Key Words
Fossil: the preserved remains or traces of living things
Paleontologist a scientist who studies fossils to learn about organisms that
lived long ago.
sedimentary rock: the type of rock that is made of hardened sediment
Petrified fossil: a fossil in which minerals replace all or part of an organism
Mold: a fossil formed when an organism buried in sediment dissolves, leaving
a hollow area.
Cast: a fossil that is a copy of an organisms shape, formed when minerals
seep into a mold.
Carbon film: a type of fossil consisting of an extremely thing coating of carbon
on rock.
Trace fossil: a type of fossil that provided evidence of the activities of ancient
organisms
Scientific theory: a well-tested concept that explains a wide range of
observation
Evolution: the process by which all the different kinds of living things have
changed over time.
Extinct: describes a type of organism that no longer exists anywhere on Earth
Key Words
Relative age: the age of a rock compared of the ages of rock layers
Absolute age: the age of a rock given as the number of years since the rock
formed.
Law of superposition: the geologic principle that states that in horizontal
layers of sedimentary rock, each layer is older than the layer above it and
younger than the layer below it.
Unconformity: a place where an old, eroded rock surface is in contact with a
newer rock layer.
Intrusion: an igneous rock layer formed when magma hardens beneath
Earth’s surface.
Extrusion: an igneous rock layer formed when lava flows onto Earth’s surface
and hardens.
Index fossil: fossils of widely distributed organisms that lived during only one
short period.
Radioactive decay: the breakdown of a radioactive element, releasing
particles and energy
Essential Question
• How do scientist know that different kinds of
plants and animals lived in Earth’s past?
Journal your answer
http://www.youtube.com/watch?v=zPCZdhurY
xg
Evidence of Ancient Life
Fossils are the preserved
remains or traces of living
things.
Fossils provide evidence of
how life has changed over
time.
Fossils also help scientists
infer how Earth’s surface has
changed.
Fossils are clues to what past
environments were like
Most fossils form when living things die and are
buried by sediments. The sediments slowly
harden into rock and preserve the shapes of the
organisms.
Water fossilization
Land fossilization
http://www.youtube.co
m/watch?v=SEDfRy6DQ
ns
http://www.youtube.com/watch?v=G4jM2t3N
HPA
Sedimentary Rock
This is a rock type that is made of hardened sediment. Most fossils form
from animals or plants that once lived in or near quiet water such as
swamps, lakes, or shallow seas where sediments build up.
When an organism dies, its soft parts often decay quickly or are eaten by
animals. Thus, generally only hard parts leave fossils. These hard parts
include bones, shells, teeth, seeds and woody stems. It is rare for the
soft parts of an organism to become a fossil.
Petrified fossils
• A fossil may form when the remains of
an organism become petrified.
• The term petrified means “turning into
stone”.
• Petrified fossils are fossils in which
minerals replace all or part of an
organism.
Petrified Wood:
formed after sediment covered
the wood. Then water rich in dissolved
minerals seeped into spaces in the plant’s
cells. Over time, the water evaporated,
leaving the hardened minerals behind.
Some of the wood remains but he
minerals have hardened and preserved it.
Molds and Casts
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Most common fossils are molds and casts
Copy the shape of ancient organisms
Mold is hollow area in sediment in the shape of an organism or part of an
organism
Forms when the hard part of the organism, such as a shell, is buried in
sediment.
Water carries dissolved minerals and sediment into the empty space of the
mold.
If the water deposits the minerals and sediment a cast is formed.
A copy of the shape of an organism.
Cast is the opposite of a mold
Watch the animations then take the quizzes
•
http://www.abc.net.au/beasts/fossilfun/makingfossils/default.htm
•
http://glencoe.mcgrawhill.com/sites/dl/free/0078778026/164155/00076703.html
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http://studyjams.scholastic.com/studyjams/jams/science/rocks-mineralslandforms/fossils.htm
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Trace fossils
• Most types of fossils preserve the shapes of ancient
animals and plants.
• Trace fossils provide evidence of the activities of
ancient organisms.
• A fossilized footprint print is one example of a trace
fossil
• Trace fossils provide clues about an animals size and
behavior. How fast could the animal move. Did it walk
on two or four legs? Did it live alone or in a pack.
• http://www.pbslearningmedia.org/asset/ess05_int_fos
silintro/
Relative age of rocks and Index Fossils
•
http://www.youtube.com/watch?v=ydDuT5V9zwM
http://www.mhhe.com/biosci/genbio/virtual_la
bs_2K8/labs/BL_11/index.html