Earth’s history is separated into four divisions according to the fossil record:

EonsEras

Periods

Epochs

• The geological time scale reads oldest on the bottom to youngest on the top. Divisions were made by scientists based on fossil records found in rock.

The Mesozoic Era had an inland sea in the North America, this was discovered by the fossils found and dated using Absolute Dating.

Geological Dating Part IIAbsolute Age Dating

Absolute Dating is the actual age of a geological object (rock or fossil).

Coral, Varves, & Tree Growth

Radiometric

Varves

Coral

Tree Growth

Radiometric Dating

• Radiometric Dating is the process by which scientists determine

the ratio of parent nuclei to daughter nuclei within.

• Radiometric Dating gives us the actual date of the fossils or rock. Relative Dating gives us the approximate date.

Comparing Relative to Absolute (Numerical)

Scientists can date age of volcanic ash by dating the fossils and/or rock around it.

Type of Absolute Dating - Radiometric Dating

A radioactive isotope is an element with a different number of neutrons than the original element. Some isotopes slowly decompose by discarding part of the nucleus. The length of time required for half of the isotope’s atoms to decay is the substance’s half-life.

Some radioactive elements with their specific half-life

Each radioactive isotope takes its own particular amount of time to decay. The amount of decay over a period of time (the rate) is a half-life.

• Following death and burial of an organisms wood or bones Carbon C-14 is changed into Nitrogen N-14 during the decay process of the organism.

Fossils are once living things and direct evidence of pastLiving things absorb C-14 during their lifetimes

Fossils can decay C-14 to N-14

• Carbon-14 is a radioactive isotope of Carbon .

• It takes 5,730 years for half of the atoms of Carbon-14 to decay to Nitrogen-14.

• The unstable element (C-14) breaks down to a stable element (N-14) called Radioactive Decay.

• The new element (N-14)

formed after nuclear decay

is called the

daughter element.

What is the fifth radioactive element that forms from uranium-238?

How to date a really old object

• Uranium-238 takes 4,500,000,000 or 4.5 billion years for 50% of the atoms to decay into Lead-206.

• By comparing the ratio of the parent U-238 to the daughter element Pb-206 in the sample, the age of the sample can be determined.

What percentage of parent atoms are remaining after 1 half-life?

What percentage of parent atoms are remaining after 2 half-lives?

Half-Life

• At the end of 1 half-life what is the relationship of daughter to parent material?

• If 2 rocks were found one containing 2 g of A and the other 4 g of A, which rock would be older?

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http://www.math.psu.edu/jech/pictures/GrandCanyon/rocks.jpg

http://earthobservatory.nasa.gov/Study/Paleoclimatology_CloseUp/paleoclimatology_closeup_2.html

www.nps.gov/.../state/tx/1968-7/images/fig26.jpg

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http://www-rohan.sdsu.edu/~rhmiller/geologictime/dikesTexas1.jpg

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http://www.mhhe.com/earthsci/geology/mcconnell/gti/images/utah.JPG

http://www-rohan.sdsu.edu/~rhmiller/geologictime/dikesTexas1.jpg

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http://images.google.com/imgres?imgurl=http://www.winona.edu/geology/MRW/mrwimages/Earth%2520History/metrx_dating.JPG&imgrefurl=http://www.winona.edu/geology/MRW/maps.htm&h=553&w=530&sz=65&hl=en&start=2&tbnid=1fEgWVmmSwDmDM:&tbnh=133&tbnw=127&prev=/images%3Fq%3Dradiometric%2Bdating%2Brocks%26gbv%3D2%26svnum%3D10%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26sa%3DG