PA STANDARDS
3.2 Inquiry and Design
3.2.7
B. Apply process knowledge to make and interpret observations.
 Describe relationships by making inferences and predictions.
C. Identify and use the elements of scientific inquiry to solve problems.
 Generate questions about objects, organisms and/or events that can be answered through scientific investigations.
3.3 Biological Sciences
3.3.7
D. Explain basic concepts of natural selection.
 Describe the role that fossils play in studying the past.
 Explain how biologic extinction is a natural process.
3.5 Earth Sciences
3.5.7
A. Describe earth features and processes.
 Describe major layers of the earth.
 Describe the processes involved in the creation of geologic features (e.g., folding, faulting, volcanism,
sedimentation) and processes that are seen today (e.g., erosion, weathering, crustal plate movement) are similar to
those of the past.
 Identify living plants and animals that are similar to fossil forms.
THE SCROLL OF TIME
About 200 years ago geologists realized that the earth was very old. As they added up the thickness
of rock strata found over the earth, they concluded that it would take millions of years for natural
processes to lay down the many thousands of feet of sediments that later solidified into rock. Their
estimates of the earth's age grew longer and longer, but these were mostly guesses.
Physicists came to the rescue by providing a radiometric scale of time. Radioactive chemical
elements decay into other elements at a fixed rate. By measuring the amount of decay of certain
forms (isotopes) of Uranium, Thorium, Potassium, and other elements, it became clear that the earth
was 4.5 or 4.6 billion years old. Earlier, geologists had divided up the rock strata of the earth into a
geologic time scale, using fossils and major events of upheaval and mountain formation. The
radiometric scale made it possible to compute the length of the units of geologic time. The last 550
million years of the geological time scale are shown in Figure 1.
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Although there are traces of life – of bacteria and primitive algae- dating to about 3.7 billion years
ago, evidences of life during that long stretch of time are scarce. The Paleozoic Era, lasting from
about 550 mya (million years ago) to about 250 mya, is the first era of abundant life on earth.
Time divisions within an era are called periods. The periods of the Paleozoic Era, starting with the
earliest are:
Cambrian Period
Ordovician Period
Silurian Period
Devonian Period
Mississippian Period
Pennsylvanian Period (guess where they got this name!)
Permian Period
During the first half of the Paleozoic Era most life consisted of fish and invertebrate animals in the
sea. During the second half, plants, insects, amphibians, and reptiles colonized the land. The great
coal seams of Pennsylvania originated in steamy forested swamps of the Pennsylvanian Period.
If you are asked by your teacher to learn the periods, you can use the memory aid Can Old Sailors
Digest My Pickled Peppers?
Many animals, such as the trilobites, and plants became extinct at the end of the Paleozoic Era. The
next era, the Mesozoic Era lasted from about 250 mya till 65 mya. This was the age of
dinosaurs. Primitive mammals and birds also lived during the Mesozoic.
There are three periods of the Mesozoic Era:
Triassic Period
Jurassic Period (think of the movie Jurassic Park).
Cretaceous Period
Tom's Jumping Cat
Many life forms, including the dinosaurs and ammonites became extinct at the end of the Mesozoic
Era. The impact of a giant meteorite or comet probably caused, or helped to cause, the extinctions.
We are now living in the Cenozoic Era, a short era beginning 65 mya. This is the era of
flowering plants, grasses, and mammals. Giant cave bears, saber-tooth tigers, mastodons, and other
great mammals only went extinct recently. There are two periods of the Cenozoic:
The Tertiary Period. This period spans about 63 my from the extinction of the dinosaurs to the
beginning of the ice ages.
The Quaternary Period consists of the last two million years. This is the time of the ice ages.
Our own species, Homo sapiens, appeared during the late Quaternary.
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VOCABULARY.
Fossil. The remains of organisms that once lived on the earth.
Geological Time Scale. The time divisions of the history of the earth, beginning with the
origin of the earth 4.6 billion years ago.
Era. A major division in the geological time scale. There have been three eras since life on
Earth became abundant: the Paleozoic Era, Mesozoic Era, Cenozoic Era. We live today in the
Cenozoic Era.
Period. A smaller division in the geological time scale. Each era is divided into several periods,
most of which lasted 50 million years or so.
Radiometric dating. A precise dating of rocks of the earth based on the slow decay of
radioactive isotopes in those rocks.
Phylum. A major grouping of organisms all with a similar body plan. There are thirty-some
phyla of animals, such as, Arthropoda, Chordata (our phylum), Mollusca, etc.
Genus. A much smaller grouping of closely-related species. Examples: genus Rattus, all species
of rats, genus Quercus, all species of oak trees, etc.
FOSSILS
Fossils are the remains of organisms that once lived on the earth. Most fossils are altered
remains of animals or plants entombed in rocks, sediment, or even ice. Other fossils are tracks or
footprints or even petrified dung left behind by animals. The most common way that fossils
form is for organisms to be buried quickly in sediment. The soft parts usually rot away, leaving
the hard parts – bones, teeth, shells, etc. to fossilize.
During fossilization, the hard parts gradually dissolve and are replaced by minerals. As the
surrounding sediment hardens into rock, the mineral replacement of the original fossil also
hardens. The mineral replacement may be identical to the surrounding rock, or may be pyrite
(fools gold), calcite, pure silica, or other minerals.
Fossils can also form in other ways. Insects can be directly preserved in amber and wooly
mammoths preserved in Siberian glacial ice. Soft-bodied organisms such as jellyfish, worms,
and ferns can be compressed to thin, flat layers of carbon that still reveal the shape of the
organism in two dimensions. Seashells may entirely dissolve away in rock, leaving behind
impressions of their shapes as empty molds in the rock.
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INDEX FOSSILS
Fossils are widely used to study the evolutionary history of life. They are also used to
date the ages of rock strata from different places. Most species of animals and plants are
extinct. Take the example of the trilobite Olenellus. This animal only lived in the
Cambrian Period and then died out. So if a geologist finds a fossil of the trilobite
Olenellus anywhere in the world, he or she knows the rocks there are of Cambrian age.
Such fossils found only in rocks of certain ages are called index fossils. Geologists know
of thousands of index fossils and use them to determine the ages of rock strata in many
places. If geologists find oil in a particular rock formation, they will look for index
fossils for that formation in other places in hopes of finding oil there too.
Olenellus
Fossils on Display
(1)
Large limestone slabs of early Paleozoic age from central PA covered with fossil
corals, brachiopod shellfish, and other organisms.
(2) Tray of small invertebrate and vertebrate fossils found over the world.
(3) Tray of large plastic replica fossils. These have been painted
by college students to resemble their original colors. Please
handle them carefully to avoid chipping paint.
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Fossil Lab Exercises and Worksheet
I. Exercise I. is to identify the 20 replica fossils in the plastic tray.
Take each fossil out of the tray and look at it carefully. Now compare the fossil to the pictures of
fossils in Figure 2. Your fossil will be identical to one of the pictures. When you identify a
fossil, you will know its genus (plural is genera) (such as Pecten, Neospirifer, Flexicalymene,
etc.) and the geological period in which it lived.
Note that three fossils are of teeth, not whole animals: Equus (horse), Merychippus (primitive
horse), and Carcharodon {shark} teeth.
Here are some hints to help in identification. The two bivalves (clams) Pecten and Venericardia
are reddish or yellowish in color. The sea urchin Tetragramma is reddish also.
Of the three coiled ammonite shells (related to present-day squid), Meekoceras is large and light
gray-tan in color, Acanthoscaphites is smaller, is knobby, and is blackish, and Muensteroceras
is small, smooth, and blackish in color. Michelinoceras is a relative of the ammonites, but has a
straight, gray shell.
There are 5 brachiopods (ancient kind of shellfish). Olenothyris is large, egg-shaped, and
grayish in color, Eospirifer is medium-size, fat, and light grayish-tan. The three spirifers are
dark gray: Mucrospirifer is the widest, Spirifer is smallest, Neospirifer is in-between in size.
There are two trilobites (ancient extinct arthropods). Both are rolled up to protect their
undersides, the way pillbugs and sowbugs do today. Phacops is larger and is brown,
Flexicalymene is smaller and light gray.
Refer to Figure 2 to identify the teeth and the other fossil replicas..
Lay out the fossils on the table and label them on strips of file card. Group them from left to
right according to age, Ordovician fossils on the far left, Quaternary fossils on the far right.
Your teacher will check your identifications for accuracy.
II. Exercise II is to group the fossils according to phylum.
All living and extinct animals belong to thirty-some different phyla. Members of each phylum
have a distinct body plan. Examples: all members of the phylum Mollusca have one or two
external shells and a muscular foot; almost all members of the phylum Chordata have an
internal backbone, etc.
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Figure 3 shows typical fossil and living animals of five phyla. All of your fossils belong to
these five phyla. Using Figure 3 as a reference, sort each fossil into the phylum to which it
belongs. Note: most of the fossils in this figure do not belong to the same genera as your
replicas.fossils.
After the teacher has checked your fossil layout by name and age in Exercise I., display
The same twenty fossils by phylum. Lay them out from left to right in this order:
Brachiopoda, Arthropoda, Mollusca, Echinodermata, Chordata. Label each phylum on a
strip of file card.
III. Exercise III uses index fossils to discover the age and
arrangement of rock formations.
This information helps geologists to find coal, oil, and other natural resources, ground water
zones, and areas where earthquakes occur.
A. The geological cross-section of Figure 4 shows a fracture zone running from the surface
deep into the earth. A geological fault has broken up the rocks in the fracture zone and has
uplifted the rocks on one side.. Earthquakes often occur along such faults.
The uplifted side of a fault brings older rocks closer to the surface. Erosion may expose the
older rocks at the surface on the uplift side. Younger rocks will remain at the surface on the side
not uplifted. Use the index fossils in Figure 4 A. to determine the age of the three rock
formations on both sides of the fault.
1.On Figure 3 label the ages (periods) of the three rock formations on the left side of the
fault.
2. On Figure 3 label the ages of the three rock formations on the right side of the fault.
.
3. Which side of the fault is uplifted? Explain your answer.
B. On the left side of Figure 4B. an oil well has been drilled into a pocket of oil in a rock
formation. The right side of the figure is 100 kilometers away. Use index fossils to determine
the ages (periods) of the rock strata.
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1. With this knowledge, draw an oil well on the right side of Figure 3B and draw a drill
shaft into the same formation in which oil was discovered at the first well.
.
Explain your reasoning in drilling to that rock formation.
IV. Exercise IV is a way of visualizing the geological time scale.
Each team will tape together two sheets of graph paper, the long way vertical, so that the vertical
length is 22 inches. Use the wooden rulers provided in the kit. With a pencil or pen draw a
vertical bar in the center of the sheets. The height of the bar should be 50 cm and the width 5
cm. The 50 cm height represents the geological time scale from the beginning of the Paleozoic
Era to the present time, a total of 542 my.
How do you represent 542 my on a 50cm scale? You divide 542 by 50, or 542/50 = 0.092.
That means each one million years is 0.092 cm (just under one mm) on the scale.
.
Now mark off the lengths of the Paleozoic, Mesozoic, and Cenozoic Eras, starting at the bottom..
Length of Paleozoic Era = 291 my. 291 x 0.092 = 26.77 cm. On the bar, draw a horizontal line
26.77 cm above the bottom of the scale to indicate the length of the Paleozoic Era.
Mesozic Era = 186 my
Cenozoic Era = 65 my
Figure out the lengths of these eras and draw horizontal dividing lines across the time scale bar.
Now that the eras are measured off, determine the lengths of all the periods, and mark them off,
starting with the Cambrian Period at the bottom. Refer to Figure 1.
Cambrian = 54 my
Ordovician = 45 my
Silurian = 28 my
Devonian = 57 my
Mississippian = 31 my
Pennsylvanian = 33 my
Permian = 48 my
Triassic = 51 my
Jurassic = 54 my
Cretaceous = 80 my
Tertiary = 63 my
Quaternary = 2 my
The divisions of the geological time
scale are now complete.. The next step
is to color in the periods.
The United States Geological Survey
(USGS) uses standard colors to illustrate rock outcrops of different periods on its maps. Use the
same colors – or the closest you can – to the USGS system with the provided colored pencils.
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Cambrian = orange-red
Ordovician = pink
Silurian = light purple
Devonian = dark blue-purple
Mississippian = light blue-purple
Pennsylvanian = dark blue
Permian = light blue
Triassic = blue-gray
Jurassic = blue-green
Cretaceous = green
Tertiary = orange-brown
Quaternary = yellow
To finish the geological time scale, label all eras and periods.
Add these last features, below, to the geological time scale:
1. About 90% of all species of animals and plants became extinct at the end of the Permian
Period. The cause may have been an asteroid or comet impact, or perhaps widespread volcanic
activity.
Write the letters P.E. on your time scale at the end of the Permian Period.
2.. The dinosaurs, ammonites, and many other species became extinct at the end of the
Cretaceous Period, probably due to an asteroid or comet impact. Write the letters C. E.
on your time scale at the end of the Cretaceous.
3. Although mammals existed earlier, the true age of mammals starts at the dawn of the
Tertiary Period. Write A.M. on your time scale at the beginning of the Tertiary.
4. Great tropical forests existed during the Mississippian and Pennsylvanian Periods. The
remains of these forests were compacted into coal beds all over the world. Write T. F. on these
two periods on your time scale.
5. Trilobites lived from the Cambrian Period to the end of the Paleozoic Era, and then became
extinct. What extinction event happened at the end of the Paleozoic Era?
.
__________________________?
6. Our own species, Homo sapiens, originated fairly late in the shortest of the geological periods.
Write H. S. on the time scale at about the time Homo sapiens evolved.
Today's menu - Middle School students!
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