Radioactive carbon dating worksheet
Scientists now know that most elements come in more than one version. When the dry periods ended and the water level rose, the trees drowned, marking the end of the droughts.
Since then, the remains of those trees have been well preserved by the arid climate. To determine how long ago these droughts occurred, Scott is using carbon-14 to date the trees.
Many people assume that rocks are dated at “millions of years” based on radiocarbon (carbon-14) dating. The most well-known of all the radiometric dating methods is radiocarbon dating.
Carbon-14 can yield dates of only “thousands of years” before it all breaks down.
If we know what fraction of the carbon atoms are radioactive, we can also calculate how many radiocarbon atoms are in the lump.
Knowing the number of atoms that decayed in our sample over a month, we can calculate the radiocarbon decay rate.
And as far as we know, it has been forming in the earth’s upper atmosphere since the atmosphere was made back on Day Two of Creation Week (part of the expanse, or firmament, described in Genesis 1:6–8). Cosmic rays from outer space are continually bombarding the upper atmosphere of the earth, producing fast-moving neutrons (subatomic particles carrying no electric charge) (Figure 1a).1 These fast-moving neutrons collide with atoms of nitrogen-14, the most abundant element in the upper atmosphere, converting them into radiocarbon (carbon-14) atoms.
So even we humans are radioactive because of trace amounts of radiocarbon in our bodies.
Meet paleoclimatologist Scott Stine, who uses radiocarbon dating to study changes in climate. What we think of as normal carbon is called carbon-12: six protons plus six neutrons. Several times a year, scientist Scott Stine travels to the shores of Mono Lake, near Yosemite National Park. He's studying the long history of droughts in California, trying to determine how frequently they occur and how long they last.
Find out what it means for an isotope to be radioactive and how the half-life of carbon-14 allows scientists to date organic materials. But about one percent of carbon atoms have an extra neutron, giving them seven. Over the millennia, the water level has risen and fallen, as the area has cycled between wet periods and dry times. During times when the climate was dry, Mono Lake dropped down, exposed the shore lands, and allowed trees and shrubs to grow.
The standard way of expressing the decay rate is called the half-life.5 It’s defined as the time it takes half a given quantity of a radioactive element to decay.
So if we started with 2 million atoms of carbon-14 in our measured quantity of carbon, then the half-life of radiocarbon would be the time it takes for half, or 1 million, of those atoms to decay.