In the last few years improvements in technology have allowed geologists to date single grains of some minerals in rocks. A geologist separates 5 grains of the mineral zircon, which can be dated by the Uranium-lead method, and the crystal retains parent and daughter through weathering, erosion, and deposition. Thus, dating each mineral grain only gives the age of the source rock that was eroded, to produce that sand, from which the zircon grain is derived. The 5 grains yield ages of 160, 110, 2020, 66, and 162 million years. What do these ages tell you about the age of the sedimentary strata?
◦ They are Precambrian rocks, older than 2020 million years.
◦ They are younger than 66 million years.
◦ They are between 160 and 162 million years.
◦ There are no age constraints from this data; sedimentary rocks cannot be dated by geochronology.
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Children can fast map the meanings of words in a single exposure.
Toddler: 1–3 years.
Extinction and extirpation per years
Testcross of a single character
Earth 200 Million Years Ago