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Name: ________________________________________ Homeroom: ____________
Chapter 8 – Fossils
Important Terms
organism - an individual living thing that carries on the activities of life by means of
organs which have separate functions but are dependent on each other: a living person,
plant, or animal
decay - to become decomposed; rot
extinct - no longer exists
species - A single kind of organism that can reproduce among its own kind; having
some common characteristics or qualities; distinct sort or kind.
Essential Question: How Do Fossils Form?
How Fossils Form
A fossil is any naturally preserved evidence of life. Most often we think of shells
and bones as fossils, but fossils can be much more than that. Fossils can be a
footprint, an impression of a leaf, an animal’s burrow, or even an organism’s waste.
Fossils form in different ways. At times an entire organism can be fossilized.
This could happen if the body dries out, gets _trapped in a bog (swamp), or is frozen.
The remains of woolly mammoths have been found in glacier.
At times insects and small animals are trapped in a flow of tree sap. The sap
then hardens and the insect or small animal is preserved within the sap.
Most often a whole organism is not preserved. When a small animal dies, parts
of the animals are often eaten by a predator and what is not eaten begins to decay. At
times the parts of the hard skeleton that are left get buried in sediment and may slowly
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be changed into rock. What kind of rock would this be? Sedimentary Rock Therefore,
most fossils are found in sedimentary rock, but can also be found in igneous and
metamorphic rock.
Not all fossils are parts of organisms, but only impressions of the organism’s
body. A mold is an impression of an organism that is formed when _sediment hardens
around the organism. If this mold is then filled with sediment and that hardens a cast, or
model, of the first organism is created.
Types of Fossils
Any organism can become a fossil, but certain organisms are more likely to be
fossilized.
Organisms that live in water are more likely to be fossilized than
organisms that live on land. Also organisms with hard parts/tissue, such as shells
and skeletons have a better chance of being fossilized than organisms with only soft
parts.
How Fossil Fuels Form
All living things have energy stored in their cells. Most of the energy we use
today to run machines and to produce electricity comes from the energy stored in the
cells of organisms that lived millions of years ago.
After an organism died, most of its stored energy stayed in the cells of its body
The organisms were then covered in sediment. Over millions of years, the temperature
and pressure caused by the layers of sediment above the organism changed the dead
organisms into fossil fuels. Fossil fuels are energy-rich resources that form from buried
remains of once living organisms.
Three major fossil fuels used today are coal, natural gas, and petroleum.
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Coal is formed when swamp plants die and sink to the bottom of the swamp,
where they decay thanks to the help of bacteria and fungi.
The decayed matter is
buried under sediment, placing more and more pressure on the decayed matter.
Overtime, most of the moisture and oxygen are pressed out, thus leaving a high carbon
concentrate known as coal.
Petroleum and natural gas form mainly from organisms that once lived in the sea.
Protists (organisms with one cell) that live in the ocean capture the energy of the sun
and convert it to stored chemical energy. Once they die they fall to the ocean floor and
are buried by sediment. Over time the pressure and temperature build up and the
remains are changed into petroluem and natural gas. They are collected in pockets
between layers of rock. Oil wells are drilled to recover the petroleum and natural gas
from under the ground.
Where Fossil Fuels Are Found
Petroleum and natural gas are found where oceans once existed. Coal is found
under the sites of ancient swamps. The US has the largest coal deposits in the world,
some are even found right here in PA.
Natural gas burns more cleanly than coal and is often used in place of coal.
Essential Question: What Do Fossils Tell Us About Earth?
Fossils and Earth’s History
Earth is about 4.6 billion years old. No rock on Earth’s surface is as old as the
earth itself because rock is always being formed and destroyed. The oldest rock found
so far is about 3.8 billion years old.
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As you know sedimentary rock most often forms layers, therefore in a group of
untouched rock layers the oldest layer will be at the bottom because it was deposited
first and the youngest layer will be at the top. Scientist often use fossils found in these
rock layers to help determine the age of the rock.
An index fossil is a fossil of an organism that lived during a relatively short time
span. Fossils that are found in many places on Earth and are common make the best
index fossils. Since scientists know when an index fossil organism lived they can then
also tell the age of the rock in which it is found.
Fossils tell more about Earth’s history than the age of certain rock layers. Fossils
can also tell clues about how the Earth’s surface has changed over time. If a fossil of a
sea animal is found at the top of a mountain scientists know that the mountain top was
once very close to water or under water at one time.
Fossils and Continental Drift
The process by which continents move slowing from one position to another is
known as continental drift. The fossils that have been in Antarctica, prove that the
position of Antarctica has changed.
Essential Question: What Do Fossils Tell Us About Life in the
Past?
Ecosystems of the Past
An area in which living things interact with one another and with nonliving things
is known as an ecosystem. Ecosystems change over time. In order to learn about
ecosystems of the past we can study fossils. We know more about ancient saltwater
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and freshwater ecosystems than we do ancient land ecosystems because organisms
living in water have a better chance of being fossilized.
Fossils and Life in the Past
One way for scientist to learn about extinct (species with no living specimens left)
species is through the fossil record. The Age of Fish is early in the history of life, when
many kinds of fish, sharks, and other marine animals roamed the oceans. During the
Age of the Fish there was little life on land.
Scientists are not certain why, but later a mass extinction of ocean animals
occurred. A mass extinction is a period in which a large number of species become
extinct relatively quickly. This was not the only mass extinction in history, from studying
fossils scientist have realized there was a mass extinction of both ocean and land
animals around 250 million years ago. After this mass extinction dinosaurs dominated
the land known as the Age of Reptiles, but dinosaurs also suffered a mass extinction.
Fossils and Changes Through Time
Although some species have become extinct, others have survived by adapting
to changes in their environments. Records of fossils show how organisms slowly
change over time. Not all organisms change as much as others, for instance birds have
changed a great deal, while sharks have changed very little.
For example trilobites were early members of the groups that today includes
insects, spiders, crabs, and horseshoe crabs. Cycads are palm like plants, although
they used to be abundant today only a few kinds still exist.
early type of bird that had some characteristics of dinosaurs.
Archaeopteryx was an