1. The Tree of Life: An Introduction to Biological Diversity
Chapter 26
The Tree of Life: An Introduction to Biological Diversity

2. Overview: Changing Life on a Changing Earth
Life is a continuum extending from the earliest organisms to the variety of species that exist today
Geological events change the course of evolution
Conversely, life changes the planet that it inhabits

4. Geologic history and biological history have been episodic, marked by revolutions that opened many new ways of life

5. Concept 26.1: Conditions on early Earth made the origin of life possible
Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages:
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into polymers
3. Packaging of molecules into “protobionts”
4. Origin of self-replicating molecules

6. Synthesis of Organic Compounds on Early Earth
Earth formed about 4.6 billion years ago, along with the rest of the solar system
Earth’s early atmosphere contained water vapor and chemicals released by volcanic eruptions
Experiments simulating an early Earth atmosphere produced organic molecules from inorganic precursors, but such an atmosphere on early Earth is unlikely

7. LE 26-2 CH4 Water vapor Electrode NH3 H2 Condenser Cold water
Cooled water
containing
organic
molecules
H2O
Sample for
chemical analysis

8. Video: Hydrothermal Vent
Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents
Video: Hydrothermal Vent
Video: Tubeworms

10. Extraterrestrial Sources of Organic Compounds
Some organic compounds from which the first life on Earth arose may have come from space
Carbon compounds have been found in some meteorites that landed on Earth

11. Looking Outside Earth for Clues About the Origin of Life
The possibility that life is not restricted to Earth is becoming more accessible to scientific testing

12. Abiotic Synthesis of Polymers
Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

13. Protobionts
Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure
Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds
For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water

14. LE 26-4
Glucose-phosphate
20 mm
Glucose-phosphate
Phosphorylase
Starch
Amylase
Phosphate
Maltose
Maltose
Simple reproduction
Simple metabolism

15. The “RNA World” and the Dawn of Natural Selection
The first genetic material was probably RNA, not DNA
RNA molecules called ribozymes have been found to catalyze many different reactions, including:
Self-splicing
Making complementary copies of short stretches of their own sequence or other short pieces of RNA

16. Complementary RNA copy 5¢ 5¢
Ribozyme
(RNA molecule) 3¢
Template 3¢
Nucleotides
Complementary RNA copy 5¢ 5¢

17. Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection

18. Concept 26.2: The fossil record chronicles life on Earth
Fossil study opens a window into the evolution of life over billions of years

19. How Rocks and Fossils Are Dated
Sedimentary strata reveal the relative ages of fossils

20. Index fossils are similar fossils found in the same strata in different locations
They allow strata at one location to be correlated with strata at another location
Video: Grand Canyon

22. The absolute ages of fossils can be determined by radiometric dating
The magnetism of rocks can provide dating information
Magnetic reversals of the magnetic poles leave their record on rocks throughout the world

23. Ratio of parent isotope
LE 26-7
Accumulating
“daughter”
isotope
Ratio of parent isotope
to daughter isotope 1 2
Remaining
“parent”
isotope 1 4 1 8 1 16 1 2 3 4
Time (half-lives)

24. The Geologic Record
By studying rocks and fossils at many different sites, geologists have established a geologic record of Earth’s history

25. The geologic record is divided into three eons: the Archaean, the Proterozoic, and the Phanerozoic
The Phanerozoic eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic
Each era is a distinct age in the history of Earth and its life, with boundaries marked by mass extinctions seen in the fossil record
Lesser extinctions mark boundaries of many periods within each era

27. Animation: The Geologic Record
Mass Extinctions
The fossil record chronicles a number of occasions when global environmental changes were so rapid and disruptive that a majority of species were swept away
Animation: The Geologic Record

28. LE 26-8 Millions of years ago 600 500 400 300 200 100 100 2,500
100
2,500
Number of
taxonomic
families 80
2,000
Permian mass
extinction )
Extinction rate 60
1,500
Number of families (
Extinction rate ( 40
1,000
Cretaceous
mass extinction ) 20
500
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Cretaceous
Paleogene
Proterozoic eon
Neogene
Ceno-
zoic
Paleozoic
Mesozoic

29. The Permian extinction killed about 96% of marine animal species and 8 out of 27 orders of insects
It may have been caused by volcanic eruptions
The Cretaceous extinction doomed many marine and terrestrial organisms, notably the dinosaurs
It may have been caused by a large meteor impact

30. LE 26-9
NORTH
AMERICA
Chicxulub
crater
Yucatán
Peninsula

31. Mass extinctions provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches

32. A clock analogy can be used to place major events in the context of the geological record

33. LE 26-10 Ceno- zoic Meso- zoic Humans Paleozoic Land plants Animals
Origin of solar
system and
Earth 1 4
Proterozoic
Eon
Archaean
Eon
Billions of years ago 2 3
Multicellular
eukaryotes
Prokaryotes
Single-celled
eukaryotes
Atmospheric
oxygen

34. Concept 26.3: As prokaryotes evolved, they exploited and changed young Earth
The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria and sediment
Stromatolites date back 3.5 billion years ago

39. The First Prokaryotes
Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2 billion years ago

40. Electron Transport Systems
Electron transport systems were essential to early life
Some of their aspects may precede life itself

41. Photosynthesis and the Oxygen Revolution
The earliest types of photosynthesis did not produce oxygen
Oxygenic photosynthesis probably evolved about 3.5 billion years ago in cyanobacteria

43. Effects of oxygen accumulation in the atmosphere about 2
Effects of oxygen accumulation in the atmosphere about 2.7 billion years ago:
Posed a challenge for life
Provided opportunity to gain energy from light
Allowed organisms to exploit new ecosystems

44. Concept 26.4: Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes
Among the most fundamental questions in biology is how complex eukaryotic cells evolved from much simpler prokaryotic cells

45. The First Eukaryotes
The oldest fossils of eukaryotic cells date back 2.1 billion years

46. Endosymbiotic Origin of Mitochondria and Plastids
The theory of endosymbiosis proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells

47. The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites
In the process of becoming more interdependent, the host and endosymbionts would have become a single organism

48. LE 26-13 Cytoplasm DNA Plasma membrane Ancestral prokaryote
Infolding of
plasma membrane
Endoplasmic reticulum
Nuclear envelope
Nucleus
Engulfing of aerobic
heterotrophic
prokaryote
Cell with nucleus
and endomembrane
system
Mitochondrion
Mitochondrion
Engulfing of
photosynthetic
prokaryote in
some cells
Ancestral
heterotrophic
eukaryote
Plastid
Ancestral
photosynthetic eukaryote

49. Key evidence supporting an endosymbiotic origin of mitochondria and plastids:
Similarities in inner membrane structures and functions
Both have their own circular DNA

50. Eukaryotic Cells as Genetic Chimeras
Endosymbiotic events and horizontal gene transfers may have contributed to the large genomes and complex cellular structures of eukaryotic cells
Eukaryotic flagella and cilia may have evolved from symbiotic bacteria, based on symbiotic relationships between some bacteria and protozoans

51. LE 26-14
50 mm

52. Concept 26.5: Multicellularity evolved several times in eukaryotes
After the first eukaryotes evolved, a great range of unicellular forms evolved
Multicellular forms evolved also

53. The Earliest Multicellular Eukaryotes
Molecular clocks date the common ancestor of multicellular eukaryotes to 1.5 billion years
The oldest known fossils of eukaryotes are of relatively small algae that lived about 1.2 billion years ago

54. Larger organisms do not appear in the fossil record until several hundred million years later
Chinese paleontologists recently described 570-million-year-old fossils that are probably animal embryos

55. 150 mm 200 mm Two-celled stage of embryonic development (SEM)
Later embryonic stage
(SEM)

56. The Colonial Connection
The first multicellular organisms were colonies, collections of autonomously replicating cells

58. Some cells in the colonies became specialized for different functions
The first cellular specializations had already appeared in the prokaryotic world

59. The “Cambrian Explosion”
Most of the major phyla of animals appear in the fossil record of the first 20 million years of the Cambrian period
Two animal phyla, Cnidaria and Porifera, are somewhat older, dating from the late Proterozoic
Molecular evidence suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago

60. LE 26-17 500 Sponges Cnidarians Echinoderms Chordates Brachiopods
Annelids
Molluscs
Arthropods
Early
Paleozoic
era
(Cambrian
period)
Millions of years ago
542
Late
Proterozoic
eon

61. Colonization of Land by Plants, Fungi, and Animals
Plants, fungi, and animals colonized land about 500 million years ago
Symbiotic relationships between plants and fungi are common today and date from this time

62. Continental Drift
The continents drift across our planet’s surface on great plates of crust that float on the hot underlying mantle
These plates often slide along the boundary of other plates, pulling apart or pushing each other

63. LE 26-18
Eurasian Plate
North
American
Plate
Philippine
Plate
Juan de Fuca
Plate
Caribbean
Plate
Arabian
Plate
Indian
Plate
Cocos Plate
South
American
Plate
Pacific
Plate
Nazca
Plate
African
Plate
Australian
Plate
Scotia Plate
Antarctic
Plate

64. Video: Volcanic Eruption
Many important geological processes occur at plate boundaries or at weak points in the plates
Video: Lava Flow
Video: Volcanic Eruption

65. Volcanoes and volcanic islands Trench Oceanic ridge Subduction zone
LE 26-19
Volcanoes and
volcanic islands
Trench
Oceanic ridge
Subduction zone
Oceanic crust
Seafloor spreading

66. The formation of the supercontinent Pangaea during the late Paleozoic era and its breakup during the Mesozoic era explain many biogeographic puzzles

67. LE 26-20 By about 10 million years ago, Earth’s youngest
major mountain range,
the Himalayas, formed
as a result of India’s
collision with Eurasia
during the Cenozoic.
The continents continue
to drift today.
Cenozoic
North America
Eurasia
By the end of the
Mesozoic, Laurasia
and Gondwana
separated into the
present-day continents.
65.5
Africa
South
America
India
Madagascar
Australia
Antarctica
Laurasia
By the mid-Mesozoic
Pangaea split into
northern (Laurasia)
and southern
(Gondwana)
landmasses.
135
Gondwana
Millions of years ago
Mesozoic
At the end of the
Paleozoic, all of
Earth’s landmasses
were joined in the
supercontinent
Pangaea.
251
Pangaea
Paleozoic

68. Concept 26.6: New information has revised our understanding of the tree of life
Molecular data have provided insights into the deepest branches of the tree of life

69. Previous Taxonomic Systems
Early classification systems had two kingdoms: plants and animals
Robert Whittaker proposed five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia

70. LE 26-21
Plantae
Fungi
Animalia
Eukaryotes
Protista
Prokaryotes
Monera

71. Reconstructing the Tree of Life: A Work in Progress
The five kingdom system has been replaced by three domains: Archaea, Bacteria, and Eukarya
Each domain has been split into kingdoms

72. LE 26-22a Chapter 27 Chapter 28 Red algae Chlorophytes Charophyceans
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Gram-positive bacteria
Korarchaeotes
Cercozoans, radiolarians
Diplomonads, parabasalids
Euglenozoans
Euryarchaeotes, crenarchaeotes, nanoarchaeotes
Alveolates (dinoflagellates, apicomplexans, ciliates)
Stramenopiles (water molds, diatoms, golden algae, brown algae)
Domain Archaea
Domain Eukarya
Domain Bacteria
Universal ancestor

73. LE 26-22b Chapter 29 Chapter 30 Chapter 28 Chapter 31 Chapter 32
Chapters 33, 34
Chytrids
Angiosperms
Zygote fungi
Sac fungi
Club fungi
Sponges
Choanoflagellates
Cnidarians (jellies, coral)
Arbuscular mycorrhizal fungi
Seedless vascular plants (ferns)
Gymnosperms
Bryophytes (mosses, liverworts, hornworts)
Amoebozoans (amoebas, slime molds)
Bilaterally symmetrical animals (annelids,
arthropods, molluscs, echinoderms, vertebrates)
Plants
Animals
Fungi