Download Check for Understanding- Objective 1 ANSWER KEY

Check for Understanding- Objective 1
Geologic History of the Earth
1. What is the theory of plate tectonics?
2. Rank the following divisions of geologic time from largest amount of time to smallest amount
of time:
a. Epochs
b. Periods
c. Eras
d. Eons (largest unit of time!)
e. Year
f. Century
3. Rank the following eras from largest amount of time to smallest amount of time.
a. Paleozoic Era
b. Precambrian Era
c. Mesozoic Era
d. Cenozoic Era
4. Estimate the approximate time in the history of Earth when each of the following events
occurred:
a. Age of the Earth: ____
b. First bacteria appear on Earth: _____
c. First photosynthetic plants appear on Earth: ______
d. First land animals appear on Earth: ______
e. Modern Humans Appear: ______
5. Describe the composition of early Earth’s atmosphere.
6. What is extinction? How has extinction impacted life on Earth?
Check for Understanding- Objective 1 ANSWER KEY
Geologic History of the Earth
1. What is the theory of plate tectonics?
Plate tectonics is a theory that describes the large-scale movements of Earth’s crust. This theory
states that Earth’s crust is made of over a dozen pieces of solid rock of varying sizes. Where these
plates touch is known as a plate boundary and these boundaries help shape the physical appearance
of Earth over time.
2. Rank the following divisions of geologic time from largest amount of time to smallest amount
of time:
Largest to Smallest: Eon, Era, Period, Epoch, Century, Year
3. Rank the following eras from largest amount of time to smallest amount of time.
a. Paleozoic Era
b. Precambrian Era
c. Mesozoic Era
d. Cenozoic Era
Largest to Smallest: Precambrian, Paleozoic, Mesozoic, Cenozoic
4. Estimate the approximate time in the history of Earth when each of the following events
occurred:
a. Age of the Earth: 4.5 billion years old
b. First bacteria appear on Earth: 3.5 billion years ago
c. First photosynthetic plants appear on Earth: 2.5 billion years ago
d. First land animals appear on Earth: 475 million years ago
e. Modern Humans appear: 200,000 years ago
5. Describe the composition of early Earth’s atmosphere.
Today, Earth’s atmosphere is composed of mostly nitrogen and oxygen. The atmosphere of early
Earth was primarily composed of helium and hydrogen.
6. What is extinction? How has extinction impacted life on Earth?
Extinction is the disappearance of an entire species. Over 99% of all the species that ever lived on
Earth is now extinct.