1. Evidence of Evolution
Chapter 12

2. Geologic
Time Scale

4. Fossil Record
• Evidence of organisms
from long ago
• Formed in many ways
• Layers of earth
show relative age
of fossils

5. Formation of Fossils
A compression fossil is a fossil preserved in
sedimentary rock that has undergone physical
compression.

6. Formation of Fossils
Petrification is the
process by which
organic material is
converted into stone
through the
replacement of the
original material and
the filling of the
original pore spaces
with minerals.

7. Formation of Fossils
Compression fossils, such as those of
fossil ferns, are the result of chemical
reduction of the complex organic
molecules composing the organism's
tissues. In this case the fossil consists
of original material, albeit in a
geochemically altered state. Often
what remains is a carbonaceous film
known as a phytoleim, in which case
the fossil is known as a compression.
Often, however, the phytoleim is lost
and all that remains is an impression
of the organism in the rock—an
impression fossil.

8. Formation of Fossils
Molds and Casts
In some cases, the original bone
or shell dissolves away, leaving
behind an empty space in the
shape of the shell or bone.
This depression is called a mold.
Later, the space may be filled
with other sediments to form a
matching cast in the shape of
the original organism. Many
mollusks (bivalves, snails, and
squid) are commonly found as
molds and casts because their
shells dissolve easily.

9. Formation of Fossils
Oozing tree sap can trap insects. When the sap (or resin) fossilizes,
it becomes amber.

10. Dating Fossils
• Relative Dating—based on where in layers of
rock it is.
– Does NOT assign an exact age
• Absolute Dating—test fossil or sediment
around it to get a date range
– Radiometric Dating—uses radioactive isotopes
• Based on half life—amount of time it takes for half the
substance to decay
• Ex. Carbon-14

11. Carbon 14 Dating
•Carbon dating is used to date archaeological samples to the relative dates that the
sample was from.
•The half-life of Carbon-14 is approximately 5,700 years, and as long as there is traces
of Carbon-14 in something, you can age it accurately.
•After an animal or other living
thing dies, Carbon-14 slowly
forms back into Nitrogen
and returns back into the
atmosphere, but regular
Carbon-12 does not decay
so if all the Carbon-14 decays,
then you can not age that
material

12. Biogeography
Darwin noticed:
– The further away he got from home, the more different
the species were from those he recognized. In particular,
older animal groups often were more widespread.
– The closer (geographically) related animals were, the
more likely they were to be similar.
– The further apart two animals, the more time they've
had to evolve in their own direction.
• Using fossil evidence and continental drift,
the distribution of organisms can be
explained (why llamas occur in South
America and their closest living relatives
(camels) live in Asia).

13. Continental Drift
PANGEA
280 million years ago

14. Comparative Anatomy
• Homologous structures—structures that
have a common origin, but may be used for
different things.
• Analogous structures—structures that look
similar, but have different origins (e.g. wings
in birds and insects).

15. Comparative Anatomy
• Homologous Structures: Similar structures in
different living organisms because of a
common ancestor

16. Comparative Anatomy
• Analogous Structures:

17. Comparative Anatomy
• Convergent evolution—animals that are
different evolve similar structures due to
similar environmental pressures. A classic
example is the body shape of fish, dolphins
and ichtyosaurs (extinct). These animals are
unrelated, yet have very similar body shapes.

18. Comparative Anatomy
Convergent Evolution

19. Embryology
• Embryos show common ancestry.
– For example, gill slits in human embryos.
• Many embryos from totally different species look
identical at various stages in their development.

21. Human embryo

22. Embryology

23. Biochemistry
• All organisms use DNA/RNA and proteins as
basis of inheritance
• Similar species have DNA that is very similar.
This can be used to establish lineages and
other relationships.
• This works even on a larger scale such as
between species.
• Can use DNA as a molecular clock to
estimate when organisms diverged (became
different)

24. Biochemistry—Molecular Clock

25. Biochemistry Cytochrome c