocks
○ As sediments become rock, these remains become fossils.
○ We can often determine the relative ages of these rocks.
○ Normally accumulates in low lying areas (deserts, lakes, beaches)
■ Carried by wind or water.
■ Carried out from inland by rivers.
● Sediments become smaller and smaller farther out they go.
● Metamorphic rock experiences such high heat that it changes rock but doesn’t melt.
●Fossil - any evidence of ancient life
○Body fossil - part of an organism (leaf is a body fossil of a tree)
○Trace fossil - evidence of an organism’s activity (nests, running tracks)
● How fossils form
○ 1. Death
○ 2. Decay
■Most remains never make into the fossil record due to various types of
decay
■ Trampled, eaten, destroyed
● Some sedimentary environments help reduce decay
○ Floods,
○ 3. Burial
■ Needs to happen before total decay
■ More sediment accumulation leads to deeper burial and the eventual
formation of rock layers.
○ 4. Lithification (rockification) & Fossilization
■ Mud + pressure = shale
■ Sand +pressure = sandstone
■ Gravel + pressure = conglomerate
● Fossilization
○ 1. Permineralization - minerals fill in empty pore spaces.
○ 2. Replacement - new minerals replace original stuff.
■ Most dinosaur fossils have undergone a
combination of permineralization and replacement.
Document Summary
Igneous rocks - primary rock that forms directly from a melt. We can often determine their absolute ages. Exception to this is volcanic ash fossils (tiny droplets of solidified lava-tiny glass fragments) Sedimentary rocks - formed by the deposition and subsequent cementation of that material at the earth"s surface and within bodies of water. Almost all fossils are found in sedimentary rocks. As sediments become rock, these remains become fossils. We can often determine the relative ages of these rocks. Normally accumulates in low lying areas (deserts, lakes, beaches) Sediments become smaller and smaller farther out they go. Metamorphic rock experiences such high heat that it changes rock but doesn"t melt. Fossil - any evidence of ancient life. Body fossil - part of an organism (leaf is a body fossil of a tree) Trace fossil - evidence of an organism"s activity (nests, running tracks) Most remains never make into the fossil record due to various types of.
