Chapter 29
Studying the Past
• Paleontology
• Fossils
• Let’s talk about the
types………
• The study of life that
existed in prehistoric
times
• Preserved remains of
a plant or animal
• Original remains
• Replaced remains
• Original and unchanged
remains of a plant or animal
preserved in a rock –
Amber is an example
(animals caught in sticky
tree sap
• Minerals in groundwater
replace the decaying plant
or animal – like petrified
wood!
• Cast
• A copy of the original
fossil
• Mold
• A depression in a rock
of the original fossil
• Trace fossils
• Impressions such as
footprints, tracks,
burrows or bite marks
Relative Time
• Relative dating
• Strata -
• Placing events in a
sequence in which
they occurred
• Layers of the Earth
Basics…..
• Law of Superposition
• The oldest layers of
rock will be on the
bottom and the
youngest strata or
layers will be on top
• Principle of Cross
Cutting Relations
• The igneous intrusion
that cuts across layers
of rock is always
younger than the
layers it cuts
• Law of Embedded
Fragments
• The fossils or
fragments of rock that
are embedded in a
layer are OLDER because they existed
before
• Correlation
• The matching of rock
layers
• Correlation
• The matching of rock
layers
• Unconformity
• A missing layer in the
rock strata
Absolute Time
• Radioactive Decay
• Half-Life
• Radiocarbon Decay –
Carbon – 14 dating
• The decay of radioactive
isotopes, emitting tiny
particles
• The time it takes ½ of a
radioactive atoms to
decay
• Using the isotope Carbon
14 to date organic
material; half life of c-14
is 5,730 years