Geologic Timescale!
 EONS represent the _________________________________
 The ______________________ eon meaning “visible life” is the most recent.
 There is an __________________ of fossils that can document evolutionary trends in
the Earth’s history.
 The phanerozoic eon represents a_________________________________________.
What is termed “____________________” time is divided into 3
eons______________________________________________________________________
This Precambrian time represents _______ of Earth’s history, yet our knowledge of it is
sketchy at best due to the dynamic Earth processes that can seemingly rewrite or erase
history!
 Due to this lack of specific knowledge, we see____________________________.
Fossil Evidence?
 Most Precambrian rocks are _____________________which hinders rock correlation.
 Rocks of such an old age have been ____________________________________over
billions of years.
 It can be compared to a book that is _____________________many chapters!
 We have gained extensive knowledge from _______________________found in
Precambrian rocks.
 Extensive __________________from the middle Precambrian eon (Archean)are
found as a_________________________________. (Fe2O3) The formation of
hematite probably represents a time when there was enough __________to react
with____________________________________________. As the iron was
________________and deposited on the lake and sea bottoms, the formation of iron
rich deposits declined and ________________in the ocean and atmosphere ________.
 Since most of the Earth’s free oxygen is linked to_____________________________,
the formation of extensive Precambrian iron-ore is____________________________.
 There are __________________________in the Precambrian time because there were
no ___________________to form coal swamps and ____________to form petroleum.
Stromatolites!
 Most common fossil from___________________________________.
 Layered mounds or ______________________________________deposited by
algae and bacteria________________________________.
 Any organism found would be microscopic- ________________and later due to
evolution and sexual reproduction,______________________.
 Any life ________________________and therefore did_____________________.