Unit E Lesson E18 Determining the Age of Artifacts
Completion requirements
Lesson E18: How Old is That?
Video Lesson
Paleontologists and other scientists use some fascinating methods to help them determine the age of things. Their cool lab experiments and fun puzzles of interlocking pieces help to explain important events in Earth’s past. Every new discovery moves us
closer to a better understanding of our ancient world.
Lesson E18: How Old is That?
How Old is That?
Paleontologists and other scientists who study ancient history face many challenges when deciding on the age of the items they find. They can use clues to help determine the age of a newly found object, but knowing exactly how old something is can be almost impossible. Scientists first compare the new discovery to previous finds to determine which is older and which is younger. Then, they can use technology to support their age inferences.
Paleontologists and other scientists who study ancient history face many challenges when deciding on the age of the items they find. They can use clues to help determine the age of a newly found object, but knowing exactly how old something is can be almost impossible. Scientists first compare the new discovery to previous finds to determine which is older and which is younger. Then, they can use technology to support their age inferences.
Reading and Materials for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Pages 414
Materials:
No other materials are required for this lesson.
Of the most important fossils humans have found so far, two Canadian discoveries are near the top of the list. Both are amazing because they show a wide variety of organisms from some of the earliest times of complex forms of life.
Mount Burgess, near Lake Louise in British Columbia, is one of these locations. Burgess Shale is a formation of rocks on the mountain that contains fossils of sea creatures that are 500 million years old. These fossils are amazing because often they include the soft parts of organisms. That is rare for any fossil! In 2014, another huge fossil find was made 40 km south of the Burgess Shale. This might be an even larger source of fossils from these same early times.
Mount Burgess, near Lake Louise in British Columbia, is one of these locations. Burgess Shale is a formation of rocks on the mountain that contains fossils of sea creatures that are 500 million years old. These fossils are amazing because often they include the soft parts of organisms. That is rare for any fossil! In 2014, another huge fossil find was made 40 km south of the Burgess Shale. This might be an even larger source of fossils from these same early times.
Figure E.4.18.1 – The layers of shale on Mount Burgess have been dated at 500 million years ago. The fossils they contain are perhaps the most important fossils ever found. Photo by
Edna Winti.
Figure E.4.18.2 – Opabinia was a soft-bodied sea creature that lived on Earth 500 million years ago. This fossil of Opabinia was found in the Burgess Shale.
Figure E.4.18.3 – The detail of the Opabinia fossils is so good that it allowed detailed models to be made showing the amazing structure of the creature. Illustration by
Nobu Tamura.
Lesson Activity
How Old is That?
Determining the age of a fossil requires careful observation. The fossil, the rock in which it is found, and the location of the rock are all very important in estimating a fossil’s age. Even then, someone might make a new discovery tomorrow that will change everything you thought you knew about your fossil.
Download:
Instructions:
Determining the age of a fossil requires careful observation. The fossil, the rock in which it is found, and the location of the rock are all very important in estimating a fossil’s age. Even then, someone might make a new discovery tomorrow that will change everything you thought you knew about your fossil.
Download:
- DOWNLOAD this document. It has the worksheets where you can record your Observations and Inferences for Two Unknown Fossils. It also has spaces for you to write answers to questions later in this activity.
Instructions:
- Print the How Old is That? worksheets (link to the document is above.)
- Every time you see FOSSIL CHECK, on your worksheets record one or two observations you have about the unknown fossils. Then, make one or two inferences that relate to your observation(s).
- Later in this lesson, you will compare your worksheets to another set of observations, and you will answer some questions.
Figure E.4.18.4 – The photo of unknown fossil A provided by
Smith609. The photo of unknown fossil B provided by
Mistakenpoint.
FOSSIL CHECK: START
Please take out your How Old Is That? worksheet and complete the first row of observations and inferences for the two unknown fossils. Make one or two observations; then, add one or two inferences based on those observations. Part of the first set of observations and inferences has been done for you.
Please take out your How Old Is That? worksheet and complete the first row of observations and inferences for the two unknown fossils. Make one or two observations; then, add one or two inferences based on those observations. Part of the first set of observations and inferences has been done for you.
Relative Age of Fossils and Rocks
A very important part of determining the age of a fossil is realizing that older layers of rock usually are found below younger layers. Sedimentary rock forms from layers of particles building slowly over time.. The most recent layer of sediment forms on top of older layers. Exceptions occur when sedimentary rock layers are folded and faulted, but usually a location nearby shows the original undisturbed layers.
Relative age refers to how old something is in relation to something else. Words such as “young” or “newer” or “late” are used to describe something that has formed recently. Relative aging compares the ages of things without knowing exactly how old they are. “You look younger than that person does, but he seems older than your father is.”
A very important part of determining the age of a fossil is realizing that older layers of rock usually are found below younger layers. Sedimentary rock forms from layers of particles building slowly over time.. The most recent layer of sediment forms on top of older layers. Exceptions occur when sedimentary rock layers are folded and faulted, but usually a location nearby shows the original undisturbed layers.
Relative age refers to how old something is in relation to something else. Words such as “young” or “newer” or “late” are used to describe something that has formed recently. Relative aging compares the ages of things without knowing exactly how old they are. “You look younger than that person does, but he seems older than your father is.”
Figure E.4.18.5 – Rock layers below other rock layers are older than those above them.
When fossils are found, identifying the rock layers is important. If the fossils are found loose on the ground, such as those in the Burgess Shale, paleontologists try to match the rock’s colour and composition to a known rock layer nearby. This task
can be very challenging when glaciers or other methods of erosion move rocks far from their original location.
We do not know the age of the layers of rock in the activity of this lesson (How Old is That?). However, the rock layers just below the fossils show long scrapes and gouges from glaciers, and the layer just above the fossils contains particles of ash from a volcanic eruption.
We do not know the age of the layers of rock in the activity of this lesson (How Old is That?). However, the rock layers just below the fossils show long scrapes and gouges from glaciers, and the layer just above the fossils contains particles of ash from a volcanic eruption.
Figure E.4.18.6 – The oldest rocks on this map are from the Precambrian Era and are labelled red and pink. Purple is rock from the Paleozoic, green is from the Mesozoic, and yellow is from the Cenozoic.
FOSSIL CHECK #1
Please go to your How Old Is That? worksheet and complete the second row. Make one or two observations; then, one or two inferences based on those observations.
Please go to your How Old Is That? worksheet and complete the second row. Make one or two observations; then, one or two inferences based on those observations.
Figure E.4.18.7 – Places such as the Grand Canyon and Alberta’s Badlands help geologists and paleontologists study large sections of strata.
Rock Strata
The rock that surrounds a fossil is usually the most important factor in determining the age of the fossil. The fossil layer of rock, or the layers next to it, may contain valuable age clues. Several layers of rock found together (rock strata) simplify the task because, when a layer is identified, the observer then knows the relative age of the layers above and below. Paleontologists and geologists use rock strata as their primary method of determining rock layer age..
The unknown fossils in this lesson’s activity (How Old is That?) come from the same general location. The rock layers in which they are found are mudstone and sandstone. Because the particles of these layers are very small, most likely the rocks and fossils formed in deep ocean water. The fossil layer is above a layer with glacier erosion, and it is below a layer that contains volcanic ash. In fact, paleontologists believe the volcanic ash might be responsible for the death of the fossil organisms.
The rock that surrounds a fossil is usually the most important factor in determining the age of the fossil. The fossil layer of rock, or the layers next to it, may contain valuable age clues. Several layers of rock found together (rock strata) simplify the task because, when a layer is identified, the observer then knows the relative age of the layers above and below. Paleontologists and geologists use rock strata as their primary method of determining rock layer age..
The unknown fossils in this lesson’s activity (How Old is That?) come from the same general location. The rock layers in which they are found are mudstone and sandstone. Because the particles of these layers are very small, most likely the rocks and fossils formed in deep ocean water. The fossil layer is above a layer with glacier erosion, and it is below a layer that contains volcanic ash. In fact, paleontologists believe the volcanic ash might be responsible for the death of the fossil organisms.
Figure E.4.18.8 – Layers of sedimentary rock are referred to as strata.
The rock strata with the volcanic ash layer has been identified in other parts of the world. Where this strata was found in England, the rocks were found to be as old as Precambrian Era. This is quite amazing for our unknown fossils. That means our unknown
fossils could be some of the earliest examples ever found of complex life.
FOSSIL CHECK #2
On your How Old Is That? worksheet, complete the third row. Make one or two observations; then, one or two inferences based on those observations.
On your How Old Is That? worksheet, complete the third row. Make one or two observations; then, one or two inferences based on those observations.
Index Fossils
So far, you have learned how to estimate the relative age of rocks and fossils by comparing sedimentary layers and rock strata. However, making a good guess at fossil age is impossible unless you have a very accurate record of every layer of rock around the world. Scientists and amateurs have been studying rock layers and fossils long enough to have produced an accurate record of every layer. Thus, other methods must be used.
Index fossils are the first method. Index fossils came from large, widespread populations of organisms, but they lived on Earth only for short periods. Their appearance in a rock layer anywhere on Earth signals a very specific range of time.
For example, humans would be a very good index fossil right now. If you find any rocks with human fossils in them, the rocks cannot be more than a few million years old. If you find a Tyrannosaurus rex bone beside a human bone in a layer of rock, somebody is playing a joke on you! Humans and T. rex did not live on Earth at the same time, and humans are an index fossil for rocks that are very young.
So far, you have learned how to estimate the relative age of rocks and fossils by comparing sedimentary layers and rock strata. However, making a good guess at fossil age is impossible unless you have a very accurate record of every layer of rock around the world. Scientists and amateurs have been studying rock layers and fossils long enough to have produced an accurate record of every layer. Thus, other methods must be used.
Index fossils are the first method. Index fossils came from large, widespread populations of organisms, but they lived on Earth only for short periods. Their appearance in a rock layer anywhere on Earth signals a very specific range of time.
For example, humans would be a very good index fossil right now. If you find any rocks with human fossils in them, the rocks cannot be more than a few million years old. If you find a Tyrannosaurus rex bone beside a human bone in a layer of rock, somebody is playing a joke on you! Humans and T. rex did not live on Earth at the same time, and humans are an index fossil for rocks that are very young.
Figure E.4.18.9 – Index fossils are similar to signposts along the road to learning the age of a rock layer.
We can use index fossils for this lesson’s activity (How Old is That?). One of the best index fossils is the trilobite. Trilobites were sea creatures that lived in ancient oceans all over the world. Trilobite fossils are very common in many rocks. However,
trilobites changed in very distinctive ways over time. When a trilobite fossil is found, the body parts are studied very closely. Matching trilobites allow scientists to match and age rock layers around the world.
As we know, the distinctive rock strata our unknown fossils is found in England, also. The location in which our unknown fossils were found was heavily eroded so that information has been lost. But this was not the case in England. The rock layers above the fossil layer in England did not erode, and they contain some of the earliest trilobite fossils ever found. Trilobites do not appear in the fossil record until the beginning of the Paleozoic Era, just after the end of Precambrian times.
As we know, the distinctive rock strata our unknown fossils is found in England, also. The location in which our unknown fossils were found was heavily eroded so that information has been lost. But this was not the case in England. The rock layers above the fossil layer in England did not erode, and they contain some of the earliest trilobite fossils ever found. Trilobites do not appear in the fossil record until the beginning of the Paleozoic Era, just after the end of Precambrian times.
Figure E.4.18.10 – Trilobites are very useful index fossils throughout the Paleozoic Era.
FOSSIL CHECK #3
On your How Old Is That? worksheet, complete the fourth row. Make one or two observations; then add one or two inferences based on those observations.
On your How Old Is That? worksheet, complete the fourth row. Make one or two observations; then add one or two inferences based on those observations.
Figure E.4.18.11 – The Badlands near Drumheller show rock strata that include a dark band of rocks separating the Mesozoic and Cenozoic eras.
Absolute Age of Fossils and Rocks
Index fossils help paleontologists to narrow the age of a fossil and the rock layer in which it is found. However, how do they know the age of the index fossil? No way is available to find the exact age of a fossil, but rocks are different. Imagine picking up a rock randomly from the road and asking someone how old that rock is. The answer could be 100 years old or 1 billion years old. Is there a way to measure the actual age of a rock?
The answer is “yes” -- as long as the rock contains radioactive materials. Radioactive material breaks down at very predictable rates. This rate is measured using a unit called a half-life. For example, suppose you have something with a half-life of 5 years that is worth $1000. In five years, it will be worth half that, or $500. In another five years (its half-life), that material will be worth only $250, and so on.
Index fossils help paleontologists to narrow the age of a fossil and the rock layer in which it is found. However, how do they know the age of the index fossil? No way is available to find the exact age of a fossil, but rocks are different. Imagine picking up a rock randomly from the road and asking someone how old that rock is. The answer could be 100 years old or 1 billion years old. Is there a way to measure the actual age of a rock?
The answer is “yes” -- as long as the rock contains radioactive materials. Radioactive material breaks down at very predictable rates. This rate is measured using a unit called a half-life. For example, suppose you have something with a half-life of 5 years that is worth $1000. In five years, it will be worth half that, or $500. In another five years (its half-life), that material will be worth only $250, and so on.
Figure E.4.18.12 – Samples from radioactive materials are taken to a lab for analysis and aging.
Similar to index fossils, the most useful radioactive rock layers are those that are widespread and contain unique radioactive materials. The best examples of this are meteorite dust and volcanic ash. When we can label a rock layer and its fossils with
a specific age, we say it has an absolute age.
The most famous extinction in Earth’s history is probably the disappearance of almost all species of dinosaurs 66 million years ago. Dinosaurs had been living very successfully on Earth for more than 100 million years, and then they disappeared suddenly. Scientists have noted a thin rock layer just above the last dinosaur fossils all over the world. It contains a very rare radioactive material usually found only in meteorites and asteroids. Because this is a radioactive layer, the half-life can be used to estimate its age very accurately. That is why scientists believe the extinction of the dinosaurs occurred 66 000 000 years ago.
Other radioactive rock layers are used as signposts of absolute ages. The unknown fossils in this lesson’s activity (How Old is That?) were buried in volcanic ash, and that allows scientists to determine an absolute age for that ash layer. As suspected, those unknown fossils were found in rocks that are more than 600 million years old.
The most famous extinction in Earth’s history is probably the disappearance of almost all species of dinosaurs 66 million years ago. Dinosaurs had been living very successfully on Earth for more than 100 million years, and then they disappeared suddenly. Scientists have noted a thin rock layer just above the last dinosaur fossils all over the world. It contains a very rare radioactive material usually found only in meteorites and asteroids. Because this is a radioactive layer, the half-life can be used to estimate its age very accurately. That is why scientists believe the extinction of the dinosaurs occurred 66 000 000 years ago.
Other radioactive rock layers are used as signposts of absolute ages. The unknown fossils in this lesson’s activity (How Old is That?) were buried in volcanic ash, and that allows scientists to determine an absolute age for that ash layer. As suspected, those unknown fossils were found in rocks that are more than 600 million years old.
FOSSIL CHECK #4
In your How Old is That? worksheet, complete the fifth row. Make one or two observations; then, add one or two inferences based on those observations.
In your How Old is That? worksheet, complete the fifth row. Make one or two observations; then, add one or two inferences based on those observations.
Figure E.4.18.13 – The various layers of rock at Mistaken Point represent many layers of deep, ancient ocean floor.
Mistaken Point, Newfoundland
The study of ancient life is complex and difficult. A new fossil or radioactive layer helps scientists understand more, and it can change what they thought was correct the day before. The discovery of fossils in Mistaken Point, Newfoundland, was one of those big discoveries.
The unknown fossils in this lesson’s activity (How Old is That?) are from Mistaken Point. They were found 50 years ago by a university student named Shiva Balak who wanted to be a geologist. As he was exploring the southeastern coast of Newfoundland, he found some strange fossils. He was surprised by the complexity of the fossils because he realized the age of the rocks in which the fossils were found. These were rocks from the Precambrian Era, and up until that time, scientists believed that all life in the Precambrian Era were simple single-celled organisms that floated in the water.
The study of ancient life is complex and difficult. A new fossil or radioactive layer helps scientists understand more, and it can change what they thought was correct the day before. The discovery of fossils in Mistaken Point, Newfoundland, was one of those big discoveries.
The unknown fossils in this lesson’s activity (How Old is That?) are from Mistaken Point. They were found 50 years ago by a university student named Shiva Balak who wanted to be a geologist. As he was exploring the southeastern coast of Newfoundland, he found some strange fossils. He was surprised by the complexity of the fossils because he realized the age of the rocks in which the fossils were found. These were rocks from the Precambrian Era, and up until that time, scientists believed that all life in the Precambrian Era were simple single-celled organisms that floated in the water.
Figure E.4.18.14 – One of the most important fossil discoveries in all paleontology occurred at Mistaken Point, Newfoundland. Photo by
EOL Learning and Education Group.
However, these fossils were not simple or single-celled, and they were found in Precambrian rocks. So little is known about these fossil organisms that paleontologists are not even sure if they were plants, animals, or some other type of organism that
is no longer on Earth.
This discovery of these complex life forms from the Precambrian era caused changes to the geologic time scale and fossil record, and scientists had to rethink how life changed at the beginning of the Paleozoic Era.
This discovery of these complex life forms from the Precambrian era caused changes to the geologic time scale and fossil record, and scientists had to rethink how life changed at the beginning of the Paleozoic Era.
Lesson Activity: End
How Old is That?
Instructions:
Instructions:
- You should have already downloaded and completed the How Old is That? worksheet. If you have not done so, go back in this lesson to find the start of the activity and follow the directions.
- Compare the observations and inferences on your worksheet to this completed worksheet. Every scientist makes different observations and inferences, so yours can be different, too. Use both completed worksheets to answer the questions.
Questions:
Think about the following questions very carefully; then, type or write your answers. When you have your answers, click the questions for feedback.
Think about the following questions very carefully; then, type or write your answers. When you have your answers, click the questions for feedback.
The first inference most people have is that these are plant fossils and that they are old. They have the shape and design of familiar plants and we recognize fossils as being old, but there is no way to know how old.
To know why these fossils are important just by looking at them is difficult. Perhaps, they are the first or last plants to be found in a certain era, or they might be organisms that are used to prove a concept such as Pangaea.
What are some of the most important observations that can be made when a fossil is first discovered?
Where the fossil is found is sometimes as important as the fossil itself. The rocks in which the fossil are found must be observed closely to help paleontologists to make inferences about a fossil.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to
guide your learning.
Unit E Lesson 18 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
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REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Self-Check Time!
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Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
Rock layer A is probably the youngest layer because it is closest to the surface. Rock layer G is probably the oldest because it is the deepest layer. We say probably because we cannot see the surrounding rock layers, and it is possible that some geologic event occurred to flip all the layers upside down.
On the map, Alberta is in the Western Canadian Sedimentary Basin. This is a huge swimming-pool shaped depression in the crust that was filled with layers of sediment over hundreds of million of years. In this swimming-pool basin, the deep end is near the Rocky Mountains and the shallow end is in Saskatchewan. A core sample drilled from any yellow area probably would show Precambrian rocks (red on the map) at the very bottom of the core, then above that, rock from the Paleozoic Era (purple on the map), then rock from the Mesozoic Era (green), and finally Cenozoic rock (yellow on the map) that was deposited most recently.
Igneous rocks are exposed to large amounts of heat. Heat destroys most fossils. Trace fossils might form from an unlucky animal that tried to walk through or fell into lava flowing from a volcano. The age of the igneous fossil could be determined by the sedimentary layers it flows over and by which it is covered later. Igneous fossils could be dated by the volcanic ash from the volcano that matches chemically the igneous rock from the same eruption.
Most fossils are from animals with skeletons, plates, armour, or other hard parts. In its lifetime, one trilobite might shed its hard shell several times, possibly leaving a fossil every time.
The geologic time scale represents all the observations and inferences made by geologists, paleontologists, and other scientists about Earth’s history. The start and end of the many divisions in the geologic time scale are defined usually by major events in Earth’s history. This makes sense, but it also makes life easier for scientists because a change that they can infer from their observations might be a large volcanic eruption that caused extinctions and left an index fossil that might change suddenly because of climate change or a breakup of a supercontinent. There is no way to know for certain if the geologic time scale will be changed in the future. Because new discoveries have caused it to be changed many times in the past, adjustment in the future is very likely.