Transcript Lecture 4: Geological Time

Lecture 4:
Marine Fossils, geologic
time scale
Corresponding Reading Material
~ Lab Manuel: Marine Fossils
~ Levinton:chapters 2 and 3
Evidence for Evolution
 Similar life forms that are related
 Vestigial traits and homologous characters
 Evidence from the fossil record
~fossils are any trace of an organism that lived
in the past.
 Fact of extinction
 Environmental change
 Plate tectonics
Geological Time
 Scientists have
divided time since
the formation of
the Earth into a
geological time
scale.
 Each period has
characteristics or
events that are
unique to them.
How do we know the age
of the Earth??
 During Darwin’s time, the Earth was
thought to be 6,000 years old. Why??
 Moon rocks and meteorites
 Theory of uniformitarianism states that
geological process that are occurring
today were the same in the past.
Relative vs Absolute Dating
 Relative Dating = refers to the determination of the
age of a rock or geological sample by comparing its
position to the position of other samples.
 Absolute Dating = refers to the determination of the
age of a geological sample by calculations or
radiometric decay and/or its position in relation to other
samples
Dating Techniques
 Radiometric Dating = the process of
determining the age of rocks by observing
the ratio of unstable radioactive elements to
stable decay products
~ Half-life = is the time it takes for one
half of all the unstable nuclei in a sample to
decay. During this process the radioactive
element becomes a new element.
Dating Techniques
 Paleomagnetism = is the remnant magnetic field of a rock
~Tiny particles of iron-bearing minerals are present in
balsamic rocks
~ These particles align with the Earth's magnetic field at the
time they are formed and freeze in place as the rock
solidifies
~ In the last 26 mill yrs, the
poles have reversed 48 times.
~ This techniques is used to
calibrate the geological time
scale and to reconstruct
continents
Dating Technique
Dating Technique
How Are Fossils Made?
 There are five ways an organism can become fossilized:
Trilobite Fossil
1. Permineralization (Petrification) = this process involves
the replacement of the original organic tissues w/ minerals
from the surrounding rock, including silica, calcite, or pyrite
2. Unaltered Preservation = occurs when the organism is
preserved in its original state and is protected from the affects
of permineralization (Ex: Insects which become trapped in tree
sap which turns into amber)
3. Carbonization (Coalification) = results form the removal
of all but the carbon elements (other elements such as
hydrogen, oxygen, and nitrogen are removed)
How Are Fossils Made?
4. Authigenic Preservation = these fossils are mold and casts or
organisms which have dissolved or rotted away, leaving only a
trace of their existence (the parts of the organism that are replaced
are usually the hard parts of the dead organism)
5. Recrystalization = occurs when crystals form within the original
structure, eventually replacing it and resulting in a crystallized copy
Horn Coral Fossil
Brachiopod Fossil
Pictures of Fossils
Sponge Fossil
Eocene Fish Fossil
Ammonite Fossil (Jurassic Period)
Tuzoia Fossil
Fossils Over Time

Below the chart shows when different organisms appear within
the fossil record.
Burgess Shale Fossil
 The Burgess Shale is is an
exceptional Middle Cambrian
age (~540 mya) fossil locality
located in Yoho National Park
in the Rocky Mountains near
Field, British Columbia,
Canada.
 It is special because of the
soft-bodied preservation of a
wide variety of fossil
invertebrate animals.