Download fossil - kendricknovak

Welcome to Class
How do we determine the age of
something?
Agenda
• Radioactive Decay Lab
• Fossils Movie
• Fossils Notes
Radioactive Decay Lab
Movie
• Fill out the worksheet as you watch the
movie
• I will be collecting these
FOSSILS
• fossils - trace or remains of organisms
that lived long ago
– discovered in sedimentary rock
• paleontology - scientific study of fossils
• Help find relative and absolute ages of
rocks
Interpreting the Fossil Record
• Fossil Record – provides evidence about
the history of life on Earth
– Shows how organisms have changed over time
• Provide clues to past geologic events,
climates, and the evolution of living things
over time
– see how environmental changes affected living
organisms
Interpreting the Fossil Record
• What do these giant fossilized oysters tell us?
Fossilization
• Dead organisms buried quickly or protected
from decay become fossils
• Generally only the hard parts become fossils
– Rarely an entire organism may be preserved
• Sometimes only a replica of the original
organism remains
– Others provide evidence that life once existed
Mummification
• Mummified remains are found in very dry
places
– most decay causing bacteria cannot survive in
these places
• Some ancient civilizations mummified their
dead
– extracted internal organs and wrapped the
body in strips of cloth
Amber
• Insects get trapped in the sap and are
preserved when the sap hardens
– Hardened tree sap is called amber
• Delicate features (legs/antennae/DNA)
can be preserved
Tar Seeps
• When thick petroleum comes to Earth’s
surface, it forms a tar seep
– covered by water
– Animals become trapped and preserved in the
tar
Freezing
• The low temperatures of frozen soil and
ice can protect and preserve organisms
– Most bacteria cannot survive freezing temps.,
organisms buried in frozen soil or ice do not
decay
Petrification
• Mineral solutions (groundwater) replace
original organic materials
• Some common petrifying minerals are
silica, calcite, and pyrite.
• The substitution often results in the
formation of a nearly perfect mineral
replica of the original organism
Types of Fossils
Using a book, look up types of fossils
Include:
– trace fossils
– imprints
– molds and casts
– Coprolites
– Gastroliths
Types of Fossils
• trace fossil - a fossilized mark that formed by the
movement of an animal on or in soft sediment
• No part of the original organism survives in fossil
form
– fossilized evidence of past animal movement
– provide information about prehistoric life
• A trace fossils in an important clue to the animal’s
appearance and activities.
Imprints
• Carbonized imprints of leaves, stems,
flowers, and fish made in soft mud or clay
• When original organic material partially
decays, it leaves behind a carbon-rich film
– An imprint displays the surface features of
the organism
Molds and Casts
• After a shell is buried, it decays and leaves
an empty space called a mold
– sand or mud fills a mold and hardens forming
a cast
• A cast is a replica of the original organism
Coprolites
• coprolites - fossilized dung or waste
materials from animals
• They can be cut into thin sections and
observed through a microscope.
– See the feeding habits of animals, such as
dinosaurs
Gastroliths
• Some dinosaurs had stones in their
stomachs to help grind their food
– these stones, called gastroliths, survive as
fossils
• Gastroliths are recognized by smooth,
polished surfaces and their close proximity
to dinosaurs remains
Index Fossils
• Index fossil - a fossil used to establish age
of rock layers
– distinct, abundant, widespread
– existed for only a short span of geologic time
• Help determine relative and absolute ages of
rock layers
Index Fossils and Absolute Age
• Scientists can use index fossils to estimate
absolute ages of specific rock layers
• Lived during short spans of geologic time, the
layer where an index fossil was discovered
can be dated accurately
• Scientists can also use index fossils to date
rock layers in separate area