Geological time

Question 1

Facies

Answer 1

Environment of deposition

Question 2

Why dating isn’t always possible with fossils (biostratigraphy)

Answer 2

Many rocks lack fossils, especially continental ones
Fossil zones may not extend beyond a single continent or region
Few useful fossils before 600Ma i.e. 90% of Earth’s history without fossils
Unconformities are common
Only produces a relative time scale

Question 3

Dating with radioactive elements

Answer 3

Ratio of the unstable parent isotope to daughter isotope gives a date since the half-lives of the parent isotopes are known.
Only closed systems can be dated. Above the closing temperature, daughter isotopes will escape, effectively resetting the clock. Thus, only get the date of the last time the rock cooled through it’s closing temperature.
U-Pb has closing temperature of 700 degrees celsius, which is the temperature of rhyolitic magma. Zircon contains U, and is present in biotite. Biotite is commonin rhyolitic magma. So, this allows for dating when the magma cooled

Question 4

Magnetic polarity reversals

Answer 4

Occurred at the same time everywhere

Question 5

Ooids

Answer 5

Form in high energy environments i.e. shallow, warm, wave-disturbed water
Form from 1 fragment of sediment being rolled around in other sediment