Samples collected from several of the rocks and sediments in the geologic histor

Question

Samples collected from several of the rocks and sediments in the geologic history above were analyzed to acquire numeric ages. The sample details are . Diorite B has abundant feldspar; using the 40K-40Ar method shows that 92% of the b) parent isotope remains. Conglomerate D contains large gneiss cobbles; amphibole and feldspar collected from the gneiss cobbles is analyzed; using the 87Rb-87Sr method shows that 98% of the parent isotope remains. Granite E has abundant zircon (ZrSiO4); using the 238U-206Pb method shows that 92% of the parent isotope remains The gravel G contains charcoal fragments, using the 14C-14N method shows that 15% of the parent isotope remains Porphyritic andesite H contains zircon; using the 235U-207Pb method shows that the parent isotope remains. · · 88% of . Using the data given for each of the samples, the radioactive decay curve found on the following numeric age of each sample. page and Table 1 from your lab manual fill in the table below to determine the Half-lives Age Sample | % Parent Isotope

Explanation / Answer

Now just look at the geologic Timescale and assign the ages of the rocks with appropriate period or eon

c) Ordovician

d) Cretaceous

e) Proterozoic

f) Cretaceous

g) Mesozoic

h) Quarternary

The data given are not sufficient to answer the other questions.

Sample % Parent Isotope Half-Lives (years) Number of Half-life elapesed Age B 92 1.251×109 0.1 1.251×108 D 98 4.92×1010 0.04 1.968×109 E 92 4.468 ×109 0.1 4.468 ×108 G 15 5730 2.75 1.58×104 H 88 7.038 ×108 0.12 8.4×107

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