Fossils provide evidence about ancient life on Earth. They form when plant or animal remains are rapidly buried and preserved before decay can set in. There are many types of fossils including carbon films, molds, casts, and trace fossils. Paleontologists study fossils to learn about extinct organisms and past environments. Fossils indicate that conditions on Earth have changed dramatically over time, with evidence that seas once covered continents and climates were much warmer or colder in the past.

1. Chapter 16 Lesson 1: Fossils – p564-572 – page 1
Vocabulary
 Fossil (565) – the preserved remains or evidence of ancient living things
 Catastrophism (565) – the idea that conditions and organisms on Earth change in quick, violent events
 Uniformitarianism (566) – a principle that states that geologic processes that occur today are similar to
those that have occurred in the past
 Carbon Film (568) – the fossilized carbon outline of an organism or part of an organism
 Mold (569) – the impression in a rock left by an ancient organism
 Cast (569) – a fossil copy of an organism made when a mold of the organism is filled with sediment of
mineral deposits
 Trace Fossil (569) – the preserved evidence of the activity of an organism
 Paleontologist (570) – scientists who study fossils
 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
Catastrophism
 Many fossils represent plants and animals that are _____________________
 In the past many scientists believed that a single, sudden, catastrophic ________________ killed the
organisms that become fossil
 Catastrophism is the idea that conditions and organisms on Earth change in______________, violent events
o These include large volcanic eruptions and widespread ____________________.
 Scientists eventually __________________ with catastrophism because Earth’s history is full of violent
events
 Most people who supported catastrophism thought that Earth was only a ____________thousand years old

Uniformitarianism
 In the 1700s, James ________________ rejected the idea of catastrophism
 Hutton thought that the processes responsible for changing the
_________________ could also shape Earth’s surface
o For example, he thought that erosion caused by streams could also wear
down ____________________________.
o He realized that these processes would take a long
______________________, and proposed that Earth was much older than a
few thousand years
 Hutton’s ideas were eventually included in a principle called _____________________________________.

2. Chapter 16 Lesson 1: Fossils – p564-572 – page 2
o The principle of uniformitarianism states that geological processes that occur ____________are
similar to those that have occurred in the past
o According to this view, Earth’s surface is constantly being reshaped in a steady, uniform manner
 Today, uniformitarianism is the basis for understanding Earth’s past
 But scientists also know that catastrophic event do ___________________________ occur
o Huge volcanic eruptions and giant meteorite impacts can change Earth’s surface quickly and can be
explained by natural processes
Fossil Formation
 Not all dead organisms become_____________________. More
than likely, you will not become a fossil.
 Fossils form only under _______________________ conditions.
Conditions for Fossil Formation
 Most plants and animals are eaten or ____________when they die,
leaving no trace that they ever lived
o Consider an apple. More than likely an apple will decay into
a _____________lump and be decomposed by bacteria and
insects.
 Some conditions increase the chances that a fossil will form.
1. If the organism has __________parts, such as shells, teeth, or
bones
2. If the organism is _______________quickly after it dies.
o This way the layers of sand and mud slow or stop decay
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
____________.
o Details of microfossils can be seen only under a microscope
Types of Preservation

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 Fossil are preserved in many different ways:
o Preserved Remains
o ___________________________________________
o Mineral Replacement
o ______________________
o Casts
o Trace Fossils
Preserved Remains
 Sometimes the _________________________ remains of organisms are preserved as fossils
 For this to happen, an organism must be completely _________________________ in some material over a
long period of time.
o This would prevent it from being exposed to _________________ or bacteria
o Generally these fossils are less than 10,000 years old. However insects preserved in
____________________ can be millions of years old.
Carbon Films
 Sometimes when an organism is buried, exposure to heat and pressure forces gases and
_________________ out of the organism’s tissues.
 This leaves only the ________________________ behind
 A carbon film is the fossilized carbon outline of an organism or part of an organism
Mineral Replacement
 Replicas, or copies, of organisms can form from _____________________________ in groundwater.
 They fill in the pore spaces or ______________________________ the tissues of dead organisms
 Petrified wood is an example

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Molds
 Sometimes all that remains of an organism is its fossilized
________________ or impression.
 A mold is the _________________________ in a rock left by an ancient
organism
o First, sediment must harden around a buried organism
o As the organism ______________________ over time an
impression of its shape remains in the sediment
o Eventually the sediment turns into ___________________________.
Casts
 Sometimes, after a mold forms, it is filled with more __________________________________
 A cast is a fossil copy of an organism made when a mold of the organism is filled with sediment or mineral
deposits.
Trace Fossils
 Some animals leaves fossilized traces of their _______________________
or activity
 A trace fossil is the preserved evidence of the activity of an organism
 These include:
o ___________________________
o Footprints
o Nest
o Droppings
 These fossils help scientists learn about characteristics and
_____________________ of animals
 They can reveal clues about an organism’s _____________, speed, and
whether they traveled ______________________ or in groups.

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Ancient Environments
 Scientists who study _________________________ are called paleontologists
 Paleontologists use the principle of uniformitarianism to learn about ancient organisms and their
_______________________________.
 They often compare fossils of ancient organisms to organisms living ___________________________
o For example, trilobite fossil and ______________________________ crabs look alike
o Horseshoe crabs today live in shallow water on the ocean floor
o Partly because trilobite fossils look so much like horseshoe crabs, paleontologists
__________________ that trilobites also lived in shallow ocean waters
Shallow Seas
 Today, Earth’s continents are mostly above ______________________________________.
 But, sea level has ________________________ , flooding Earth’s continents, many times in the past
 For example, a shallow ocean covered much of North America ___________________ million years ago.
 Fossils of organisms that lived in that shallow ocean help scientists reconstruct what the
_________________________ looked like at that time.
Past Climates
 Evidence indicates that Earth's present-day climate is ____________________________.
 Fossils show that Earth's climate has warmed and ___________________________ many times in the past
 ______________________ 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

6. Chapter 16 Lesson 1: Fossils – p564-572 – page 6
was very warm 100 million years ago
o Tropical forests and _____________________________ covered much of the land
o Millions of year later, the swamps and forests were gone, but coarse _______________________
grew in their place
o Huge sheets of ice called __________________________spread over parts of N. America, Europe,
and Asia.
o Fossils suggest that some species that lived during this time, such as the woolly mammoth were able
to survive in the colder climate