Download Radiometric Dating

Dating & Fossils
PP 282-284 AND 302-303
Geologic Dating
Relative (qualitative): Determines if
one thing is younger or older than
another.
◦ Ex: Law of Superposition, use of index
fossils, correlation of rock layers.
Absolute (quantitative): Determines
how many years old something is.
◦ Ex: Radiometric Dating
Absolute Dating
◦Radiometric Dating =
calculating the age of an
object by measuring
proportions of isotopes
Relative Dating
Law of Superposition
◦Younger rocks are on top, older rocks are on
bottom.
◦Lower layers must be in place before younger
rocks can be deposited on top of them
FOSSILS
Fossils are the preserved
remains or traces of living
things.
◦ Fossils provide evidence of how
life has changed over time.
How are Fossils Formed?
Fossils form when living things
die and are buried by
sediments. The sediments
slowly harden into rock and
preserve the shapes of the
organisms
Types of Fossils
Permineralization- minerals are
deposited around or replace the
hard structure
Casts- flowing water removes all
of original bones, leaving
impression in sediment, then
minerals fill in the mold
Trace fossils- record activity of
organisms such as burrows,
imprints of leaves, and footprints
Amber- organisms trapped in
tree resin that hardens
Preserved remains- form when
entire organism becomes
encased in material such as ice,
volcanic ash, or immersed in
bogs.
The Fossil Record
Fossils also help scientists infer how Earth’s
surface has changed.
Shows that fossils occur in a particular pattern.
◦ Older rocks contain fossils of simpler
organisms.
◦ Younger rocks contain fossils of more complex
organisms.
o Provides evidence about the history of life
on Earth.
o Fossils are clues to what past
environments were like.
o Shows that different groups of organisms
have changed over time.
Geologic Time Scale
A system of chronological dating that relates
geologic land forms (strata) to time.
Shows sequence of major evolutionary events.
Geologists have divided Earth’s history into time
units based on the fossil record