Download Refer to the chart of Geologic Time in Connecticut to help answer

Refer to the chart of Geologic Time in Connecticut to help answer the questions.
Pretend that each table represents a rock with the determined ratio of U-235 to Pb-207.
1. The Iapetos Ocean was an ocean that existed before Pangea formed. Which “Rock Table” would
likely represent rocks formed by the early phase of Iapetan rifting? The rock at Table 1, which
represents rock that is one half-life old, is 704,000,000 years old. According to the chart of
Geologic Time in Connecticut, the Early phase of Iapetan rifting occurred between 700-750
million years ago. The basalt that formed during the Neoproterozoic Period would be about
704,000,000 years old.
2. Which “Rock Table” might represent the oldest basement rocks in NW Connecticut? The oldest
basement rock (rock closest to the lithosphere) in NW Connecticut are described on the chart of
Geologic Time in Connecticut in the Mesoproterozoic Period, between 1 billion,100 million years
ago and 1 billion, 600 million years ago. Table 2 rocks are about 1 billion, 408 million years old.
3. What type of rocks would you be likely to date using radiometric technology, igneous or
sedimentary?
What is your reasoning? You could refer to the worksheet with the three laws of relative dating
for a hint. Formations of igneous rock come from one source and one time. Sedimentary rocks
are made from bits and pieces from various places.
4. How many Pb-207 atoms are there for every U-235 atom at Table 4? Show your work! For every
U-235 atom at Table 4, there are 15 Pb-207 atoms. At Table 4, there were 8 U-235 atoms, and
120 Pb -207 atoms. 8 divided by 8 = 1; 120 divided by 8 = 15.
The Challenge: If the ratio of U-235 : Pb-207 is 1 : 15, how old is the rock?