1. Chapter
17
The History
of Life

2. 17-1 The Fossil Record
• Studying life’s history is one of the
most fascinating and challenging
parts of biology

7. 17-1 The Fossil Record
• And researchers go about it in
different ways

8. Fossils and Ancient Life
• From the study of fossils,
Paleontologists infer what past life
forms were like and the environment
that they lived
• They also classify them and arrange
them in the order in which they lived
• Together, all of this information is
called The fossil record

9. What the Fossil Record Shows
• Fossils occur in a particular order
• Life has changed over time
• More than 99 percent of all
species that have ever lived have
become extinct

10. Extinct
• When a species dies out

11. How Fossils Form
• For a fossil to form, either the remains
of the organism or some trace of its
presence must be preserved
• The formation of fossils depends on a
precise combination of conditions
• Most fossils form in sedimentary rock

15. Interpreting Fossil Evidence
• More often than not, a Paleontologist must
analyze and interpret a fossil from a few
fossil bits
• When they study fossils, they look at
anatomical similarities and differences
between the fossil and living organisms
• Also a fossils age is extremely important
• Paleontologists determine the age of a
fossil using 2 techniques

16. 1. Relative Dating
• The relative age of a fossil is
determined by comparing its
placement with that of fossils in
other layers of rock

18. Index Fossils
• Used to compare the relative
ages of fossils

20. To be used as an index
fossil, a species must
1. Be easily recognized
2. Existed for a short period of time
3. Have a wide geographical range

21. 2. Radioactive dating
• Used to determine the absolute
age of rocks using radioactive
elements
• Radioactive elements decay or
break down into non-radioactive
elements at a steady rate

22. Half life
• The length of time required for
half of the radioactive atoms in a
sample to decay
• In radioactive dating, scientists
calculate the age of a sample
based on the amounts of
remaining radioactive isotopes it
contains

24. Geologic Time Scale
• Paleontologists use divisions of
the Geologic time scale to
represent evolutionary time

25. Eras
• Divides the time between the
Precambrian and Present

26. Periods
• Subdivides eras

28. Cambrian Explosion

29. Ordovician

30. Silurian

31. Devonian

32. Carboniferous

33. Permian

34. Triassic

35. Jurassic

36. Cretaceous

37. Tertiary

38. Quaternary

39. What would it take to bring on a
new geological era?
1. Change the atmospheres
composition, thus modifying plants
2. Change the distribution and diversity
of species, thereby changing the
future fossil record
3. Acidify the oceans, which will modify
the mineral deposits on the ocean
floor
• Does this sound familiar?

40. New era being proposed
• “Anthropocene”
• New era characterized by the
domination of the planet by one
species…us.

42. 17 – 4 Patterns of Evolution
• Biologists often use the term
macroevolution to refer to large-
scale evolutionary patterns and
the processes that occur over
long periods of time

43. Six important topics in
macroevolution are
1. Extinction
2. Adaptive radiation
3. Convergent evolution
4. Coevolution
5. Punctuated equilibrium
6. Changes in developmental
genes

44. Extinction
• More than 99% of all species that
have ever lived are now extinct
• Usually extinctions happen the way
Darwin proposed
• Sometimes mass extinctions wipe out
entire ecosystems
• Many times mass extinctions are
followed by a burst of evolution that
produces many new species

45. Adaptive Radiation
• When a single species or a small
group of species has evolved into
diverse forms that live in different
ways

47. Convergent Evolution
• When unrelated organisms come
to resemble one another
Ex.) sharks and dolphins

49. Q: How does this happen?
A: Adaptive radiation can happen in
different places and times but in
ecologically similar environments

50. Analogous Structures
• Structures which look and
function similarly but are made up
of parts that don’t share a
common evolutionary history

52. Coevolution
• The process in which 2 species
evolve in response to changes in
each other
Ex.) plants + pollinators
plants + herbivorous insects
bats + moths

53. Plants and Pollinators

54. Hammer Orchid

55. Bats vs. Moths
An Evolutionary Arms Race

56. Rough Skinned Newt vs.
Garter Snake

57. Punctuated Equilibrium
• There is no question among Biologists that
evolution has happened and is happening today
• There are however questions about how fast
evolution happens
• Darwin thought that evolution was slow and
steady. He called this idea Gradualism
• This idea is supported by fossil evidence
• However, the fossil record also shows changes
that have happened over relatively short periods
of time (hundred of thousands-even million-of
years)

58. Punctuated Equilibrium
• Long stable periods of equilibrium
interrupted by brief periods of
more rapid change
• This may be the result of genetic
isolation

60. Developmental Genes and Body Plans
• Biologists have long suspected that
changes in the genes for growth and
differentiation during embryological
development could produce
transformations in body size and
shape
• Until recently, researchers had only
limited ability to affect gene activity in
embryos

61. Developmental Genes and Body Plans
• We can now perform experiments
with gene expression by turning
genes on or off and examining the
results
• Small changes in the timing of cell
differentiation and gene expression
can make the difference between two
completely different phenotypes