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Isn’t it fascinating to think of dinosaurs roaming Earth? Maybe giant nautilus, small trilobites, or huge aquatic dinosaurs such as the plesiosaur swam on land you are now standing on. With its layer upon layer of fossils, walking through Dinosaur National Monument Park will make you think of things like that. When were dinosaurs in this area and when was this dry, arid landscape covered in water?

The Principle of Superposition states: In a series of layered sedimentary rocks the oldest layer is at the bottom and the youngest layer is at the top. ~ R.E.A.L. Science Odyssey Biology 2 Blair Lee, M.S.

2015-08-14 09-53-36 -0600Superposition can be used to determine which occurred first in an area, dinosaurs or organisms swimming in the inland sea, but it cannot be used to determine a date.

The fossils at the monument are found in sedimentary rock, the most likely type of rock to find fossils in. There is a problem using this type of rock for dating. Sedimentary rocks form from bits and pieces of many different rocks that formed at different times in different places. If sedimentary rock were used to learn when events happened the data would show different dates for different pieces of sediment.

2015-08-14 10-47-52 -0600For a more specific answer to the question of when scientists use minerals found in igneous rock layers that formed when volcanoes erupted for radiometric dating. Radiometric dating uses radioactive forms of chemical elements to determine a specific age for rocks and fossils. Most people imagine the igneous layers used for dating to be layers of lava. Layers of lava are used, but are layers of lava that oozed from ancient volcanoes the only igneous layer used for radiometric data? Before answering you should know that when volcanoes erupt they spew lava, ash, and gases. Could ash or gases be used for dating?

2015-08-14 11-03-25 -0600Most of the absolute dating done in the layers at Dinosaur National Monument Park and in areas throughout the world radiometric dating was done on the minerals that spewed out as a part of the volcanic ash. Lava flows along the ground until it cools. This limits the use of lava to limited areas. Ash spews up into the air and is carried huge distances. Eventually the ash falls to the ground and becomes a distinctive igneous layer. Because of the large distances it is carried, the ash is much more useful for radiometric dating.

Here is a photo of the range ash traveled during three successive eruptions that happened at Yellowstone, Wyoming.

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1) Who discovered radioactivity? When was it discovered?

2) Who coined the term radioactivity? She was the first woman to win a very prestigious award. What was the award?

3) She was the first person to win two of these awards. In what area of science were they both awarded?


1406266378Blair Lee M.S. is the the founder of Secular, Eclectic, Academic Homeschoolers. When she’s not busy doing these things, she’s busy writing or working on service projects. She is the author of the critically acclaimed Real Science Odyssey Biology 2 and Chemistry 1, http://www.pandiapress.com/publications/real-science-odyssey/. She is currently working on Astronomy and Earth Science 2 for the series.


(Answers: 1 – Henri Becquerel, 1896 2 – Marie Curie, Nobel Prize 3 – Nuclear Chemistry)