Transcript Fossils

Fossils
A Trip Through Geologic Time
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Fossils are preserved
remains or traces of living
things.
Most fossils form from
animals and plants that lived
near quiet water, such as
swamps, lakes, or shallow
seas, where sediments build.
The organism dies and the
remains are buried by
sediments.
The sediments slowly
harden into rock and
preserve the shape of the
organisms.
Fossils
Fossils
Fossils are usually found
in sedimentary rocks.
 When an organism
dies, its soft parts often
decay quickly or are
eaten by animals
leaving only the hard
parts to fossilize.
 Ex. bones, shells, teeth, seeds, or woody stems.
 For a fossil to form, the remains or traces of an
organism must be protected from decay.
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Kinds of Fossils
Petrified Fossils: fossils
in which minerals replace
all or part of the organism.
Ex: petrified wood
 When the object is buried
by sediment, water rich in
minerals seeps into the
cells. After the water
evaporates, hardened
minerals are left behind.
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Kinds of Fossils
cast
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mold
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A mold and cast of a trilobite.
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Molds and Casts are the most
common type of fossil.
A mold is a hollow area in sediment in
the shape of an organism or part of an
organism.
It forms when the hard part of the
organism is buried in sediment.
Water carrying dissolved minerals
and sediment may seep into the
empty space.
If the water deposits the minerals and
sediment there, the result is a cast.
A cast is a copy of the shape of an
organism.
Molds and Casts are opposites.
Kinds of Fossils
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Carbon Films: an extremely thin coating of carbon
on rock that forms when materials that make up an
organism become gases and escape leaving only
carbon behind.
A thin layer of carbon remains preserving the
delicate parts of leaves and insects.
Trace Fossils provide evidence of the
activities of ancient organisms. Ex:
footprints, animal trails, or animal
burrows.
Fossilized Footprints: mud and sand
that the animal stepped on was buried
by layers of sediment. The sediment
became rock, preserving the footprints.
Trace Fossils provide evidence of
animals size and behavior.
Trace Fossils
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Traces that reflect animal
behavior.
A = crawling traces
B = resting traces
C = dwelling traces
D = grazing traces
E = feeding traces
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Coprolite is fossilized feces
(animal waste).
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Coprolites record the diet,
feeding behavior, and habitat
of prehistoric animals.
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If the coprolite consists of partially digested plant
material (leaves, seeds, bark, roots), the animal was
probably an herbivore.
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If the coprolite contains bits of animal material
(crushed bits of bones, sinew, claws), the animal was
a carnivore.
Kinds of Fossils
Preserved Remains are formed
when an organism is preserved
with little or no change.
 For example when organisms
become preserved in tar, amber
(tree sap), or are frozen.
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Beetle in Tar Sand
Insect in Amber
Frozen Baby Mammoth
Amber
 Insects
get caught in tree sap and die.
 More sap is added on.
 The sap hardens, preserving the insect inside.
Petrifaction
Process in which minerals replace an organism’s
tissues.
 Permineralization: pore space (bone or wood) is
filled with minerals.
 Replacement: the organism’s tissues are completely
replaced by minerals.
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Asphalt
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Pools of thick, sticky asphalt trap and preserve organisms.
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La Brea Tar Pits – Pit 91
Freezing
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Cold temperatures slow decay.
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Organisms that freeze are preserved for long periods
of time.
Fossil, or Not?
Why Study Fossils?
Scientists study fossils
to learn what past life
forms were like.
 Paleontologists
classify organisms in
the order in which they
lived.
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All the information
scientists have
gathered is called the
fossil record.
Fossil Record
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The fossil record provides
evidence about the history
of life on Earth.
The fossil record also
shows how different groups
of organisms have
changed over time.
It also provides evidence to
support the theory of
evolution.
Remember!
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A scientific theory is a
well-tested concept that
explains a wide range of
observations.
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The fossil record shows
that millions of types of
organisms have evolved.
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However, many others became extinct.
Using Fossils to Date Rocks!
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Scientists use index
fossils to match rock
layers.
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An index fossil must
be widely distributed
and represent a type of
organism that existed
only briefly.
They are useful because they tell the relative ages of
the rock layers they are found in.
The Trilobite
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One example of an index fossil
is a trilobite.
Trilobites were a group of hardshelled animals whose bodies
had three distinct parts.
They evolved in shallow seas
more than 500 million years
ago.
Geologic Time Scale
• Since the history of the
Earth is so long (4.6
billion years), geologists
break the time period up
into smaller pieces.
• The largest divisions are
eons:
 Hadean Eon
 Archean Eon
 Proterozoic Eon
 Phanerozoic Eon
Eons are divided into
Eras.
 Eras are divided into
Periods.
 Periods are divided into
Epochs.
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The boundaries
between geologic time
intervals represent
when visible changes
took place on the Earth.
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The Paleozoic Era (meaning "ancient life") lasted from 600
million years ago until 248 million years ago.
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During the Paleozoic Era, many life
forms still present today first
appeared, such as jellyfish, coral,
insects, spiders, fish, amphibians,
reptiles and ferns.
There were few land organisms.
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It was the first era well represented
by fossils.
 By the end of the era, amphibians
and reptiles lived on the land and
insects were abundant.
It came to an end with the largest mass extinction in Earth’s history.
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Some scientists believe it was causes by ocean changes.
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The Mesozoic Era (meaning "middle life") lasted from 248
million years ago until 66 million years ago.
During the Mesozoic Era, many of
the more complex life forms first
evolved, including mammals,
birds, and flowering plants.
 However, the Mesozoic is best
known for the presence of its
largest and most famous animals:
the dinosaurs!
 It is known as the Age of
Reptiles.
 It’s believed that birds evolved
from a type of dinosaur.
Along with the dinosaurs, about 20% of all species on Earth became
extinct at the end of the Mesozoic Era.
The cause may have been global climate change.
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The Cenozoic Era started 66 million years ago and continues
today.
 This era is known as the
Age of Mammals.
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In the Mesozoic era,
mammals had to compete
with dinosaurs and other
animals for food and shelter.
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After the mass extinction at
the end of the Mesozoic,
mammals flourished.
Their unique characteristics may have helped them adapt and
survive the environmental changes that caused the extinction of
the dinosaurs.
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The Cenozoic is divided into
several epochs: Paleocene,
Eocene, Oligocene,
Miocene, Pliocene,
Pleistocene, and Holocene.
In particular, the Miocene
Epoch lasted from 24 million
years ago until 5 million
years ago.