Transcript the geologic time scale

GEOLOGIC
TIME SCALE
LOOK AT THIS TIME
SCALE.
TELL ME 3 THINGS
ABOUT WHAT YOU
SEE.
TELL ME ONE THING
YOU ALREADY KNOW
AND ONE THING
YOU WANT TO
KNOW.
Rocks Record Earth History
 Rocks record geological events and changing
life forms of the past.
 We have learned that Earth is much older than
anyone had previously imagined and that its
surface and interior have been changed by the
same geological processes that continue
today.
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They may contain fossils
Older rocks are usually below younger ones.
Some rocks contain radioactive isotopes.
Based on their interpretations of the rock
record, geologists have divided Earth’s 4.6billion-year history into units that represent
specific amounts of time. Taken together,
these time spans make up the geologic time
scale.
 Interpreting Environments
•
Fossils can be used to interpret and describe
ancient environments.
graptolites, gingko, trilobite
How they form
 Answer these questions during the video:
1- People who study fossils are called ___________________
2- Fossils are at least ________ years old.
3- Trace fossils could be _________, _________ or _________________
4- A resin fossil is made when small creatures get trapped in tree
_____.
5- Most fossils form when a dinosaur falls in ___________ and is
covered by ___________.
Fossil formation
The principle of
superposition states
that in an
undeformed
sequence of
sedimentary rocks,
each bed is older
than the one above it
and younger than the
one below it.
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Relative dating- rock Y is younger than rock Z
because Y is above Z. Similar to saying that I
am older than you, but younger than your
grandparents.
Absolute dating – rock Y is 22,000 years old
and rock Z is 1.5 million years old.
Principle of superposition uses relative dating
and radiometric dating uses absolute dating.
Radiometric Dating
 Radiometric dating is the procedure of
calculating the absolute ages of rocks and
minerals that contain radioactive isotopes.
 This is the method used to date the oldest
rocks.
 Each radioactive isotope has been decaying
at a constant rate since the formation of the
rocks in which it occurs.
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It is the time it takes for half of a substance to
decay (or change) into a new substance because
the original substance is radioactive which means
it is unstable. In order for the substance to
become stable, it may release alpha, beta or
gamma radiation. The release of these particles
may change the identity and mass of the original
substance.
For example, as uranium-238 decays, it releases
alpha and beta radiation to eventually become
lead-206. New element, new mass. Scientists
compare the amount of U-238 to Pb-206 to
determine the age of the rock.
Dating with Carbon-14
 Radiocarbon dating is the method for
determining age by comparing the amount of
carbon-14 to the amount of carbon-12 in a
sample.
 When an organism dies, the amount of
carbon-14 it contains gradually decreases as
it decays. By comparing the ratio of carbon14 to carbon-12 in a sample, radiocarbon
dates can be determined.
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Used to date the ages
of once living things
(all living things
contain carbon).
Can only date
substances up to
60,000 years
because the half-life
of C-14 is pretty
fast.
Found in sedimentary
rocks.
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Used to date the
oldest rocks.
Has a very long halflife (4.5 by).
Dates igneous rocks
(those formed from
cooled magma/lava).
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Geologize
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The half-life of potassium is 1.3 billion years.
A rock contains 100 grams of potassium and
was formed 3.9 bya.
a) How many half lives have passed?
3 half lives
b) How many grams of potassium remain?
12.5% grams
c) What percent of the original potassium is
now in the rock?
12.5%