Evidence of Evolution
Chapter 12

Geologic
Time Scale

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

Formation of Fossils
• Compression fossil - fossil preserved in
sedimentary rock that has undergone physical
compression.

Formation of Fossils
• Petrification -
organic material
converted into
stone through
replacement of
original material
with minerals

Formation of Fossils
• Impression – 2-
dimensional imprint
of organism without
any organic material
left

Formation of Fossils
• Molds and Casts - original
bone or shell dissolves
away, leaving behind empty
space.
• Depression = mold
• Cast = space filled with other
sediments in the shape of
the original organism

Formation of Fossils
• Intact Preservation -
Oozing tree sap traps
insects and other
organisms
• Amber - When the
sap (or resin)
fossilizes

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

Carbon 14 Dating
• Carbon dating - used to date samples to the relative
dates that the sample was from
• Half-life - amount of time it takes for half the
radioactive nuclei in a sample to decay
• Carbon-14 = 5,700 years

Biogeography
• Biogeography – the study of past and present
distributions of organisms
• Continental Drift – movement of major land
masses due to plate tectonics

Continental Drift
PANGEA
280 million years ago

Comparative Anatomy
• .
• Analogous structures - structures that look
similar, but have different origins (e.g. wings
in birds and insects).

Comparative Anatomy
• Homologous Structures - structures that have
a common origin, but may be used for
different things

Comparative Anatomy
• Analogous Structures - structures that look
similar, but have different origins

Comparative Anatomy
• Convergent Evolution - similar structures due
to similar environmental pressures
– Body shape of fish, dolphins and ichtyosaurs
(extinct).

Embryology
• Embryos show common ancestry
– Gill slits in human, chick, fish, amphibian embryos

Biochemistry
• DNA/RNA - All organisms use DNA/RNA and
proteins as basis of inheritance
– Similar species have similar DNA
– Can use whole genomes or single/groups of
genes
– Mitochondrial DNA – does not degrade as
quickly as nuclear DNA
– Y Chromosome – accumulates changes more
slowly than X
– Can use DNA as a molecular clock to estimate
when organisms diverged (became different)

Biochemistry—Molecular Clock

Biochemistry
• Proteins – cytochrome c used in electron
transport chain of cellular respiration