How do scientists use radioactive decay to understand Earth's history?
Radioactive decay does not provide much information on the history of the earth.
The most accurate form of radioactive decay is Carbon 14. However with a half life of approximately only 5700 years Carbon 14 is not very useful in determining the history of the earth. After more than 50,000 years there is so little Carbon 14 left as to be useless for determining ages of material.
All other forms of radioactive dating are based on the decay of igneous materials. As there are only a few examples of fossils being found in igneous materials. This means that radioactive material can not be used to date fossils older than 50,000 years.
Radioactive Uranium 238 can be used to estimate the overall age of the earth. The half life of Uranium is 4.5 Billion years old. By measuring that most of the Uranium 238 found are about 50% decayed it is assumed that the Earth is approximately 4.5 billion years old. This gives the an age for the beginning of the earth.
" I can think of no cases of radioactive decay being used to date fossils. Derek Ager Fossil Frustrations New Scientist vol 100 Nov 10 1983.