GEL 12 Lecture Notes - Lecture 3: Petrified Wood, Metasequoia, Permineralization
Fossils
1. What are fossils?
a. A part or all of the body of an organism of the past or its impression preserved in
whatever way
b. Sometimes the body is not preserved, shape is preserved as a mold
c. Trace fossils: recording somethings movements like footprints
2. Are living fossils fossils?
a. Living fossils were once thought to be extinct but it is not necessary to the definition
b. Examples: nautilus, horseshoe crab, metasequoia, coelacanth
c. Living fossils: group of organisms that have not changed their general shapes since they
were last seen in fossil record
i. they are not fossils because they are still living today
3. How are typical fossils made?
a. Water leaves the carcass, decreases the volume (especially vertically)
i. Loss of water
ii. Exchange of chemical ingredients with surrounding water (mineralization)
b. Permineralization
i. Petrified wood cross section, made it very tough
ii. Water brought in silicates into tissues
c. Dissolution/replacement
i. Dinosaur bone cross sections
ii. Water dissolves existing bone minerals: calcium phosphate
iii. Calcium used to make calcium carbonate: very common
d. Carbonization
i. Everything dissolves except for carbon, preserves shape
4. Would the fox that I saw the other day become a fossil in the future?
a. Unlikely, carcass has to survive many obstacles
i. Consumption by other organisms (bone eating bacteria)
b. Breakage, disarticulation
c. Metamorphism, recrystallization: loss of shape (when buried in rock in water)
d. Erosion: lost forever
e. Need to be discovered, if actually fossilized, need to be showing on surface
f. Organisms are rarely preserved and found as fossils
5. How complete is the fossil record?
a. 600 million years, only discovered 1/5 of the species, around 1.6/8
b. How many species turnovers? (origination/extinction)
i. Species longevity: very difficult to figure out
c. There must have been millions and millions of species but it is difficult to set a number
d. If 99% species are extinct, then there have been 500 million species
i. But this is a very poor estimation
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