Download The Origin and Early History of Life AP Biology

AP Biology
The Origin and Early History of Life
1
Origin of Life Hypotheses
•
•
•
Special creation
– Supernatural or divine origin
Extraterrestrial origin
– Panspermia: Life from elsewhere in
universe infected Earth
- Testable
Spontaneous origin
- Life originated from inanimate materials
- Testable
2
Reducing Atmosphere
•
Life most likely emerged under hightemperature conditions.
– Early atmosphere is often referred to as a
reducing atmosphere.
ƒ Exact conditions unknown
™ Ample availability of hydrogen atoms
(gain electrons = reduction)
™ Wouldn’t take as much energy to
form C-rich molecules
™ Very little oxygen
3
Origin of Life - Location
•
•
•
•
•
Ocean’s edge
– Bubble hypotheses
Under frozen seas
– Problematic due to necessary conditions
– It was warm
Deep in Earth’s crust
– Byproduct of volcanic activity
Within clay
– Positively-charged clay
Deep-sea vents
– Conditions suitable for Archaea
4
Miller-Urey Experiment
•
Attempted to reproduce early reducing
atmosphere and produce organic
compounds from inorganic materials
– Hydrogen-rich
– Electrical discharge
ƒ Succeeded in producing amino acids
5
Miller-Urey Experiment
• 15% of C in CH4
converted into simple C
compounds
• C compounds combined
to form formic acid, urea
& amino acids (glycine,
alanine)
6
Chemical Evolution
•
Ongoing debate concerning actual path
– RNA World - Molecules could not have
consistently formed without a mechanism
of heredity.
– Protein World - Replication would be
impossible without enzymes.
– Peptide-Nucleic Acid World - RNA is too
unstable, thus a precursor must have
existed.
7
Cell Origin Theories
•
Bubble theories
– Certain molecules spontaneously form
bubbles.
ƒ would serve to shield hydrophobic
regions from contact with water
™ supports ocean’s edge scenario
8
Cell Origin Theories
•
Oparin’s Bubble Hypothesis
– Primary abiogenesis - protobionts allowed
chemical complexity to develop
ƒ Many different bubble scenarios have
been proposed.
™ no agreement about composition or
how the process occurred
9
Bubble Hypothesis
10
Earliest Cells
•
Microfossils have been found in rocks as old
as 2.5 billion years old.
– resemble prokaryotes
ƒ lack nucleus of more complex
eukaryotes
11
Archaebacteria
•
extreme-condition prokaryotes
– lack peptidoglycan in cell walls
ƒ methanogens
ƒ extreme halophiles
ƒ extreme thermophiles
– thought to have split from Bacteria 2 bya.
12
Bacteria
•
second major group of prokaryotes
– strong cell walls
– simpler gene structure
– contains most modern prokaryotes
ƒ includes photosynthetic bacteria
™ cyanobacteria
13
First Eukaryotic Cells
•
Eukaryotes probably arose about 1.5 bya.
– Internal membrane-bound structures such
as mitochondria and chloroplasts are
thought to have evolved via
endosymbiosis.
ƒ Energy-producing bacteria were
engulfed by larger bacteria.
™ beneficial symbiotic relationship
14
Endosymbiosis
15
First Eukaryotic Cells
•
•
Sexual reproduction
– Eukaryotic cells can reproduce sexually,
thus allowing for genetic recombination.
ƒ Genetic variation is the raw material
necessary for evolution.
Multicellularity
– arisen many times among eukaryotes
ƒ fosters specialization
16
Extraterrestrial Life
•
Universe has 1020 stars similar to our sun.
– Conditions may be such that life has
evolved on other worlds in addition to our
own.
ƒ ancient bacteria on Mars.
™ largest moon of Jupiter, Europa,
covered with ice.
¾ liquid water may be underneath
17
18