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Origin of Life on Earth Chapter 25
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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
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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.
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Chemistry, geology, physics – evidence of origin of life.
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1953 Urey Miller experiment (fig 4.2, 25.2).
Abiotic synthesis of organic molecules possible.
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By dripping solutions of amino acids onto hot sand, clay or rock, researchers have been able to produce amino acid polymers.
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Protobionts – abiotically produced molecules surrounded by a membrane – like structure – (fig 25.3)
Glucose-phosphate
Glucose-phosphate
Phosphorylase
Amylase
Starch
Maltose
Maltose
Phosphate
Simple metabolismSimple reproduction
20 m
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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.
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How do we know about the history of life?
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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.
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1
Accumulating“daughter”
isotope
Remaining“parent”isotope
2
14
1 2 3 4
18 1
16
Rat
io o
f p
aren
t is
oto
pe
to d
aug
hte
r is
oto
pe
Time (half-lives)
Radiometric dating
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Geological record: 3 eons – Archean, Proteozoic, Phanerozoic
Phanerozoic has 3 eras marked by mass extinction events – Paleozoic, Mesozoic and Cenozoic.
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Can also use the analogy of a clock
Land plants
Animals
Paleozoic
Meso-
zoic
Ceno-zoic
Origin of solarsystem andEarth
41
2 3Multicellulareukaryotes
Single-celledeukaryotes
Prokaryotes
Atmosphericoxygen
ProterozoicEon
ArchaeanEon
Humans
Billions of years ago
Key events in evolution of life:
First single-celled organisms
First eukaryotes Origin of
multicellularity: Colonization of land
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First single-celled organisms – 3.5 bya
Prokaryotes
Billions ofyears ago
1 4
32
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Atmosphericoxygen
Billions ofyears ago
1 4
32
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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
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First eukaryotes:
2.1 bya – complex organization, organelles
serial endosymbiosis
.
LE 26-13
Plasmamembrane
Cytoplasm
DNA
Ancestralprokaryote
Endoplasmic reticulum
Nuclear envelope
Infolding ofplasma membrane
Engulfing of aerobicheterotrophicprokaryote
Nucleus
Cell with nucleusand endomembranesystem
Mitochondrion
Engulfing ofphotosyntheticprokaryote insome cells
Plastid
Mitochondrion
Ancestralheterotrophiceukaryote
Ancestralphotosynthetic eukaryote
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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.
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Single-celledeukaryotes
Billions ofyears ago
1 4
2 3
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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 m
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Origin of multicellularity
Multicellulareukaryotes
Billions ofyears ago
1 4
2 3
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Animals
Billions ofyears ago
1 4
2 3
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Colonization of land 500 mya extensive land adaptations tetrapods 365 mya our human species 195,000 thousand years ago.
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Continental drift: Movement of continental plates over time.
By about 10 million yearsago, Earth’s youngestmajor mountain range,the Himalayas, formedas a result of India’scollision with Eurasiaduring the Cenozoic.The continents continueto drift today.
By the end of theMesozoic, Laurasiaand Gondwanaseparated into thepresent-day continents.
By the mid-MesozoicPangaea split intonorthern (Laurasia)and southern(Gondwana)landmasses.
At the end of thePaleozoic, all ofEarth’s landmasseswere joined in thesupercontinentPangaea.
0
65.5
135
251
Mill
ion
s o
f ye
ars
ago
Cen
ozo
icM
eso
zoic
Pal
eozo
ic
North Americ
a
Eurasia
AfricaIndiaSouth
America Madagascar
Australia
Antarctica
Laurasia
Gondwana
Pangaea
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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.
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