Name______________________________
The Fossil Record
Preserved remains or markings left by organisms that lived in the past are called fossils. Most fossils are found in
sedimentary rocks. Sand and silt eroded from the land are carried by rivers to seas and swamps, where the particles
settle to the bottom. Over millions of years, deposits pile up and compress the older sediments below into rock. Rock
strata, or layers, form when the rates of sedimentation or the types of particles forming the sediments vary over time.
Aquatic organisms can become fossils when they die and are buried in sediments in a way that preserves some of their
structure. Land organisms can become fossils in a similar way, if they are swept into rivers, lakes, swamps, and seas.
Other remains of land dwellers may become fossils after being covered by windblown dust, sand, or volcanic ash.
1. What is sedimentary rock?
2.Why are older fossils generally in deeper rock layers than younger fossils?
3. Describe the different ways that aquatic and land dwelling animals make fossils:
Younger rock strata usually are layered on top of older ones. Thus, the positions of fossils in the rock strata can reveal
their relative age. The fossil record is this chronological collection of life's remains in the rock layers, recorded during
the passage of time.
The fossil record provides evidence of Earth's changing life. The oldest fossil evidence of life consists of chemical traces
in rocks from Greenland that are 3.8 billion years old. Fossils of prokaryotes (Cells with no nucleus) – generally bacteria
and archaea - have been found in rocks of about 3.5 billion years in age. These data fit with the molecular and cellular
evidence that prokaryotes are the oldest form of life. Fossils in younger layers of rock record the evolution of various
groups of eukaryotic organisms (Cells with a nucleus). Fossils of species that became extinct—species that no longer
exist—help paleontologists (scientists who study fossils) reconstruct the past.
1. The evidence shows that the oldest life forms are how old?
2. What other evidence do scientists use to confirm this assertion?
3. Based on the fossil record, which types of organisms came first – prokaryotes or eukaryotes?
Explain your response
4. How does looking at the structures of fossilized organisms help scientists reconstruct the past?
5. What other evidence do scientists use to place these organisms in time?
6. Using the illustration below:
a. Which came first – the organisms in layer D or layer B?
b. The organism on the left of layer B is very similar to the organism to the one in the middle
of layer C. Explain why the fossil evidence may show similar, but not identical remains in
these two layers
7. Go online to this site: http://www.dinofish.com/
a. What is a Coelacanth
b. About how long ago did the first coelacanths live? _____________________
c. .Why is it called a “living fossil”? ______________________________________________
d. When was it “rediscovered”? _____________
8. Go to this site: http://www.guardian.co.uk/science/2009/may/19/fossil-ida-at-a-glance ( or Google “Ida Fossil”)
a. Who is Ida?
b. When did she live
c. How do scientists know she is a primate?
d. How do scientists know she is NOT a lemur?
e. How do they know she was mostly out at night (nocturnal?)
,
f.
.
What did Ida eat?