The terrain here is tundra, so the rocks and their trends (the general direction
ID: 235478 • Letter: T
Question
The terrain here is tundra, so the rocks and their trends (the general direction in which the rocks are aligned) are visible. This trend, also called foliation, shows the direction in which the rocks are folded. Everything is the same color due to the green tundra plants.
The rocks to the south of the foliation line are of granitic composition and contain isotopes of uranium (U238) that decay to stable isotopes of lead (Pb206). From the amounts of U238 and Pb206 measured in the rocks from this area indicate the 80% of one half life has passed since crystallization. The half- life of U238 is 4.5 billion years (4,500,000,000). How old are these rocks? (Hint: Length of half life x number of half lives passed = time since crystallization)
6109.5015, -76 42.4388 Data SIO, NOAA, U.S. Navy, NGA, GEBCo Image Landsat Coogle earth imagery Date: 12/13/2015 61003126.72" N 76"24'09.77" w elev 791 ft eye alt 131.39 miExplanation / Answer
The rocks to the south of the foliation line are of granitic composition and contain isotopes of uranium (U238) that decay to stable isotopes of lead (Pb206). From the amounts of U238 and Pb206 measured in the rocks from this area indicate the 80% of one half life has passed since crystallization. The half- life of U238 is 4.5 billion years (4,500,000,000). How old are these rocks? (Hint: Length of half life x number of half lives passed = time since crystallization)
The granitic rocks isotopes U238 is 4,500,000,000 years (4.5 billion years)
80% of half life of granitic rocks passed since crystallisation
The age of the rocks = length of half life x number of half lives
= 4,500,000,000 x 80%
=4,500,000,000 x 0.80
=3,600,000,000
=3.6 billion years
So the rocks belong to Archean Eon as Archean Eon spreads over 4.0 to 2.5 billions period.
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