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Transcript
Origin of Life on Earth
Chapter 25




Earth originated about 4.6 billion years ago.
Cloud dust rocks, water vapor.
Settled by 3.9 billion years ago (bya)
First atmosphere was reducing.
Water vapor, nitrogen and its oxides, carbon
dioxide, methane, ammonia, hydrogen,
hydrogen sulfide
How did life originate?

Abiotic (nonliving) synthesis of small organic
molecules, such as amino acids and nucleotides

Joining of these small molecules into
macromolecules including proteins and nucleic
acids

Packaging of these molecules into “protobionts”,
droplets with membranes that maintained an
internal chemistry different from that of the
surroundings

The origin of self replicating molecules that
eventually made inheritance possible.

Chemistry, geology, physics – evidence of
origin of life.
1953 Urey Miller
experiment (fig 4.2,
25.2).
Abiotic synthesis of
organic molecules
possible.

By dripping solutions of amino acids onto hot
sand, clay or rock, researchers have been
able to produce amino acid polymers.

Protobionts – abiotically produced molecules surrounded
by a membrane – like structure – (fig 25.3)
Glucose-phosphate
20 mm
Glucose-phosphate
Phosphorylase
Starch
Amylase
Phosphate
Maltose
Maltose
Simple reproduction
Simple metabolism

RNA was the first genetic material. Also carry
out number of enzyme-like functions, can
form variety of shapes and can replicate –
Protobiont with RNA (limited genetic
information) increased in number.

RNA formed base for DNA template. DNA
world – diverse life forms.
How do we know about the history of life?



Fossils accumulated in
sedimentary rocks
called strata.
Bear evidence of
macroevolution –
major evolutionary
events over large span
of time, like
photosynthesis, mass
extinctions etc.
Incomplete but
substantial record of
evolutionary changes.
Radiometric dating
Ratio of parent isotope
to daughter isotope

Accumulating
“daughter”
isotope
1
2
Remaining
“parent”
isotope
1
1
4
1
2
Time (half-lives)
3
8
1
4
16


Geological record: 3 eons – Archean,
Proteozoic, Phanerozoic
Phanerozoic has 3 eras marked by mass
extinction events – Paleozoic, Mesozoic and
Cenozoic.

Can also
use the
analogy of a
clock
Cenozoic
Humans
Land plants
Animals
Key events in
evolution of life:
 First single-celled
organisms
 First eukaryotes
Multicellular
 Origin of
eukaryotes
multicellularity:
Single-celled
 Colonization of land eukaryotes
Origin of solar
system and
Earth
1
4
Proterozoic
Eon
Archaean
Eon
Billions of years ago
2
3
Prokaryotes
Atmospheric
oxygen

First single-celled organisms – 3.5 bya
1 Billions of 4
years ago
2
3
Prokaryotes
4
1
Billions of
years ago
2
3
Atmospheric
oxygen


First single-celled
organisms – 3.5 bya.
Stromatolites
(prokaryotes binding
film of sediments) cyanobacteria
oxygenated the
atmosphere.
2.7 bya O2
accumulated in the
water and then in the
atmosphere – evidence
rusting of rocks
Cytoplasm
DNA
Plasma
membrane
Ancestral
prokaryote
Infolding of
plasma membrane

First eukaryotes:

2.1 bya – complex
organization,
organelles

serial
endosymbiosis
Endoplasmic reticulum
Nuclear envelope
Nucleus
Engulfing of aerobic
heterotrophic
prokaryote
Cell with nucleus
and endomembrane
system
Mitochondrion
Mitochondrion
Ancestral
heterotrophic
eukaryote
Engulfing of
photosynthetic
prokaryote in
some cells
Plastid
Ancestral
photosynthetic eukaryote
.
Evidence of endosymbiosis:
 In mitochondria and chloroplasts 




Replication similar to prokaryotes
Single circular DNA molecule
DNA not associated with histone proteins
Ribosomes show similar sensitivity to antibiotics
like bacteria
Ribosomes similar in size to those of bacteria.
1
4
of
years ago
Billions
Singlecelled
eukaryotes
2
3

Origin of
multicellularrity:


1.5 bya small algae and
other primitive
eukaryotes. Several ice
ages for 30my
Cambrian explosion –
535 – 525 mya – major
diversification – bigger
organisms, adaptations
for hunting and defense
10 mm

Origin of multicellularity
1
Multicellular
eukaryotes
Billions of
years ago
2
3
4
Animals
1
4
Billions of
years ago
2
3

Colonization of land




500 mya
extensive land adaptations
tetrapods 365 mya
our human species 195,000 thousand years ago.
Cenozoic
0
Mesozoic
135
251
Paleozoic
Continental
drift:
Movement of
continental
plates over
time.
By the end of the
Mesozoic, Laurasia
and Gondwana
separated into the
present-day continents.
65.5
Millions of years ago

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.
By the mid-Mesozoic
Pangaea split into
northern (Laurasia)
and southern
(Gondwana)
landmasses.
At the end of the
Paleozoic, all of
Earth’s landmasses
were joined in the
supercontinent
Pangaea.





Rearrange geography – dramatic effects on life.
All land – drained shallow coastal areas; vast interiors
Supercontinents break – once connected populations
become geographically isolated
Mass extinctions ; thriving communities disappear; five
events - most famous Cretaceous mass extinction 65.5
million years ago. (6th on the way?)
Adaptive radiation – explosion of diversity, species
occupying all niches – large number of species; e.g.
mammals originated about 180mya but worldwide adaptive
radiation 65.5mya.