1. Fossils
Chapter 16 Lesson 1
Pages 564 - 572

2. Vocabulary
• Fossil – the preserved remains or evidence of ancient living things
• Catastrophism – the idea that conditions and organisms on Earth
change in quick, violent events
• Uniformitarianism – a principle that states that geologic processes
that occur today are similar to those that have occurred in the past
• Carbon Film – the fossilized carbon outline of an organism or part
of an organism
• Mold – the impression in a rock left by an ancient organism
• Cast – a fossil copy of an organism made when a mold of the
organism is filled with sediment of mineral deposits
• Trace Fossil – the preserved evidence of the activity of an organism
• Paleontologist – scientists who study fossils

3. Evidence of the Distant Past
• Just like old photos, fossils provide us with
clues about Earth’s past
• Fossils are the preserved remain or evidence
of ancient living things

4. Catastrophism
• Many fossils represent plants and animals that are extinct
• In the past many scientists believed that a single, sudden,
catastrophic disaster killed the organisms that become fossil
• Catastrophism is the idea that conditions and organisms on Earth
change in quick, violent events
– These include large volcanic eruptions and widespread flooding

5. Catastrophism
• Scientists eventually disagreed with
catastrophism because Earth’s history is full of
violent events
• Most people who supported catastrophism
thought that Earth was only a few thousand years
old

6. Uniformitarianism
• In the 1700s, James Hutton rejected the idea of
catastrophism
• Hutton thought that the processes responsible for changing
the landscape could also shape Earth’s surface
– For example, he thought that erosion caused by streams could
also wear down mountains
– He realized that these processes would take a long time and
proposed that Earth was much older than a few thousand years

7. Uniformitarianism
• Hutton’s ideas were eventually included in a
principle called uniformitarianism.
– The principle of uniformitarianism states that
geological processes that occur today are similar to
those that have occurred in the past
– According to this view, Earth’s surface is constantly
being reshaped in a steady, uniform manner

8. Uniformitarianism
• Today, uniformitarianism is the basis for understanding
Earth’s past
• But scientists also know that catastrophic event do
sometimes occur
– Huge volcanic eruptions and giant meteorite impacts can
change Earth’s surface quickly and can be explained by
natural processes

9. Fossil Formation
• Not all dead organisms become fossils. More
than likely, you will not become a fossil.
• Fossils form only under certain conditions.

10. Conditions for Fossil Formation
• Most plants and animals are eaten or decay when they die, leaving
no trace that they ever lived
– Consider an apple. More than likely an apple will decay into a soft
lump and be decomposed by bacteria and insects
• Some conditions increase the chances that a fossil will form.
1. If the organism has hard parts, such as shells, teeth, or bones
2. If the organism is buried quickly after it dies.
• This way the layers of sand and mud slow or stop decay

11. Fossils Come in All Sizes
• Many of the fossils we think of are large dinosaur fossils.
• However, not all fossils are large.
• Microfossils are tiny fossils each about the size of a speck
of dust.
– Details of microfossils can be seen only under a microscope

12. Types of Preservation
• Fossil are preserved in many different ways:
– Preserved Remains
– Carbon Films
– Mineral Replacement
– Molds
– Casts
– Trace Fossils

14. Preserved Remains
• Sometimes the actual remains of organisms are
preserved as fossils
• For this to happen, an organism must be completely
enclosed in some material over a long period of time.
– This would prevent it from being exposed to air or
bacteria
– Generally this fossils are less than 10,000 years old.
However insects preserved in amber can be millions of
years old.

15. Carbon Films
• Sometimes when an organism is buried, exposure to
heat and pressure forces gases and liquids out of the
organism’s tissues.
• This leaves only the carbon behind
• A carbon film is the fossilized carbon outline of an
organism or part of an organism

16. Mineral Replacement
• Replicas, or copies, of organisms can form
from minerals in groundwater.
• They fill in the pore spaces or replace the
tissues of dead organisms
• Petrified wood is an example

17. Molds
• Sometimes all that remains of an organism is its fossilized imprint or
impression.
• A mold is the impression in a rock left by an ancient organism
1. First, sediment must harden around a buried organism
2. As the organism decays over time an impression of its shape remains
in the sediment
3. Eventually the sediment turns into rock

18. Casts
• Sometimes, after a mold forms, it is filled with
more sediment,.
• A cast is a fossil copy of an organism made when
a mold of the organism is filled with sediment or
mineral deposits.
Mold
Cast

19. Trace Fossils
• Some animals leaves fossilized traces of their movement or activity
• A trace fossil is the preserved evidence of the activity of an organism
• These include
– Tracks
– Footprints
– Nest
– Droppings
• These fossils help scientists learn about characteristics and behaviors of
animals
– They can reveal clues about an organism’s size, speed, and whether they
traveled alone or in groups

20. Ancient Environments
• Scientists who study fossils are called paleontologists
• Paleontologists use the principle of uniformitarianism to
learn about ancient organisms and their environment
• They often compare fossils of ancient organisms to
organisms living today
– For example, trilobite fossil and horseshoe crabs look alike
– Horseshoe crabs today live in shallow water on the ocean floor
– Partly because trilobite fossils look so much like horseshoe
crabs, paleontologists infer that trilobites also lived in shallow
ocean waters

21. Shallow Seas
• Today, Earth’s continents are mostly above sea level.
• But, sea level has risen, flooding Earth’s continents, many times in
the past
• For example, a shallow ocean covered much of North America 450
million years ago.
• Fossils of organisms that lived in that shallow ocean help scientists
reconstruct what the seafloor looked like at that time.

22. Past Climates
• Evidence indicates that Earth's present-day climate is
warming.
• Fossils show that Earth's climate has warmed and
cooled many times in the past
• Plant fossils are especially good indicators of climate
change
• For example, fossils of ferns and other tropical plants
dating to the time of the dinosaurs reveal that Earth
was very warm 100 million years ago
• Tropical forests and swamps covered much of the land
• Millions of year later, the swamps and forests were
gone, but coarse grasses grew in their place

23. Past Climates
• Huge sheets of ice called glaciers spread over
parts of N. America, Europe, and Asia.
• Fossils suggest that some species that lived
during this time, such as the woolly mammoth
were able to survive in the colder climate