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Vertebrate Fossils in Geologic Time

© 2008 Barbara J. Shaw Ph.D., Science A to Z

Permission is granted to make and distribute copies of this lesson plan for educational use only.

Background material:

Materials:

Classroom

butcher paper – 15 feet strip rulers

markers glue sticks

yardsticks drawings of vertebrate fossils

Students

copy of vertebrate fossils glue sticks

paper timeline scissors

optional: color pencils/markers

Background:

The Earth is old. Scientists use a variety of techniques to determine when the solar system, and the Earth formed. Radiometric dating is one method. The problem on Earth, though, is our planet is dynamic. The rock cycle eventually leads to rock being melted, and all history is erased. We haven't found any rock that is 4.6 billion years old (4.03 billion years is the oldest found so far), although scientists do accept the Earth to be that old. This estimate is based on meteorites. They formed about the same time as the Earth. Since meteorites don't get melted, they preserve the molecules that can be dated.

Stratigraphy is the study of rock layers and their relative ages. In geology, the Law of Superposition suggests that rocks in the deepest layers are older than the rocks near the surface. Therefore rock layers can be thought of as pages in a history book that was written backwards with the most current events in the front and the most ancient history in the back. However, various geologic forces can disrupt rock sequence chronology, including erosion, folding and faulting. In these processes, entire layers might erode away, fold on top of earlier rock, or ripple.

One of the main reasons geologists study fossils is to help them sort out all the confusion that can occur in studying rock sequences. Long before radioactive dating was used to tell ages, geologists were using fossils to age rock layers.

In the last 3 billion years, billions of different species have come and gone - far too many for one person to know them all. This is why some paleontologists specialize on the plants and animals of a particular time period, while others study a single type of plant or animal and how it evolved and/or went extinct over several time periods. What makes fossils so useful to aging rock is that an individual species seldom lasts more than 2 million years; it either evolves into a new species or goes extinct. When paleontologists compare the temporal overlap of several fossils at once, looking for presence, abundance, and absence, they can more precisely pinpoint the exact age of a rock layer.

How long is 4.6 billion years? 4,600,000,000.

That is a HUGE number! Just how big is it really? Big numbers are hard for humans to understand. They are just too big. To help you get a feel for some big numbers, we are going to compare them to everyday things.

• How much space would one million pennies take?

o One million pennies would make a wall 5’ high, 4’ long, and 1’ thick and would weigh 6,300 pounds!

• How much space would one billion pennies take?

o One billion pennies would be larger than 5 school busses!

• How tall are one billion one-dollar bills?

o The stack of bills would be 56.8 miles tall.

• How long are one million seconds?

o One million seconds are 1 week, 4 days, 13 hours, 46 minutes, and 40 seconds.

• How long are one billion seconds?

o One billion seconds are 31 years, 259 days, 1 hour, 46 minutes, and 40 seconds.

• How many thick would one billion pieces of paper be?

o The paper would be 2,189 football fields long!

First, you are each going to develop your own fossil record with the provided handouts. One handout has pictures of two or three organisms in each group of fish (bony rayfinned, bony lobefinned, cartilaginous (sharks), and jawless), amphibians (for example, frogs, salamanders), reptiles (for example lizards, snakes, turtles, dinosaurs), birds (flightless, like ostriches and flight, like pigeons) and mammals (for example rats and humans). One is the fossil and indicated by how old is the first fossil found, and the other is the extant (means still alive today) member of the group.

Cut out each picture of the fossil and related living relative. Locate the age on your timeline of each fossil as indicated on the picture, and glue it to the right of the date. When you have finished gluing your fossils to the correct time, glue all the extant species in the “Recent” area of your timeline. Use a different color pencil and connect the date and the picture of the fossil, like the example Ventastega on the sample timeline. Finally, color-code the extinct and living animals. Circle or connect the fossil to its living relative.

When you have finished your own fossil record, you can help with the class model.

We are also going to create a giant timeline for your classroom, to make a model by converting one million years to one millimeter. (1,000,000 years = 1mm) How big is one millimeter? Look at your ruler. If you look carefully between the 0 and 1 centimeter (cm), you can see 10 lines. Each space between those lines is approximately 1 millimeter.

We are going to measure 4 Eons (very long times) Eras (The Phanerozoic is divided into 3 Eras), and then we are going to measure Periods within each Era (with a total of 11, 2 in Cenozoic – age of mammals, 3 in the Mesozoic – age of dinosaurs, and 6 in the Paleozoic, age of fish).

The Phanerozoic marks the first evidence of multi-cellular organisms to now (green marker):

Write down time ending: 545

Subtract the time starting: 0

How long is your line? 545 mm

There are three Eons in the Precambrian, the time of single cell life and before cells:

Proterozoic (use a brown marker):

Write down time ending: 2,500

Subtract the time starting: 545

How long is your line? 1,955 mm

Archean (use a red marker):

Write down time ending: 3,800

Subtract the time starting: 2,500

How long is your line? 1,300 mm

Hadean (use a black marker):

Write down time ending: 4,500

Subtract the time starting: 3,800

How long is your line? 700 mm

Measure each Eon and draw (with the color Phanerozoic

marker indicated above) a line across the paper,

label each section of (with the color marker

indicated above name with the proper Eon. Proterozoic

Archean

Hadean

Next, you need to mark off the Eras in the Phanerozoic. (We will not be marking of Eras in the Precambrian.) This time, you do the math to figure out how big each era will be:

Cenozoic:

Ending time: 65

Subtract starting time: ___0

How long is your line? mm

Mesozoic:

Ending time: 245

Subtract starting time: __65

How long is your line? mm

Paleozoic:

Ending time: 545

Subtract starting time: _245

How long is your line? mm

To complete your classroom timeline, you need to subdivide each of the Eras into Periods (please see the timeline on Page 7 as an example). You will begin by measuring from the beginning of the Paleozoic at 545 mya, and work your way to the Cenozoic at the top of the paper. ]

Paleozoic: The Age of Fish

• 50mm (from 545 to 495mya), draw a line across the paper, and label “Cambrian.”

• 55mm (from 495 to 440mya), draw a line across the paper, and label “Ordovician.”

• 20mm (from 440 to 420mya), draw a line across the paper, and label “Silurian.”

• 65mm (from 420 to 355mya), draw a line across the paper, and label “Devonian.”

• 65mm (from 355 to 290mya), draw a line across the paper, and label “Carboniferous.”

• 45mm (from 290 to 245mya), draw a line across the paper, and label “Permian.”

Mesozoic: Age of Dinosaurs

• 40mm (from 245 to 205mya), draw a line across the paper, and label “Triassic.”

• 65mm (from 205 to 140mya), draw a line across the paper, and label “Jurassic.”

• 75mm (from 140 to 65mya), draw a line across the paper, and label “Cretaceous.”

Cenozoic: Age of Mammals

• 40mm (from 65 to 25mya), draw a line across the paper, and label “Paleogene.”

• 20mm (from 25 to 5mya), draw a line across the paper, and label “Neogene.”

• Label the remaining 5mm as “Recent.”

Now you are going to fill in the details of your classroom timeline with vertebrate fossils – recording the first fossils evidence of each group you dissected in our class. Locate on the age of each fossil found on your classroom timeline and glue it by that date. All the extant species need to be glued as close to the “Recent” area of your timeline.

Using different color marker, connect the date and the picture of the fossil, the same as you did with your handout.

The pictures below are grouped in pairs belonging to the same Classes (i.e. Amphibia, Mammalia, etc.) with the exception of birds. The top picture is the oldest known member of the Class, together with the time of the first fossil evidence. Cut out each picture on the solid line. For each fossil, locate where it belongs on the time line and mark that spot. Paste the picture of the fossil near that spot, and draw a line from the spot on the timeline to your picture. See the example of the transitional fossil, Ventastega curonica, that has many fish-like and also has many amphibian characteristics.

Calculations:

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Name:

Answer the following questions about your fossils on the timeline:

What is the order, from the oldest (bottom of the paper) to the youngest (top of the paper) vertebrate fossil, how many MYA (million years ago) did it live, and what is the period in which it lived?

FOSSIL

1. ____________________________

2. ____________________________

3. ____________________________

4. ____________________________

5. ____________________________

6. ____________________________

7. ____________________________

8. ____________________________

MYA

_______

_______

_______

_______

_______

_______

_______

_______

PERIOD

___________________

___________________

___________________

___________________

___________________

___________________

___________________

___________________

Which is the youngest fossil?

Which is the oldest fossil?

In this section, write your observations about this timeline, the order of the fossils, how the fossils change as to go from the bottom of the page to the top of the page, and anything else you may have observed.

Answer the following questions about your fossils on the timeline:

What is the order, from the oldest (bottom of the paper) to the youngest (top of the paper) vertebrate fossil, how many mya (million years ago) did it live, and what is the period in which it lived.

FOSSILS

1.

2.

3.

4.

5.

6.

7.

8.

MYA

PERIOD

__________________

__________________

__________________

__________________

__________________

__________________

__________________

__________________

Which is the youngest fossil?

What is the oldest fossil?

In this section, write your observations about this timeline, the order of the fossils, how the fossils change as to go from the bottom of the page to the top of the page, and anything else you may have observed.

-----------------------

Ventastega curonica

365 mya

Looked like a crocodile with a fin on it’s back! Described 2008

Early Cartilage Fish

455 MYA

Modern Shark

Hammerhead

Early Birds

150 mya

Ventastega curonica

365 mya

Looked like a crocodile with a fin on it’s back! Described 2008

Archeoptryx (a bird)

150 Million Years Ago

Archeoptryx

150 mya

Classroom set

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