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

2. Early Earth
4 main stages in this process
Abiotic synthesis of small organic molecules
Monomers into polymers
Protobionts
Origin of self-replicating molecules

3. Synthesis of Organic Compounds on Early Earth
Earth formed about 4.6 billion years ago
Along with the rest of the solar system
Inorganic molecules synthesized due to free energy and absence of oxygen
Monomers served as building blocks for RNA and DNA

4. Extraterrestrial Sources of Organic Compounds
Some of the organic compounds from which the first life on Earth arose
May have come from space
Carbonaceous chondrites (rocks, 1-2% carbon by mass)
Fragments of a 4.5 billion-year-old collected in southern Australia in 1969 contained 80 a.a. similar to those produced by Miller-Urey experiments

5. The “RNA World” and the Dawn of Natural Selection
The first genetic material
Was probably RNA, not DNA
DNA and RNA are carriers of genetic information through transcription, translation and replication
Major features of the genetic code are shared by all modern living systems.

6. Complementary RNA copy
Ribozymes
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
Figure 26.5
Ribozyme
(RNA molecule)
Template
Nucleotides
Complementary RNA copy 3 5

7. From RNA to DNA
DNA
Double stranded DNA is a much more stable repository for genetic information than the more fragile single stranded RNA
Can be replicated more accurately
After DNA appeared, RNA began to take on their modern roles as intermediates in translation of genetic programs
How did RNA sequences come to carry the code for amino acid sequences?

8. Fossils: physical proof
Fossils provide evidence for evolution
Shows: rate of decay of isotopes, relationships with phylogenetic trees, and chemical properties or geographical data
Dating fossils using Radiometric Dating technique
Radioactive isotopes with longer half-lives are used to date older fossils (ex. Potassium -40 with a half life of about 1.3 billion years)

9. The fossil record chronicles a number of occasions
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
Millions of years ago
600
500
400
300
200
100
100
2,500
Number of
taxonomic
families 80
Permian mass
extinction
2,000
Extinction rate 60
1,500
Extinction rate ( )
Number of families ( ) 40
1,000
Cretaceous
mass extinction 20
500
Carboniferous
Proterozoic eon
Cambrian
Ordovician
Devonian
Permian
Cretaceous
Silurian
Paleogene
Neogene
Triassic
Jurassic
Figure 26.8
Paleozoic
Mesozoic
Ceno-
zoic

10. Magnetic reversals of the north and south magnetic poles
Magnetism of Rocks
The magnetism of rocks
Can also provide dating information
Magnetic reversals of the north and south magnetic poles
Have occurred repeatedly in the past
Leave their record on rocks throughout the world

11. Seafloor Spreading

12. The oldest known fossils are stromatolites
Prokaryotes Evolved
The oldest known fossils are stromatolites
Rocklike structures composed of many layers of bacteria and sediment
Which date back 3.5 billion years ago
First Prokaryotes were Earth’s sole inhabitants
From 3.5 to about 2 billion years ago

13. Oxygenic photosynthesis
Probably evolved about 3.5 billion years ago in cyanobacteria
Figure 26.12

14. When oxygen began to accumulate in the atmosphere about 2
When oxygen began to accumulate in the atmosphere about 2.7 billion years ago
It provided an opportunity to gain abundant energy from light
It provided organisms an opportunity to exploit new ecosystems

15. Among the most fundamental questions in biology
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
The theory of endosymbiosis
Proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells

16. The prokaryotic ancestors of mitochondria and plastids
Probably gained entry to the host cell as undigested prey or internal parasites
Figure 26.13
Cytoplasm
DNA
Plasma
membrane
Ancestral
prokaryote
Infolding of
plasma membrane
Endoplasmic
reticulum
Nuclear envelope
Nucleus
Engulfing
of aerobic
heterotrophic
Cell with nucleus
and endomembrane
system
Mitochondrion
eukaryote
Plastid
Engulfing of
photosynthetic
prokaryote in
some cells
Photosynthetic

17. In the process of becoming more interdependent
The host and endosymbionts would have become a single organism
The evidence supporting an endosymbiotic origin of mitochondria and plastids includes
Similarities in inner membrane structures and functions
Both have their own circular DNA

18. Multicellularity evolved several times in eukaryotes
After the first eukaryotes evolved
A great range of unicellular forms evolved
Multicellular forms evolved also

19. 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
Figure 26.15a, b
150 m
200 m
(a) Two-cell stage
(b) Later stage

20. The Colonial Connection
The first multicellular organisms were colonies
Collections of autonomously replicating cells
10 m
Figure 26.16

21. The “Cambrian Explosion”
Most of the major phyla of animals
Appear suddenly in the fossil record that was laid down during the first 20 million years of the Cambrian period
“explosion” included many large animals with hard shells and exoskeletons

22. Plants, fungi, and animals
Molecular evidence
Suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago
Plants, fungi, and animals
Colonized land about 500 million years ago

23. Often, these plates slide along the boundary of other plates
Continental Drift
Often, these plates slide along the boundary of other plates
Pulling apart or pushing against each other
Figure 26.18
North
American
Plate
Caribbean
Juan de Fuca
Cocos Plate
Pacific
Nazca
South
African
Scotia Plate
Antarctic
Arabian
Eurasian Plate
Philippine
Indian
Australian

24. Many important geological processes
Occur at plate boundaries or at weak points in the plates themselves
Volcanoes and
volcanic islands
Trench
Oceanic ridge
Oceanic crust
Seafloor spreading
Subduction zone
Figure 26.19

25. The formation of the supercontinent Pangaea during the late Paleozoic era
And its breakup during the Mesozoic era explain many biogeographic puzzles
Figure 26.20
India collided with
Eurasia just 10 million
years ago, forming the
Himalayas, the tallest
and youngest of Earth’s
major mountain
ranges. The continents
continue to drift.
By the end of the
Mesozoic, Laurasia
and Gondwana
separated into the
present-day continents.
By the mid-Mesozoic,
Pangaea split into
northern (Laurasia)
and southern
(Gondwana)
landmasses.
Cenozoic
North America
Eurasia
Africa
South
America
India
Madagascar
Antarctica
Australia
Laurasia
Mesozoic
Gondwana
At the end of the
Paleozoic, all of
Earth’s landmasses
were joined in the
supercontinent
Pangaea.
Pangaea
Paleozoic
251
135
65.5
Millions of years ago

26. New information has revised our understanding of the tree of life
Molecular Data
Have provided new insights in recent decades regarding the deepest branches of the tree of life

27. Early classification systems had two kingdoms
Plants and animals
Five kingdom
Figure 26.21
Plantae
Fungi
Animalia
Protista
Monera
Eukaryotes
Prokaryotes

28. Reconstructing the Tree of Life: A Work in Progress
A three domain system
Has replaced the five kingdom system
Includes the domains Archaea, Bacteria, and Eukarya
Each domain
Has been split by taxonomists into many kingdoms