Major Events in Evolution
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4.6 bya – formation of the Earth (Precambrian)
3.5 bya – prokaryotic cells
2.2 bya – eukaryotic cells
600 mya – soft-bodied invertebrates
500 mya – colonization of land plants (Paleozoic)
420 mya – jawless fish
375 mya – bony fish, amphibians, insects
325 mya – first seed plants, reptiles
220 mya – cone-bearing plants (Mesozoic)
175 mya – dinosaurs abundant
80 mya – angiosperms
60 mya – mammals, birds, pollinating insects (Cenozoic)
30 mya – primate groups
2.5 mya – apelike ancestors
0.5 mya – humans appear
Major Events
in Evolution
Life on Earth Between
4.0 and 3.5 Billion Years Ago
• The planet was bombarded with by
huge rock bodies left over from the
formation of the solar system.
• One of them may have dislodged a chunk of
Earth that became the moon.
• The pounding may have generated enough heat
to vaporize all the available water
and prevent seas from forming.
• As Earth began to cool and liquid
water could exist, prokaryotic life
appeared.
Life on Earth Between
3.5 and 2.0 Billion Years Ago
• The fossil record supports that
prokaryotes were the first
organisms on the planet.
• Two main evolutionary branches to the
prokaryotes existed that still exist today,
bacteria and archaea.
Fossilized Ancient Bacterium Living Leptolyngbya Bacterium
Oxygen Began Accumulating in the
Atmosphere About 2.7 Billion Years Ago
• The only photosynthetic prokaryotes that
generate oxygen are called cyanobacteria.
• The free oxygen probably dissolved in the
surrounding water until the seas and lakes
became saturated with the oxygen.
• Once the dissolved iron precipitated from the
water as iron oxide, O2
began to “gas out” of the
water and accumulate in
the atmosphere.
Eukaryotic Life Began By
2.1 Billion Years Ago
• The oxygenation of the atmosphere
coincides with the evolution of
eukaryotic cells.
• With the evolution of eukaryotic cells came
chloroplasts and mitochondrion.
Multicellular Eukaryotes Evolved
By 1.2 Billion Years Ago
• As eukaryotic single-celled
organisms flourished, they gave
rise to a diversity of protists.
• Multicellular eukaryotes also evolved and
gave rise to modern day algae, plants, fungi,
and animals.
Fossilized Algae
Fossilized
Animal Embryo
Animal Diversity Exploded During
the Early Cambrian Period
• 600 mya – First invertebrate
animals appear; porifera
(sponges)
• 543 mya – First cnidarians; jellyfish and hydra
Plants, Fungi, and Animals
Colonized the Land About 500
Million Years Ago
• Challenges that organisms face
as they move from life in the
water to life on land include preventing the
loss of water and reproducing on land.
• Plants had to develop root systems to anchor
themselves and take up water and nutrients.
• Plants also developed a cuticle to prevent
water loss.
Plants, Fungi, and Animals Colonized the
Land About 500 Million Years Ago
• The most widespread and diverse land animals
are the arthropods (mostly insects and spiders)
• The land vertebrates, or tetrapods, evolved from
marine fishes
– Amphibians evolved from fishes
– Reptiles evolved from amphibians
– Both birds and mammals evolved from reptiles
• Most groups of modern mammals were
established about 50 - 60 mya including primates
• The human lineage diverged from other primates
only 5 mya
The Origin of Life
• Biogenesis – life arises only by the
reproduction of preexisting life; Pasteur’s
experiment proved this.
The Origin of Life – How Can Life
Arise From Nonliving Matter?
•
Hypothesis for the origin of life
1. The abiotic synthesis of small organic
molecules, such as amino acids and nucleotides
2. The joining of these small molecules
(monomers) into polymers, including proteins
and nucleic acids
3. The origin of self-replicating molecules that
eventually made inheritance possible
4. The packaging of all these molecules into
“protobionts,” droplets with membranes that
maintained an internal chemistry different from
the surroundings.
Hypothesis For The Origin Of Life
• Oparin and Haldane independently
hypothesized in the 1920s that the early
atmosphere was probably a reducing
atmosphere (electron adding) because there
was less oxygen
• In order for organic
molecules to be
produced, considerable
energy must be
provided –lightning and
intense UV radiation
could provide this
energy
Hypothesis For The Origin Of Life
• In 1953, Stanley
Miller and Harold
Urey tested the
Oparin-Haldane
hypothesis
• They were able to
produce a variety
of amino acids and
other organic
compounds found
in living organisms
today
Hypothesis For The Origin Of Life
• RNA may have been the first genetic material
– Short polymers of ribonucleotides have
been produced abiotically in lab
experiments
– RNA molecules act as catalyst in modern
cells and may have been the first enzymes
(ribozymes)
• RNA could have provided the template on
which DNA nucleotides were assembled
• Once DNA appeared, RNA molecules would
have begun to take on their modern roles
The Five-Kingdom System
• Whittaker’s
five-kingdom
system (1969)
• Classified
living things
on the basis
of cell type
and nutrition
The Three-Domain System