Lab Assignment_ Fossils
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University of California, Los Angeles *
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Course
70B
Subject
Geology
Date
Feb 20, 2024
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3
Uploaded by BrigadierStork4059
CLUSTER 70B: Evolution of the Cosmos and Life
Name:______________________
WEEK 5 LABORATORY/DISCUSSION WORKSHEET
INTERPRETING FOSSILS
LAB ASSIGNMENT
I. Manganese dendrite
The first specimen in today’s lab is no fossil but instead is a pseudo-fossil. This looks
somewhat like a fossil and it misleads many people. This particular kind of pseudo-fossil is
known as a manganese dendrite and is frequently confused with fossil ferns. Dendrites are
formed by solutions penetrating along fractures called joints in hard rocks. The joints are caused
by shrinkage during cooling (igneous rocks) or dewatering (sedimentary rocks). The black color
of this dendrite is due to manganese oxides. The yellowish and reddish colors are due to iron
oxide (rust). The dendrite has fractal properties and serves as a model for the flow of fluids
underground. Keep in mind that flat fossils (such as ferns) in sedimentary rocks are preserved in
between layers of sediments. Look closely at the pattern in this rock and compare with the fern
fossil next to the dendrite sample.
List two lines of evidence suggesting this is not a plant
fossil.
II. Trackways
The fossil in this station consists of traces left by organisms in the sediments that later were
preserved when sediments filled them up.
List three basic characteristics of the animals that
made these traces.
Hint: think very basic!
Why are trackways given their own genus name, even though they are not true genera and
were made by organisms that possibly already have names?
III. Plant fossils
These fossils show imprints of plants. The smaller one also has a thin stain.
Is any of the
original plant material still present in these fossils? Why do you think so? (3 points).
Given the stain on the smaller specimen, what can you say about the environment in which
this plant was preserved?
IV. Sediment mold of a snail
In this specimen, only the sediment that filled in the snail shell is preserved. Compare
with a snail shell to visualize what this specimen represents.
Briefly outline how this fossil
formed.
V.
Permineralized wood
Dead wood is a highly porous material composed of tough cell walls that once housed living
cells. The space occupied by the cells is often filled by mineral cements such as quartz. The logs
of the “Petrified forest” in Arizona are preserved in this way. Silicification occurs early in the
fossilization sequence and so this log has been able to resist compression by the weight of the
overlying sediment. Note how the radial structure of the wood and the growth lines are preserved
by this permineralization.
How would you be able to determine information about past
climates by looking at permineralized or petrified wood?
VI. Coprolites
Coprolites are fossilized feces. Although it is typically impossible to determine exactly which
species was responsible for a given coprolite, in a few cases this can be done with reasonable
certainty.
How would you try to determine what the individual that made this coprolite was
eating? What kind of things could you identify in a coprolite?
VII.
Banded Iron Formation
This station shows a part of a 2.5 billion-year-old banded iron formation. Banded iron
formations are composed of oxidized iron minerals. The red and black bands in this specimen are
made of oxidized iron minerals, the red iron oxide hematite (Fe
2
O
3
) and the black magnetic iron
oxide, magnetite (Fe
3
O
4
).
What does the presence of banded iron formations in rocks 2.5 to 2
billion years old tell us about the environment then? Why are banded iron formations
commonly called “oxygen sinks”? Why have no new banded iron formations formed over
the last 2 billion years?
Hint: What turns iron red? Knowing what you do about rocks being
formed in layers over time, what might have happened to make the different colors (black and
red) and why?
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