Dating Techniques

Bell Ringer: Put the letters in order from earliest event to latest event

Dating Techniques

Bell Ringer: Put the letters in order from earliest event to latest event

•How did you put these pictures in order?•How can scientists determine how old geologic formations are, such as the grand canyon?

Dating Techniques

• Key Concept 1: rocks record geological events and changing life forms of the past

• Key Concept 2: 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 geologic processes that continue today– Erosion– Plate tectonics– Earthquakes– volcanoes

• Key Concept 3: Uniformitarianism - the forces and processes that we observe today have been at work for a very long time

• To understand the past we must first understand the present-day processes and their results

• The surface of the Earth is constantly changing, but not necessarily on the human timescale

Dating Techniques

• Geologists can tell how old certain formations of the earth are based on the age of other things around them

• Key Concept 4: Relative dating tells us the sequence in which events occurred, not exactly how long ago they occurred

Relative Dating

• You can say that layer B is older than layer C, but you cannot say exactly how old either of them are

Youngest: EADC

Oldest: B

• There are 4 laws used in relative dating of geologic formations– Law of superposition– Principle of original horizontality– Principle of cross cutting relationships– Law of Unconformities

Relative Dating

Relative Dating• Key Concept 5: the law 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

Youngest

Oldest

• Key Concept 6: The principle of original horizontality means that layers of sediment are generally deposited in a horizontal pattern

Relative Dating

Relative Dating• Key Concept 7: The

principle of cross-cutting relationships states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected

• Key Concept 8: an unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed

Relative Dating

Relative Dating• Key Concept 9: An angular unconformity

indicates that during the pause in deposition, a period of deformation (folding or tilting) and erosion occurred

• Key Concept 10: To develop a geologic time scale that can be applied to the entire Earth, rocks of similar age in different regions must be matched up. This is called correlation.

Relative Dating

Bell Ringer: How could you more accurately relatively date this formation? What information would you want?

• I need help settling an argument…my dad and I don’t remember how long ago the movie Madagascar came out.

• We are big Phoenix Suns fans so we compared the amount of time to the year certain players were on the Phoenix Suns

Ms. V needs your help

• My dad thinks the movie came out the same year that Shawn Marion, Amar’e Stoudemire, and Kevin Johnson all played together

• I think it was the year that Shawn Marion, Amar’e Stoudemire, and Steve Nash all played together

• How can we settle this argument?

Ms. V needs your help

• What if I gave you something like this?

Ms. V needs your help

Name Years

1970 1975 1980 1985 1990 1995 2000 2005 2010

Paul Westphal

Shawn Marion

Alvan Adams

Connie Hawkins

Tom Chambers

Amar'e Stoudemire

Kevin Johnson

Walter Davis

Sir Chrales Barkely

Steve Nash

• What if we then filled it in with the years these players all played

Ms. V needs your help

Name Years

1970 1975 1980 1985 1990 1995 2000 2005 2010

Paul Westphal

Shawn Marion

Alvan Adams

Connie Hawkins

Tom Chambers

Amar'e Stoudemire

Kevin Johnson

Walter Davis

Sir Chrales Barkely

Steve Nash

• Looking at the table we can determine that the year Shawn Marion, Amar’e Stoudemire, and Steve Nash all played together was 2005

• So…using this “relative dating” technique we can conclude that Madagascar came out in 2005

Ms. V needs your help

• Using the years of the phoenix suns players we were able to determine the relative age of the movie

• The same principle can be applied to geological relative dating

• The location of fossils within geologic formations can also indicate relative age of different layers.

How does the Phoenix Suns relate to earth science?

• The longer a species has lived, the better chance it has of being fossilized and preserved

• Key Concept 11: The type of fossil that is formed is determine by the conditions under which an organism died and how it was buried

Relative Dating - Fossils

• Key Concept 12: A fossil is the remains or traces of an organism preserved from the geologic past

• Key Concept 13: Two conditions are important for preservation: rapid burial and the possession of hard parts

Relative Dating - Fossils

Relative Dating - Fossils

Relative Dating - Fossils

• Key Concept 14: The principle of fossil succession states that fossil organisms succeed one another in a definite and determinable order. Therefore, any time period can be recognized by its fossil content (correlation)

• Just like we determined the age of the movie based on the Suns players (fossil content)

• Index Fossil - a fossil that is only found in a specific time period

• Key Concept 15: Index fossils are widespread geographically, are limited to a short span of geologic time, and occur in large numbers

Relative Dating - Fossils

• Key Concept 16: Fossils can also be used to interpret and describe ancient environments

• If you found this fossil,What type of environmentWould you say it came from?

Relative Dating - Fossils

• What year did these 3 jerseys play on the court together?

Closure

Name Years

1970 1975 1980 1985 1990 1995 2000 2005 2010

Tom Chambers

Amar'e Stoudemire

Kevin Johnson

Walter Davis

Sir Chrales Barkely

• How do we determine the actual age of certain geological features? Or the earth?

• Relative dating only goes so far, we need a way to actually date things

• Key Concept 17: Absolute dating uses radioactive decay to give scientists an actual age of rocks and minerals– Radioactive decay: a nucleus of an unstable atom

loses energy by emitting particles of ionizing radiation

Absolute Dating

• In order to understand absolute dating and radioactive decay you need to understand the structure of the atom

• Key Concept 18: An atom consists of subatomic particles called protons, neutrons, and electrons; Protons and neutrons are found in the nucleus and electrons are found outside the nucleus

Structure of the atom

Structure of the atom

• The basics:– Protons = positively charged– Neutrons = no charge; neutral– Electrons = negatively charged

• Atomic number = number of protons; the identity of the element

• Atomic mass = protons + neutrons

Structure of the atom

• Key Concept 19: When nuclei are unstable, they spontaneously break apart, or decay, in a process called radioactivity

• There are 3 types of radioactive decay:– Alpha emission– Beta emission– Electron capture

Absolute Dating

Absolute Dating• Key Concept 20: A half-life is the amount of time

necessary for one half of the nuclei in a sample to decay to its stable isotope

• Key Concept 21: Each radioactive isotope has been decaying at a constant rate since the formation of the rocks in which it occurs– This is how scientists can determine how old rocks are– This is how the age of the earth was determined

• There are 2 main radioactive isotopes that are used in absolute dating:– Carbon-14 (electron emission)

– Uranium-238

Absolute Dating

• Key Concept 22: An accurate radiometric date can be obtained only if the mineral remained in a closed system during the entire period since its formation

• Key Concept 23: When an organism dies, the amount of carbon-14 gradually decreases as it decays. By comparing the ratio of carbon-14 to carbon-12 in a sample, radio-carbon dates can be determined

Absolute Dating

• NOVA video

Absolute Dating

• Can scientists use the same principles (absolute and/or relative dating) they use to study Earth’s history to study the history of other planets? Why or why not?

Discussion