Name: Geologic History Discussion Questions
Precambrian Events 4.6 bya - 540 mya
A. How were conditions on early Earth different
from Earth today? What challenges would
organisms of today face if there were
transported back to early Earth?
Conditions to consider: atmospheric gases,
temperatures, land masses, oceans, and
volcanism
B.
How did the arrival of photosynthesizing bacteria change physical conditions on Earth? Discuss
more than one result.
A. Why were organisms restricted to living in oceans during Precambrian time? What challenge
would life forms face on land at this time?
B. How might photosynthesizing bacteria trigger the global ice age known as Snowball Earth?
C.
How did Snowball Earth affect life forms on the planet?
Paleozoic Era: 540 – 245 mya
A.
The Paleozoic started with an ice-covered planet. What pulled Earth out of Snowball Earth? Be
specific.
B.
For most of the Paleozoic, life existed in shallow oceans. The major landmass, Rhodinia, started
remained a lifeless barren rock for a long time. This is because there was no protection from
ultraviolet radiation from the sun (UV causes mutations to DNA and ultimately kills cells).
Today, organisms are partially protected from UV radiation by ozone – a molecule of oxygen in
the upper atmosphere. The development of an ozone layer was an important step in allowing
life to evolve on land.
How did photosynthesizing organisms helped to build a ozone layer?
C.
The Paleozoic starts out with the “Cambrian Explosion”. What does the “Cambrian Explosion”
refer to?
D. The Paleozoic closes with a mass extinction called “The Great Dying” at the end of the Permian.
Pick one of the links below to read. Summarize the potential causes of the Permian extinction
(in bullet form)
http://dsc.discovery.com/dinosaurs/permian-extinction.html
http://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction/
http://nai.nasa.gov/news_stories/news_detail.cfm?ID=286
Mesozoic Era: 245 – 65 mya
A.
Describe the climate of Earth during Mesozoic times. What was responsible for this difference?
B.
How did an asteroid impact cause a mass extinction of the dinosaurs? Discuss the changes in
physical environment that would be associated with a meteorite impact.
http://www.enchantedlearning.com/subjects/dinosaurs/extinction/Asteroid.html
Cenozoic Era: 65 mya – Present
A.
Contrast the climate in the Mesozoic to that of the Cenozoic.
Trends and Big Idea questions
 Earth’s history is “punctuated” with mass extinctions. Explain what this statement means. Be
sure to give an example.
 When it comes to climate, environment, and life forms, why might it be difficult for scientists to
define what Earth’s “NORMAL” is? Based on events in Earth’s history, predict whether is likely
that Earth will remain the way it is today (in terms of climate, environment, and life forms).
 Volcanoes are incredibly important in maintaining Earth’s climate balance. They also have
disrupted life at various points in Earth’s history.
 Give an example of an instance where volcanoes helped to return Earth to conditions
favorable to life.
 Give an example of an instance where volcanoes have triggered mass extinction.