Question

Question #7a434

Answer 1

D a constant half life.

Explanation:

A. radioactive uranium is fatal to organic life. it breaks down into radon a radioactive gas which when inhaled creates cancer. The gamma radiation given off by the breakdown of uranium is harmful to living things damaging the DNA ( The atomic bomb dropped on Hiroshima was made of Uranium) A is wrong.

B. Yellow cake uranium is very soluble in water, Uranium is very susceptible to weather and erosion causing potentially huge errors in the dates determined by the half life of uranium as large amounts may have been weathered or eroded away. B is wrong.

C. Uranium does not commonly occur in sedimentary layers. Uranium 238 Lead dating like all forms of radioactive dating beside Carbon 14 can only be used to date igneous rocks. ( Carbon 14 can not be used to date sedimentary rocks either as its short half-life of approximately 5700 years make dating anything more than 57000 years inaccurate and useless { this is 10 half-lives `1/2^10` }) C is wrong.

D.. the half-life of Uranium is constant and has been precisely measured and calibrated. However given the long half-life of Uranium 238 4.5 billion years. it can not be accurately used for shorter time periods. An igneous rock with only 1/8 of the original pure rock of uranium be over 75,000,000 years old. This is assuming that the original rock was 100% uranium and has experienced no weathering or erosion over the 75 million years being measured. ( most likely false assumptions)

D. is the best answer Though the dates determined by Uranium 238 can not be considered to be accurate the constant half life of Uranium 238 may give a good approximation for longer time periods. ( radioactive dating the lava of Hawaii volcanos due to recent eruptions have yielded dates of more than 1.2 million years)