1. Based on fossil evidence, most scientists infer that
(1) life has not changed significantly throughout
Earth’s history
(2) life has evolved from complex to simple forms
(3) many organisms that lived on Earth have become
extinct
(4) mammals developed early in the Precambrian
time period

2. 488 my
-444 my
= 44 my
The geologic cross section below shows the geologic age of two rock layers separated by an unconformity.
The unconformity at the bottom of the Silurian rock layer indicates a gap in the geologic time record. What is the minimum time, in millions of years, shown by the gap?
13 (3) 101
(2) 44 (4) 126

3. Radioactive Decay (Radio dating) Activity
Remember, the thing that informs us about the geologic eras, periods, and epochs is fossils.
Also remember that fossils are dated using radioisotopes
 Radioactive Decay (Radio dating) Activity
Click Me!

4. Fossils of organisms that lived for a short time and were widely scattered are called...
Index Fossils

5. Ask me about my trilobite!
Cryptolithus
from the
Middle Ordovician

6. Same layer! We can use index fossils two ways:
To determine the age of a rock strata.
To correlate rock strata in different locations.
These
are
younger!
This index fossil is 325 million years old.
This strata of rocks is from the mississippian!
Same layer!
These
are
older!

7. What is the name of the index fossil in the shale layer at the bottom of both columns?
(it’s the same in both)
Elliptocephala
Page 8-9

8. During which period was the layer containing Elliptocephala deposited?
(it’s the same in both)
Cambrian
Page 8-9

9. 1) Old Forge 3) Niagara Falls 2) Elmira 4) New York City
In which listed area of New York State may it be possible to find Elliptocephala?
1) Old Forge 3) Niagara Falls
2) Elmira 4) New York City
Page 3

10. Correlating Rock Outcrops
Index fossils found in different locations indicate layers of the same geologic age.

11. Which layers most likely formed at the same time?
Fossils “B” & “D” are from the Ordovician!
The drill-core samples here were taken from two locations 1000 km apart. Rock layers 1 through 8 have been labeled. Some index fossils are shown in the layers.
Which layers most likely formed at the same time?
(1) 1 and 6
(2) 2 and 8 (4) 4 and 7
(3) 3 and 5

12. Which fossil in outcrop I seems to match with fossil D in outcrop II?
Fossil B…so these layers may have been connected!

13. I II
What seems to have happened before the deposition of layer B in column I? U
Erosion!

14. Layer E is missing from Column I.II
What is the evidence for erosion? U
Layer E is missing from Column I.

15. The unconformities represent areas of
The block diagrams show four rock outcrops, A, B, C, and D,
located within 15 kilometers of each other. The rock layers have not been overturned.
The unconformities represent areas of
(1) increased global water demonstrated by melting ice
(2) decreasing stream velocities
(3) lost geological historic evidence
(4) index fossil deposition