Homework 1: Chapter 8

Atom A decays to into atom B with a half-life of 100,000 years. If there are 20,000 atoms of A to begin with (and 0 atoms of B), how long will it take for there to be 2,500 atoms of A?

300,000 years

What is the current best estimate for the age of the Earth?

4.54 billion years

Major difference between an eon and an era

An eon contains multiple eras. While an era corresponds with a set of times and different periods, an eon does not correlate with a particular amount of time.

Which of the following radioactive isotopes is most useful for dating a very young sample (<20,000 years) of wood?

Carbon-14

Major difference between catastrophism and uniformitarianism.

Catastrophism states that the Earth and its form and land were shaped over a short period of time. Uniformitarianism is the fundamental principle of modern geology: that the Earth formed over a long period of time.

Which era was dominated by the dinosaurs?

Mesozoic

What were the major events that occurred in the Paleozoic era?

Plants became abundant and the first vertebrate animals came into existence.

Fossils are most common in which rock types?

Sedimentary

What were the major events that occurred in the Precambrian eon?

The Earth formed during this eon. It is the earliest point of Earth's history, and fossils began to become more and more abundant as this eon went on.

T/F: In the past, there were more atoms of radioactive Uranium.

True

T/F: Rock layers are always older than the layers above them.

True

T/F: The boundaries between eons seem to coincide with major changes in the life forms present on Earth.

True

The largest division of the geologic time scale is the ______

eon

Paleozoic, Mesozoic & Cenozoic are all ______

eras

The Cenozoic Era is known as the Age of ______

mammals