Overview
 Geologic events that alter environments change the
course of biological evolution
 Example: Large lake splitting into several small lakes
 Living things change the planet they inhabit
 Example: Evolution of photosynthetic organisms
putting oxygen into the atmosphere
Photosynthetic
Cyanobacteria
26.1
 Cells produced in 4 stages
 1. Abiotic synthesis of AA & nucleotides (organic
compounds)
 2. Joining of monomers into polymers
 3. Packaging into protobionts – droplets with
membranes that maintained an internal chemistry
different from the environment.
 4. Origin of replication that made inheritance possible
 Evidence for each of these 4 stages discussed
1. Synthesis of organic
compounds
 Earth formed about 4.6 billion years ago
 Conditions on early Earth were very different from
today
 “Primitive soup” experiment of Miller and Urey
 Strongly reducing atmosphere





Hydrogen
Methane
Ammonia
Water vapor
Sparks to mimic lightning
Conception of Earth 3
billion years ago
 Extraterrestrial Sources of Organic
Compounds
 Amino acids that reached early Earth aboard
chondrites could have added to the primitive
soup
 Looking to other planets for signs of life
 Present day Mars = no life
 Billions of years ago it was warm, liquid
water, and carbon dioxide in the atmosphere
2. Abiotic synthesis of
polymers
 Researchers have produced amino acids
polymers by dripping solutions of amino acid
monomers onto hot sand, clay, or rock
 Formed spontaneously
3. Protobionts
 Replication and metabolism are essential for life
 Protobionts: aggregates of abiotically produced
molecules surrounded by a membrane or
membrane-like structure.
 Exhibit some properties of life and could have
formed from abiotically produced organic
compounds
4. Origin of replication
 The first genetic material was probably RNA
 Had the ability to copy itself and began to appear in
protobionts
 RNA could have been the template on which DNA
was assembled
 DNA is much more stable and can be replicated more
accurately so as genomes grew DNA grew
 RNA world gave way to a DNA world and RNA took
over its role that we see it in today
26.2 The fossil record
 Fossils are found in
sedimentary rocks
 Index fossils: the strata
at one location can often
be correlated with strata
at another location by
the presence of similar
fossils known as index
fossils
Radiometric dating
 Radiometric dating:
decay of radioactive
isotopes
 Half-life: the number or
years it takes for 50% of
the original sample to
decay
 Carbon-14 has a half life of 5,730 years so it is
useful for dating fossils up to about 75,000
years old
 Potassium-40 used to date much older fossils
(530 million years old)
 Magnetism of rocks can also provide dating
information
Geologic record
 3 Eons
 Archaean & Proterozoic lasted approx. 4 billion years
 These are known as Precambrian
 Phanerozoic eon –the last half billion years is most of the time
multicellular eukaryotic life has existed
 Divided into 3 eras
 Paleozoic
 Mesozoic
 Cenozoic
 Boundaries between eras correspond to times of mass
extinctions seen clearly in the fossil record
Mass Extinctions
 2 mass extinctions have received the most attention
 Permian & Cretaceous
 Permian – at the boundary between Paleozoic
and Mesozoic eras claimed about 96% of marine
animal speices
 Cretaceous – at the boundary between Mesozoic
and Cenozoic eras doomed more than half of all
marine species and many families of terrestrial
plants and animals including the dinosaurs.
 Permian mass extinction caused by volcanic
eruptions that increased the carbon dioxide
and warmed the global climate
 Cretaceous mass extinction caused by an
asteroid or comet hitting the earth that
spewed up dust and blocked sunlight for
several months.
Impact Crater
26.3
 Oldest known fossils
 Date to 3.5 billion years
ago
 Stromatolites
 Composed of layers of
bacteria and sediment
 Found today in a few
warm, shallow, salty bays
Prokaryotes
 Prokaryotes were Earth’s sole inhabitants
 3.5 to about 2 billion years ago
The oxygen revolution
 Earliest types of photosynthesis did not produce
oxygen
 Oxygenic photosynthesis evolved 3.5 billion years
ago in cyanobacteria
 When oxygen started to accumulate in atmosphere
 It posed a challenge for life
 It provided an opportunity to gain abundant energy
from light
 It provided organisms an opportunity to exploit new
ecosystems
26.4 – Eukaryotes
 Oldest fossil eukaryotes
date back 2.1 billion years
 Arose from Endosymbiosis
and genetic exchanges
between prokaryotes
 Endosymbiotic theory states
that chloroplasts &
mitochondria were formerly
prokaryotic organisms living
within larger cells.
Endosymbiosis
 Mitochondria and plastids were formerly small
prokaryotes living within larger host cells
 Gained entry to the host cell as undigested prey or
internal parasites
 The host and endosymbionts would have become a
single organism
 Evidence to support theory:
 Similarities in inner membrane structures and functions
 Both have their own circular DNA
26.5 - Multicellularity
 Evolved several times
in eukaryotes
 Oldest fossils of
eukaryotes, small
algae that lived 1.2
billion years ago
 1st multicellular
organisms were
colonies
Cambrian Explosion
 Most of the major
phyla of animals
appear here
Colonization of land by
plants, fungi, and animals
 Occurred about 500 million years ago
 Adaptations that helped prevent
dehydration made it possible to move out of
water onto land
 Symbiotic relationships between plants and
fungi began at this time and exist today
Continental Drift
 Continents are not fixed but drift across our planet’s
surface on plates of crust that float on a hot
underlying mantle
 Interactions at plate boundaries
 Convergent boundaries (moving together)
 Divergent boundaries (moving apart)
 Transform boundaries (sliding past one another)
 Volcanoes, Earthquakes, mountain building, and
subduction occur at plate boundaries
 The formation and breakup of the
supercontinent Pangaea explain many
biogeographical puzzles
 Land bridges
 Fossils found on 2 continents that can’t swim
 Rock formations
 Apparent puzzle piece fit of the continents
26.6 Taxonomic systems
 Old system was 2 Kingdoms (Plant & Animal)
 5 kingdom system
 Monera, Protists, Plantae, Fungi, Animalia
 3 Domain system has replaced the 5 kingdom
system
 Archaea, Bacteria, Eukarya