Transcript Evolutionary History and Trees of Life Ch 25 & 26

Ch 25: History of life
…as we understand it
• 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:
• Abiotic synthesis of small organic molecules
• Joining of these small molecules into macromolecules
• Packaging of molecules into protocells
– Membraneous packets of chemicals
Synthesis of Organic Compounds…
• Earth formed about 4.6 billion years ago, along with the
rest of the solar system
• Bombardment of Earth by rocks and ice likely vaporized
water and prevented seas from forming before 4.2 to 3.9
billion years ago
• Earth’s early atmosphere likely contained water vapor and
chemicals released by volcanic eruptions (nitrogen,
nitrogen oxides, carbon dioxide, methane, ammonia,
hydrogen, hydrogen sulfide)
Are the key building blocks of life
hard to come by?
• Amino acids have been found in meteorites
• RNA monomers have been produced spontaneously from
simple molecules
• In water, lipids and other organic molecules can
spontaneously form vesicles with a lipid bilayer
• Adding clay can increase the rate of vesicle formation
• Vesicles exhibit simple reproduction and metabolism and
maintain an internal chemical environment
– Resultprotocells
The fossil record documents this history of life in geologic time
Present
Dimetrodon
100 mya
0.5 m
4.5 cm
Coccosteus
cuspidatus
175
200
1m
270
300
Rhomaleosaurus
victor
Tiktaalik
Hallucigenia
375
400
1 cm
Stromatolites
Fossilized
stromatolite
Figure 25.4
2.5 cm
500
525
Dickinsonia
costata
565
600
1,500
3,500
Tappania
How Rocks and Fossils Are Dated
• Sedimentary strata reveal the relative
ages of fossils
• The absolute ages of fossils can be
determined by radiometric dating
– A “parent” isotope decays to a “daughter”
isotope at a constant rate
– Each isotope has a known half-life, the time
required for half the parent isotope to
decay
Refer to: Keeping Time handout
Limitations of Carbon dating
• Radiocarbon dating can be used to date fossils up to
75,000 years old
• For older fossils, some isotopes can be used to date
sedimentary rock layers above and below the fossil
Geologic record is divided
into the Archaean, the
Proterozoic, and the
Phanerozoic eons
The Phanerozoic encompasses
multicellular eukaryotic life and is
divided into three eras:
Paleozoic, Mesozoic, and Cenozoic
The Cambrian explosion refers to the
sudden appearance of a multitude of
modern body designs (530 million
years ago)
first evidence of predator-prey
interactions
Appearance of selected
animal groups in the fossil
record
Sponges
Cnidarians
And, the colonization of land…
Echinoderms
Fungi, plants, and animals began to
colonize land about 500 million years
ago
Chordates
Brachiopods
Vascular tissue in plants transports
materials internally and appeared by
about 420 million years ago
Annelids
Plants and fungi today form mutually
beneficial associations and likely
colonized land together
Molluscs
Arthropods
Arthropods and tetrapods are the
most widespread and diverse land
animals
Tetrapods evolved from lobe-finned
fishes around 365 million years ago
PROTEROZOIC
Ediacaran
635
PALEOZOIC
Cambrian
605
575
545
515
485 0
Time (millions of years ago)
Figure 25.10
The fossil record shows that most
species that have ever lived are now
extinct…
Further reading: the last parts of Ch 25 that includes Mass
extinctions
Ch 26: Phylogeny and Systematics
• What is meant by
phylogeny?
• Evolutionary history of a
species…
– Based on common ancestry
– Supported by shared
characteristics and genetics
– Documented by fossils and
genetics
Eon > Era > Periods > Epochs
Systematics?
= study of the organismal
diversity of life
How do we make sense of all this
diversity?
Organize it… using fossil, molecular,
and genetic data to infer
evolutionary relationships
Taxonomy & classification
Phylogenies show evolutionaryrelationships
--Diversity of Life
Taxonomy is the ordered
division and naming of
organisms
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Each group is nested
within the level
above
Broad or less specific
More specific
Closely related species belong to the same genus, similar genera are included in a family, etc…
Species that share the same structures, behaviors, etc, can interbreed and produce fertile
offspring.
Systematists depict evolutionary relationships
in branching phylogenetic trees
• Grouped by shared
characters (Evolutionary
relationships)
–
–
–
–
–
–
Embryology
Reproduction strategies
Symmetry (body plan)
Morphology
Feeding mode
Interspecific interactions
(e.g. symbiosis)
– Etc…
•
•
•
A phylogenetic tree represents a hypothesis about evolutionary relationships
Each branch point represents the divergence of two species
Sister taxa are groups that share an immediate common ancestor
Branch point:
where lineages diverge
Taxon A
Taxon B
Taxon C
Sister
taxa
Taxon D
ANCESTRAL
LINEAGE
Taxon E
Taxon F
Taxon G
This branch point
represents the
common ancestor of
taxa A–G.
This branch point forms a
polytomy: an unresolved
pattern of divergence.
Basal
taxon
• Cladistics groups organisms by common descent
• A clade is a group of species that includes an
ancestral species and all its descendants
– Clades can be nested in larger clades, but not all
groupings of organisms qualify as clades
Figure 26.11
Lancelet
(outgroup)
CHARACTERS
Lamprey
Bass
Frog
Turtle
Leopard
Vertebral
column
(backbone)
Hinged jaws
Lancelet
(outgroup)
TAXA
0
1
1
1
1
1
0
0
1
1
1
1
0
0
0
1
1
1
Amnion
0
0
0
0
1
1
Hair
0
0
0
0
0
1
Four walking
legs
Lamprey
Bass
Vertebral
column
Frog
Hinged jaws
Turtle
Four walking legs
Amnion
Leopard
Hair
(a) Character table
(b) Phylogenetic tree
• Historical 5 Kingdom
system… until about
1970
3 domains, many kingdoms