Unit E Lesson E14 Fossil Evidence
Completion requirements
Lesson E14: Fossil Evidence in the Earth's Crust
Video Lesson
Fossils are the clues and remains left behind by organisms that lived long ago. Learning from fossils is a great way to learn about Earth’s past. Scientists such as paleontologists locate and examine carefully fossils for any information they can give
us about conditions on Earth many years ago.
Watch the following two videos to learn about the different fossil types, and how they are collected and prepared.
Watch the following two videos to learn about the different fossil types, and how they are collected and prepared.
Lesson E14: Fossil Evidence in the Earth's Crust
Fossils
Trillions of living things have existed on Earth during the past 4 billion years, but most of these organisms have not left fossils. In most places on Earth, only rarely are fossils found – and never in many other places. However, Alberta is special in this way. The formation of the Rocky Mountains and the presence of warm, shallow seas resulted in Alberta becoming a terrific place to preserve signs of ancient life. Deep layers of sedimentary rock rich in eroded materials flowing from the young mountains help to protect the fossilized remains of many plants and animals for many millions of years.
Trillions of living things have existed on Earth during the past 4 billion years, but most of these organisms have not left fossils. In most places on Earth, only rarely are fossils found – and never in many other places. However, Alberta is special in this way. The formation of the Rocky Mountains and the presence of warm, shallow seas resulted in Alberta becoming a terrific place to preserve signs of ancient life. Deep layers of sedimentary rock rich in eroded materials flowing from the young mountains help to protect the fossilized remains of many plants and animals for many millions of years.
Reading and Materials for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Pages 410–413
Materials:
newspaper, plate, clay or dough, small objects for fossils, petroleum jelly, small paintbrush, plaster of paris or white glue
Figure E.4.14.1 – Work where the fossils are found can take months to complete.
Figure E.4.14.2 – Fossils are hard to find; they are buried in layers of sedimentary rock until they become exposed.
Fossils, Paleontologists, Geologists, and Biologists
Earth’s history is interesting in many ways. One way is how paleontologists, the scientists who study ancient life, collaborate with geologists, the scientists who study rocks and Earth. Paleontologists and geologists work together to understand ancient life and Earth’s past. Some very simple observations and some complicated measurements allow these groups of scientists to learn about Earth’s past.
Earth’s history is interesting in many ways. One way is how paleontologists, the scientists who study ancient life, collaborate with geologists, the scientists who study rocks and Earth. Paleontologists and geologists work together to understand ancient life and Earth’s past. Some very simple observations and some complicated measurements allow these groups of scientists to learn about Earth’s past.
To understand this, imagine you found two fossils in a riverbank near your home. One is near the top of the bank, and the other is down near the water. Your first reaction is to dig them out, but then you realize there might be some valuable evidence
based on where they are right now, so you do not dig. When you examine the fossils closely, you notice they are stuck in different layers of sedimentary rock. You realize quickly that the fossil in the lower layer is probably much older than the fossil
near the surface. This is because the layers of sedimentary rock are deposited on top of each other over very long periods. When a paleontologist and some assistants arrive to examine your discovery, they agree with you. What they do not know, however,
is the age of each layer of rock. They can assume the age of the fossil is the same as the age of the layer. Then, a geologist arrives.
The geologist is a rock expert who notices a special layer that is between the layers that have the fossils. This special layer is found all over the province, and it is special because it contains mostly volcanic ash. A long time ago, a volcano erupted and left a layer of ash over most of what is now Alberta.
The geologist is a rock expert who notices a special layer that is between the layers that have the fossils. This special layer is found all over the province, and it is special because it contains mostly volcanic ash. A long time ago, a volcano erupted and left a layer of ash over most of what is now Alberta.
Figure E.4.14.3 – The banks of rivers and streams can erode away to expose fossils.
Scientists have determined that layer is 20 million years old (you will learn how this is done in a future lesson). Therefore, at the very least, you know your top fossil is younger than 20 million years and your bottom fossil is older than 20 million
years.
One of the first tasks when fossils are found is to identify them. Many younger fossils are similar to plants and animals that are alive today. But many older fossils look different than any organisms alive now. These are fossils of extinct organisms, and paleontologists must try to identify the fossils and other organisms they are closely related to.. If the paleontologists are fortunate to find a bone, blood, hair, or other body part that contains DNA, biologists can help by doing a DNA analysis on a sample of the fossil.
Fossils and rocks together allow paleontologists and geologists to understand better Earth’s past. Of course, fossils and rocks are found close together.. Without rock protecting and saving the fossil, most signs of ancient life would be lost forever.
One of the first tasks when fossils are found is to identify them. Many younger fossils are similar to plants and animals that are alive today. But many older fossils look different than any organisms alive now. These are fossils of extinct organisms, and paleontologists must try to identify the fossils and other organisms they are closely related to.. If the paleontologists are fortunate to find a bone, blood, hair, or other body part that contains DNA, biologists can help by doing a DNA analysis on a sample of the fossil.
Fossils and rocks together allow paleontologists and geologists to understand better Earth’s past. Of course, fossils and rocks are found close together.. Without rock protecting and saving the fossil, most signs of ancient life would be lost forever.
Figure E.4.14.4 – Fossils can reveal many important clues about ancient life and the Earth.
Figure E.4.14.5 – Fossils trapped in ice, sap, or amber can preserve an entire specimen. These are very rare and very valuable to paleontologists.
Figure E.4.14.6 – Almost all fossils are trapped in sedimentary rock. This type of rock is not exposed to high heat or pressure, and sediments help protect delicate fossil structures.
How and Where Fossils Form
Fossils are any traces or remains left behind by a living thing in the distant past. The newest fossils are about 10 000 years old. The oldest are almost 4 billion years old. Fossils can be the preserved remains of an actual organism, an imprint of an organism’s bones or leaves, or the organism’s tracks preserved in what was a muddy plain. To a paleontologist, every fossil is a clue that links all other fossils into a record of Earth’s past. In fact, all fossils become a part of a collection of Earth’s past called the fossil record.
Almost all fossils are found in sedimentary rock. Sedimentary rock forms slowly from layers of silt and sand. Because sedimentary rocks usually form at the bottom of shallow lakes and seas, most fossils are from plants and animals that lived in or very near the water.
Fossils are any traces or remains left behind by a living thing in the distant past. The newest fossils are about 10 000 years old. The oldest are almost 4 billion years old. Fossils can be the preserved remains of an actual organism, an imprint of an organism’s bones or leaves, or the organism’s tracks preserved in what was a muddy plain. To a paleontologist, every fossil is a clue that links all other fossils into a record of Earth’s past. In fact, all fossils become a part of a collection of Earth’s past called the fossil record.
Almost all fossils are found in sedimentary rock. Sedimentary rock forms slowly from layers of silt and sand. Because sedimentary rocks usually form at the bottom of shallow lakes and seas, most fossils are from plants and animals that lived in or very near the water.
Figure E.4.14.7 – Exposed sedimentary rocks provide the best access to buried fossils.
When the organism dies, or when it leaves behind a scratch or a track, sediments cover it or fill it. If the conditions are right, and nothing breaks apart the remains or trace, the fossil can form. If the living things have hard parts, such as shells
and bones, they are more likely to leave fossils. Fossils of soft-bodied creatures such as worms and jellyfish are very rare.
Fossils are very difficult to find. Most sedimentary rock does not have fossils in it that we can see. To reveal a fossil, a break in the rock must be in just the right place so the fossil appears. Because of the way sedimentary rock forms, we can assume
that most fossils are of creatures buried very quickly by sediments, such as would occur in a mudslide or flood. The chance that the remains of a living thing or its tracks would last for the hundreds of years it might take to bury it in normal river
or sea sediment is very small. The potential fossil would be scavenged, decomposed, or broken apart – and disappear forever.
Although most fossils are formed in the sea, almost all fossils are found on land. Places such as Alberta and central North America, which were once covered in a shallow sea, are prime areas to find fossils. Sometimes sedimentary rock is pushed high into the air during mountain building. One of the most amazing fossil discoveries ever made was in the Burgess Shale of British Columbia, high on the side of a mountain. The fossils found there are all ocean creatures!
Although most fossils are formed in the sea, almost all fossils are found on land. Places such as Alberta and central North America, which were once covered in a shallow sea, are prime areas to find fossils. Sometimes sedimentary rock is pushed high into the air during mountain building. One of the most amazing fossil discoveries ever made was in the Burgess Shale of British Columbia, high on the side of a mountain. The fossils found there are all ocean creatures!
Figure E.4.14.8 – Some fossils preserve large amounts of detail.
Figure E.4.14.9 – The imprint of a seashell has left behind a mold fossil.
Figure E.4.14.10 – This fossil is petrified coral.
Figure E.4.14.11 – A spider fossil trapped in amber.
Figure E.4.14.12 – Footprints are trace fossils.
Types of Fossils
1. Casts and molds form when a living thing is buried in sediments. The original organism decays and disappears, but the impression it leaves in the sediment remains. If the impression stays empty, the fossil is called a mold. If some other sediment or mineral later fills the mold, we call the fossil a cast.
2. Trace fossils are the tracks, scratches, or other marks left by living things. These can become casts or molds, but they are called trace fossils because they do not contain the actual living things.
3. Actual remains are very rare fossils. These “true-form” fossils usually are formed when organisms become trapped in liquids that harden, such as ice, tree sap (amber), or tar.
4. Mineralization occurs when the inside of the remains of living things fill with minerals during the formation of the sedimentary rock. This can occur if rich runoff bathes the remains of the organism soon after it dies. Examples of mineralized fossils include petrified wood and ammolite.
1. Casts and molds form when a living thing is buried in sediments. The original organism decays and disappears, but the impression it leaves in the sediment remains. If the impression stays empty, the fossil is called a mold. If some other sediment or mineral later fills the mold, we call the fossil a cast.
2. Trace fossils are the tracks, scratches, or other marks left by living things. These can become casts or molds, but they are called trace fossils because they do not contain the actual living things.
3. Actual remains are very rare fossils. These “true-form” fossils usually are formed when organisms become trapped in liquids that harden, such as ice, tree sap (amber), or tar.
4. Mineralization occurs when the inside of the remains of living things fill with minerals during the formation of the sedimentary rock. This can occur if rich runoff bathes the remains of the organism soon after it dies. Examples of mineralized fossils include petrified wood and ammolite.
Figure E.4.14.13 – A cast fossil forms in the mold of a nautilus shell.
Index fossils are very important fossils to paleontologists because they help to identify a specific time in the past. This is because the organism was very successful, often with large populations spread over a wide area. However, these organisms did
not live on Earth for very long. Therefore, when these fossils are found, paleontologists know the rocks are from that specific time. Index fossils help provide ages for rocks as well as the fossils found above, below, and nearby.
The most famous index fossils are the ammonites, which were a relative of squid and octopus. They had hard shells, so they formed distinct cast and mold fossils. Ammonites lived on Earth for 300 million years, and they were very successful and widespread, but their shells changed over time. Depending on the shell features, paleontologists can determine the age of the rock the shell was found in – and therefore the age of its neighbours!
The most famous index fossils are the ammonites, which were a relative of squid and octopus. They had hard shells, so they formed distinct cast and mold fossils. Ammonites lived on Earth for 300 million years, and they were very successful and widespread, but their shells changed over time. Depending on the shell features, paleontologists can determine the age of the rock the shell was found in – and therefore the age of its neighbours!
Try It!
Homemade Fossils
Try this simple experiment at home to make your own fossils. Hardening of the fossils so they can be examined takes about 24 hours -- sometimes more. Be patient!
Materials:
Try this simple experiment at home to make your own fossils. Hardening of the fossils so they can be examined takes about 24 hours -- sometimes more. Be patient!
Materials:
- newspaper to prevent mess
- tupperware container or plate
- clay or dough
- small objects for fossils (shells, leaves, cones, etc.)
- petroleum jelly
- small paintbrush
- plaster of paris, repair spackle, or white glue
Download:
DOWNLOAD this document. It provides a space for you to write answers to questions later in this activity.
Instructions:
1. Press clay gently into the bottom of a container to form a layer a few centimetres thick.
2. Use your collection of small objects to make impressions that will become mold, cast, or trace fossils.
3. Use the paintbrush to apply a thin coat of petroleum jelly gently to the impressions that you will make into cast fossils.
4. Add plaster of paris or white glue into the cast fossil impressions that have been coated with petroleum jelly.
5. Leave the glue or plaster to harden for at least 24 hours; wait longer than 24 hours if the mold is deep.
6. When the glue or plaster is dry and hardened, lift the cast of the impression carefully from the mold.
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
The best trace fossils are made when large, distinct impressions are left in the clay. Dinosaur footprints are examples of trace fossils. Therefore, the best objects to use for trace fossils are quite large and heavy.
The best mold fossils usually are made by organisms that have detailed shells or outside body parts. That way, you can learn about the organism from its fossil without any of the original organism. Thus, the best choice for mold fossils are things with
tiny wrinkles and bumps.
The best cast fossils are made from good molds but also from molds that are small. Because a second sediment has to fill the mold and then harden into a cast, a smaller and thinner mold has a better chance of forming a cast in less time.
A mineralized (petrified) fossil would form if we could leave the organism in the clay and fill its body slowly with a mineral solution that would harden into rock eventually. When the organism decays, the petrified fossil remains.
Fossils represent ancient life. Everything used in the photographs here is or was alive. All examples represent what could become real fossils.
Figure E.4.14.14 – Finding a fossil can mean months of work to gently move the surrounding rock. Photo by
UNED.
Figure E.4.14.15 – Many months are required to do the fine work of cleaning the fossil at the laboratory or museum.
Collecting Fossils
The conditions have to be just right to preserve evidence of an ancient form of life. Then, conditions have to be just right for someone to find that fossil millions of years later. Finding a fossil in a layer of sedimentary rock is like finding a needle in a haystack. You hope the thing you are looking for is there, but to find it, you must be very diligent – and perhaps just lucky! Many of the most amazing fossil discoveries have been made by normal people snooping around riverbanks or digging holes in their backyards.
The conditions have to be just right to preserve evidence of an ancient form of life. Then, conditions have to be just right for someone to find that fossil millions of years later. Finding a fossil in a layer of sedimentary rock is like finding a needle in a haystack. You hope the thing you are looking for is there, but to find it, you must be very diligent – and perhaps just lucky! Many of the most amazing fossil discoveries have been made by normal people snooping around riverbanks or digging holes in their backyards.
When you find a fossil, the best thing to do is to call a professional. A paleontologist at the nearest university or museum can contact a team of people who can determine if the object is a fossil and what kind of fossil it might be. Remember that finding
a fossil is like finding a clue at a crime scene. If you remove the clue from the crime scene, the detectives lose the connections the clue has to the scene.The paleontologist will examine the fossil find very carefully for clues to help determine
the kind of fossil and its age as well as other fossils nearby.
The first part of the recovery process involves removing the fossil securely and safely from the surrounding rock. This can take days, weeks, or even months, and sometimes it requires a large slab of rock to be cut around the fossil. When you see paleontologists working at a fossil find, you might see them chiseling gently at rock, digging a trench carefully around the fossil, and brushing away dust gently. Because the rock and fossil can be unstable, a cast (similar to what you use to protect a broken bone) or some sort of protective wrap might be placed securely around the rock. The slab of rock may then be lifted with a large crane or even a helicopter to be transported to a paleontology lab for further work.
The first part of the recovery process involves removing the fossil securely and safely from the surrounding rock. This can take days, weeks, or even months, and sometimes it requires a large slab of rock to be cut around the fossil. When you see paleontologists working at a fossil find, you might see them chiseling gently at rock, digging a trench carefully around the fossil, and brushing away dust gently. Because the rock and fossil can be unstable, a cast (similar to what you use to protect a broken bone) or some sort of protective wrap might be placed securely around the rock. The slab of rock may then be lifted with a large crane or even a helicopter to be transported to a paleontology lab for further work.
Figure E.4.14.16 – Some fossils require extra recovery work before they can be displayed.
Watch More
Sometimes some very impressive technology is used to move fossils from the Badlands back to the Royal Tyrrell Museum.
More delicate work begins after the rock with the fossil inside reaches the lab. The technicians are responsible for removing delicately all the rock from the slab, leaving only the fossil behind. This can take months, and often it requires repairs to crumbling fossils using glue or cement. Most fossils of complex animals have many bones, but those bones usually have fallen from the skeleton and can be mixed up in the rock. Sometimes, the fossil is more valuable to leave within the slab of rock because it shows how all the parts of the organism fit together.
The next time you see a fossil in a museum, you can appreciate the months of work and many people required to prepare that fossil for display. Read the amazing blog of Darren Tanke of the Royal Tyrrell Museum as he works to free a Gorgosaurus from its stony surroundings.
More delicate work begins after the rock with the fossil inside reaches the lab. The technicians are responsible for removing delicately all the rock from the slab, leaving only the fossil behind. This can take months, and often it requires repairs to crumbling fossils using glue or cement. Most fossils of complex animals have many bones, but those bones usually have fallen from the skeleton and can be mixed up in the rock. Sometimes, the fossil is more valuable to leave within the slab of rock because it shows how all the parts of the organism fit together.
The next time you see a fossil in a museum, you can appreciate the months of work and many people required to prepare that fossil for display. Read the amazing blog of Darren Tanke of the Royal Tyrrell Museum as he works to free a Gorgosaurus from its stony surroundings.
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 14 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.
-
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.
Understanding Earth’s past is not easy, but it is possible by linking the rocks that geologists study with the fossils that paleontologists study and that biologists link to living species on Earth today. Each of these sciences provides information from observations; then, educated inferences can be made about Earth’s past.
Paleontologists always want to find fossils, but finding them can be very difficult. Places such as eroded badlands or excavated mines allow seekers to see deep into the sedimentary layers where fossils might be. However, finding a fossil there seems to be luck, too. In places where other fossils are found, however, the conditions might be favourable for more fossils to have formed.
Large floods provide plentiful sediments for burying organisms to become fossils, but large floods are also very destructive. The water bashes anything caught in its path, and most skeletons quickly become scattered bones during a flood.
Several answers are possible. Many dinosaurs were large with large bones that were hard. These can become fossils more easily than soft parts such as skin or muscle. Dinosaur fossils are large, and larger fossils are noticed much more easily than smaller fossils are. Because many dinosaurs lived near swamps and water, their fossils can be found in places that form fossils well. Dinosaurs are popular, and people talk about dinosaur fossils more than they talk of other fossils. Huge populations of dinosaurs were on Earth for hundreds of millions of years, so fossils had many opportunities to form when conditions were right.
The Chinese fossils were formed by large amounts of ash falling near the volcano when it erupted. This is similar to the volcano Vesuvius that buried the town of Pompeii in ash. As long as the heat did not burn the organisms, the ash formed a protective layer that allowed very good fossils to form.