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180 SCIPAD - BIG IDEAS - BOOK 2
THE BASIS OF HEREDITY
Layers and Fossils
The current surface of the Earth has not always been the surface. Older surfaces have been
covered by newer sediments (from volcanic eruptions, floods, etc.) and new surfaces become
exposed by erosion. Almost always, lower layers are older than the layers above them.
The image below shows a cross-section through a small section of the surface of the Earth. Use it
to answer the questions below.
1. Which layer (as indicated by the letters A - H) is the oldest? 
2. Which layer is the youngest? 
3. Scientists have dated layer ‘F’ as being 41 to 33 million years old. It is here that Fossil 2 was
found.
(a) Draw a line from Fossil 2 to layer F.
(b) Fossil 3 was found in a layer below layer F. Does this mean Fossil 3 is older or younger
than Fossil 2? 
(c) Draw a line from Fossil 3 to the layers where it might be found.
4. The 3 whale fossils above are related. Fossil 3 is called Ambulocetus (“walking whale”)
and could walk on land as well as swim. It lived approximately 50 million years ago. It is a
transitional fossil that shows how whales evolved from land-living mammals.
(a) What is the main feature of the skeletons that seems to be getting smaller?

(b) Why do you think this feature is getting smaller? 

(c) Do you think Fossil 1 uses this feature any more? 
(d) Do you think these fossils could be used as evidence for evolution? Justify your
answer. 


A
B
C
D
E
F
G
H
Fossil 1
Fossil 2
Fossil 3
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