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

Glucose-phosphate

Phosphorylase

Amylase

Starch

Maltose

Maltose

Phosphate

Simple metabolismSimple reproduction

20 m

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.

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

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to d

aug

hte

r is

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Time (half-lives)

Radiometric dating

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

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

First single-celled organisms – 3.5 bya

Prokaryotes

Billions ofyears ago

1 4

32

Atmosphericoxygen

Billions ofyears ago

1 4

32

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

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

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.

Single-celledeukaryotes

Billions ofyears ago

1 4

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 m

Origin of multicellularity

Multicellulareukaryotes

Billions ofyears ago

1 4

2 3

Animals

Billions ofyears ago

1 4

2 3

Colonization of land 500 mya extensive land adaptations tetrapods 365 mya our human species 195,000 thousand years ago.

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.

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65.5

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Mill

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Cen

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Pal

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North Americ

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Eurasia

AfricaIndiaSouth

America Madagascar

Australia

Antarctica

Laurasia

Gondwana

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.