Exam 2: ch 25 HW

You have excavated a sample you suspect is about 20,000 years old. What radioactive isotope will you use to date the sample?

Carbon-14

What is half-life?

The time required for half of a radioactive parent isotope to decay to its respective daughter isotope, on average.

What did early researchers hypothesize as the source of energy for making organic molecules?

Electricity from storms and/or UV radiation

What elements did researchers in the 1920s believe the early atmosphere contained?

Nitrogen, ammonia and methane, among others.

If a mass extinction were caused by a single, catastrophic event (such as asteroid impact), what pattern would you expect regarding the dates when formerly common species lost in the extinction are last observed in the fossil record?

Theoretically, these fossils should be observed right up to the extinction event.