Name: ___________________________________________ Date: ___________ Period: _________
Reading Guide 13.1 Precambrian Time: Vast and Puzzling
I. Precambrian History
A. The Precambrian encompasses Earth’s history from ______________________________ years ago to the
start of the ______________________ period, over ____________________________ years later.
B. Most Precambrian rocks lack ___________________, which makes correlating rock layers difficult.
C. Precambrian Rocks
1. The lack of Precambrian rocks at the surface of the Earth illustrates the law of
______________________________________.
2. Areas where Precambrian rocks dominate the surface are called _________________ because of their
shape.
3. Most of our knowledge about Precambrian rocks comes from the __________ mined from the shields,
such as ________________________________________________________________________________
______________________________________________________________________________________.
D. Earth’s Atmosphere Evolves
1. The air you breathe is a stable mixture of ________________________, ________________________, a
small amount of ___________________, and trace gases like _____________________________________
and ____________________________________.
2. Earth’s original atmosphere was made of gases similar to those released in _________________________
___________________________________ today--______________________________, ______________
______________________, _______________________________, and several trace gases, but no
__________________________.
3. The cycle of _______________ led to the cooling of Earth’s surface and the reduction of the amount of
water vapor and ____________________________________________ because it became dissolved in the
water.
4. The first life forms on Earth did not need ________________________. Later, primitive organisms
evolved that used _________________________________ and released _______________________.
a. These organisms were primarily ___________________________________________.
b. They dramatically altered Earth’s atmosphere by using ___________________________________ and
releasing ________________________.
5. Oxygen began to accumulate in the atmosphere about ______________________________________
years ago, after the first free oxygen has reacted with all the available _____________ to form rust.
E. Precambrian Fossils
1. The most common Precambrian fossils are __________________________________, distinctively
layered mounds or columns of _________________________________________________ that are not the
remains of organisms, but material deposited by _________________.
2. Stromatolites did not become common until the middle of the Precambrian, about
_________________________ years ago, although remains of _________________________ and
_________________________________________ have been discovered, extending the record of life back
beyond ________________________________ years.
3. Precambrian fossils are usually preserved in a hard, dense chemical sedimentary rock called
________________.
4. Other common Precambrian fossils are primitive organisms called _____________________________,
_______________ fossils that give indirect evidence of an organism’s activities, and microscopic
organisms.
Section 13.1 Assessment p. 368 #1-7
1.) ________________________________________________________
2.) _______________________________________________________________________________________
_______________________________________________________________________________________
3.) _______________________________________________________________________________________
4.) _______________________________________________________________________________________
_______________________________________________________________________________________
5.) _______________________________________________________________________________________
_______________________________________________________________________________________
6.) _______________________________________________________________________________________
_______________________________________________________________________________________
7.) _______________________________________________________________________________________
_______________________________________________________________________________________