Transcript Early Earth and the Origin of Life (Ch. 26)

Early Earth & the Origin of Life
(Ch. 26)
*The history of living organisms and
the history of Earth are inextricably
linked:
 Formation and subsequent breakup of
Pangaea affected biotic diversity
 The first photosynthetic organism released
oxygen into the air and altered Earth’s
atmosphere
Endosymbiotic Theory
• certain organelles originated as free-living bacteria
that were taken inside another cell as
endosymbionts through endocytosis
Evidence
– structural
• mitochondria & chloroplasts resemble bacterial structure
• both have double membranes
– genetic
• mitochondria & chloroplasts have their own circular DNA, like
bacteria
• Mitochondria and chloroplasts have bacteria-like RNA and
ribosomes (70S as opposed to 80S in eukaryote cytoplasms)
that enable them to make their own proteins and divide
independently of the host cell
– functional
• mitochondria & chloroplasts move freely within the cell
• mitochondria & chloroplasts reproduce independently
from the cell
Lynn Margulis
• Homo sapiens have changed the land, water, and
air on a scale and at a rate unprecedented for a
single species
Figure 2. Sea level is changing.
Observing stations from around the
world report year-to-year changes
in sea level. The reports are
combined to produce a global
average time series. The year 1976
is arbitrarily chosen as zero for
display purpose.
Figure 1. Global warming revealed.
Air temperature measured at
weather stations on continents and
sea temperature measured along
ship tracks on the oceans are
combined to produce a global mean
temperature each year. This 150year time series constitutes the
direct, instrumental record of global
warming.
History of Life on Earth:

Life on Earth originated between 3.5 and 4.0
billion years ago
 Because of the relatively simple structure of
prokaryotes, it is assumed that the earliest
organism were prokaryotes
*this is supported by
fossil evidence
(spherical & filamentous
prokaryotes recovered
from 3.5 billion year
old stromatolites in
Australia and Africa)
Layers of blue-green algae
Major Episodes in the History of Life:
 first prokaryotes- 3.5 to 4.0 billion
years ago
 photosynthetic bacteria- 2.5 billion
years ago
 first eukaryotes- 2 billion years ago
~The oldest
unequivocal remains of
a diversity of
microorganisms occur
in the 2.0 BYO
Gunflint Chert of the
Canadian Shield
~This fauna includes
not only bacteria and
cyanobacteria but also
ammonia consuming
Kakabekia and some
things that resemble
green algae and
fungus-like organisms
 plants evolved from green algae
 fungi and animals arose from different
groups of heterotrophic unicellular
organisms
 first animals (soft-bodied invertebrates)- 700
million years ago
 first terrestrial colonization by plants and
fungi- 475 million years ago
-plants transformed the landscape
and created new opportunities for all
forms of life
Prebiotic Chemical Evolution:
 Earth’s ancient environment was
different from today:
-very little atmospheric oxygen
-lightning, volcanic activity, meteorite,
bombardment, UV radiation all more intense
Oparin / Haldane hypothesis (1920s):
the reducing atmosphere and greater UV
radiation on primitive Earth favored
reactions that built complex organic
molecules from simple monomers as
building blocks
Miller / Urey experiment (1953):
Simulated atmospheric conditions hypothesized
to be on early Earth by constructing an
apparatus containing H2O, H2, CH4, and NH3.
Results:
• They produced amino acids and other organic
molecules.
• Additional follow-up experiments have produced all
20 amino acids, ATP, some sugars, lipids and purine
and pyrimidine bases of RNA and DNA.
Origin of Life - Different Hypotheses:
*No one knows how life actually began on
Earth; experiments indicate key steps that
could have occurred.
 Panspermia: some organic compounds may
have reached Earth by way of meteorites and
comets
meteorite
 Sea floor / Deep-sea vents: hot water
and minerals emitted from deep sea vents
may have provided energy and chemicals
needed for early protobionts
 Simpler hereditary systems (selfreplicating molecules) may have preceded
nucleic acid genes.
 Chemical evolution may have occurred in
four stages:
1) abiotic synthesis of monomers
2) joining of monomers into polymers
(e.g. proteins, nucleic acid)
3) formation of protobionts (droplets
formed from clusters of molecules)
4) origin of heredity (likely that RNA
was first)
Abiotic Synthesis of Polymers
• Researchers have produced amino acid
polymers by dripping amino acid solutions
onto hot sand, clay, or rock
– Form spontaneously without enzymes or
ribosomes
• Polymers are all different (don’t get the
same one each time)
– May have acted as weak catalysts for reactions
on early Earth???
 Protobionts: collections of abiotically
produced molecules (membrane bound) able to
maintain an internal environment different
from their surroundings and exhibiting some
life properties such as metabolism and
excitability
(experimental evidence
suggests spontaneous
formation of
Protobionts; some have
membrane potential/
excitability)
RNA
• RNA can carry out “enzyme-like” functions
(ribozymes)
– Some can make up short segments of RNA
– Some can remove segments of themselves
– Some can act on different molecules (tRNA)
• Reactions are slow
possible
formation
of protobionts;
self-repliating
RNA as early
“genes”
The Major Lineages of Life: the old 5 Kingdom System
Living organisms
Prokaryotic
Eukaryotic
(Monera)
Simple/unicells
Multicellular
(Protista)
Autotrophic
Heterotrophic
(Plantae)
Absorptive
nutrition
Ingestive
nutrition
(Fungi)
(Animalia)
How was the atmosphere of the early earth
different than it is today?
A.
B.
C.
D.
The early earth’s atmosphere contained mostly carbon
monoxide
The early earth’s atmosphere had more oxygen than it has
today
The early earth’s atmosphere contained more single celled
organisms than it does today
The early earth’s atmosphere did not contain oxygen
In the 4-stage hypothesis for the chemical evolution of life,
which of the following is the correct sequence?
A. Synthesize monomers; join monomers; form protobionts; system of
heredity
B. Form protobionts; synthesize monomers; join monomers; system of
heredity
C. System of heredity; join monomers; synthesize monomers; form
protobionts
D. Synthesize monomers; join monomers; system of heredity; form
protobionts
What is a protobiont?
A.
B.
C.
D.
A self-replicating early life form that uses RNA for heredity
A group of monomers that join/bond when temporarily
bonded to materials such as clay or volcanic rock
Early enzymes that were able to join basic amino acids
together
Collection of abiotically produced molecules that can
maintain an internal environment and exhibit some life
properties
What is the name of the alternate hypothesis for the “seeding”
of organic compounds on earth by meteorites & comets?
A. Deep Sea Vent Hypothesis
B. Panspermia
C. Impact Hypothesis
D. Early Earth “Seeding” Hypothesis
In the old 5 Kingdom system used to classify all life,
what are the names of the Kingdoms?
A. Bacteria; Plantae; Animalia; Fungi; Protista
B. Bacteria; Plantae; Animalia; Fungi; Monera
C. Plantae; Animalia; Bacteria; Monera; Protista
D. Plantae; Animalia; Fungi; Monera; Protista