Directions: read 1-3 then start.

1.  Read the purpose & background information below so that this activity will make sense to you.

a.  Gain understanding about how radiometric dating, radioactive decay, and calculations of half life can show the age of rock layers and fossils on Earth.

2.  Go to this Link: http://www.mhhe.com/biosci/genbio/virtual_labs/BL_17/BL_17.html

a.  Trouble with link? Then Google search “Dino Dig McGraw Virtual Lab” click open link and you should see a screen that looks similar to the image right.

3.  Go to the “Procedure” Section

a.  Enter data on the data table.

Background Information:

How does radioactive decay relate to the "Dynamic Earth” and Paleontology (study of fossils) you ask? Well paleontologists not only study fossils, but also chemistry and geologic science as well. Paleontologists dig up fossils out of sedimentary rocks and study all aspects of those surroundings. First know that fossils are formed in a number of different ways; most are formed when a plant or animal dies in a watery environment and is buried under flowing sediments. Over time sediments such as minerals, sand, clay, and crystals builds over the top in strata and hardens into rock.

Scientists are able to find an age of a fossil based on certain known chemical elements in the sediments present around the fossil. If they find those elements they can see the percentage of parent atoms left in the samples to know the half life; if they know how many half lives have passed then they know how much time has passed. Scientists use this process, which is called radiometric dating, to find out the age of crystals and minerals in sedimentary rock and therefore the age fossils inside the rocks.

Here is how it all works: Scientists collect rock samples around, above, and below a fossil out in the field. Once they are back in the lab the scientists use the device called a mass spectrometer to figure out how many half lives the sample has gone through. The mass spectrometer vibrates the sample apart into its atoms so the machine can measure how many of the parent isotopes have converted into daughter isotopes. If the ratio of parent isotopes to daughter isotopes is 50:50 then the sample of rock has gone through one half life.

Half lives vary from element to element, but once scientists know what elements are present nearest to the fossils they can find the isotope percentage to know how long ago the rocks formed and thus how long ago the animal lived and died.

Purpose: To use the process of radiometric dating to learn about the age of a fossil sample.

Prepare to investigate:

1.  Read the background information very carefully.

·  Study the buttons and procedure on this virtual lab to fully understand the steps before beginning simulation.

v  Procedure:

1.  Fill in Data Table 1 and Data Table 2 below as you work.

2.  Use the mass spectrometer in the virtual lab to find the parent isotope type* and the percent of the parent isotope remaining that shows on the virtual computer.

3.  Match the percent of the parent isotope remaining up with the graph to right to find out number of half-lives the sample has gone through.

4.  Using the isotope type from the virtual comp screen, multiply half life value from Data Table 1 by the number of half lives the sample has gone through.

5.  This is how to find the age of the rock layers above and then below the fossils to fill in Data Table 2

Data Table 2 / Age of rock layer above fossil / Age of rock layer below fossil / Inferred age of the fossil / Geologic Time period of fossil (age of fossil) / Type of dinosaur fossil (dinosaur guide book)
Fossil Image
/ 130 million years ago (mya) / 160 mya / 145 mya / Jurassic-Cretaceous / Stego-saurus

6.  Use the geologic time scale button and the dinosaur guide book to fill in the rest of data table 2

* There are 6 isotopes in this simulation which are labeled as isotopes A-F

Data Table 1
Isotopic half life values
Isotope / Time of one half life
A / 220 Million Years
B
C
D
E
F