Transcript Life Science I 83.101.102 Dr. Ekaterina (Kate) Vorotnikova Office

Life Science I
83.101.201
Dr. Ekaterina (Kate) Vorotnikova
Office: Olsen 413b
E-mail: [email protected]
Lecture 31
Early Earth and the Origin of
Life. (Pages 293- 297; 299
Questions: page 316 # 3-4)
Microevolution
The changes over time in allele frequencies in a population
caused by natural selection, mutations, genetic drift and
gene flow.
Small changes over small period of time
Macroevolution
Large changes over long periods of time, evolution on a
large scale.
Speciation – the emergence of a new species – is the
bridge between microevolution and macroevolution
Wings have evolved from vertebrate forelimbs in three groups of land vertebrates:
pterosaurs, bats, and birds
The separate origins of these three wings can be seen in their differences
Different bones support each wing
The flight surfaces of each wing differ
All three wings evolved from the same ancestral tetrapod limb by natural selection.
Major changes over evolutionary time (like the origin of wings) represent
macroevolution that traces the pattern of evolutionary changes over large time
scales
The wing of a pterosaur is
supported by one elongated
finger, holding a skin
membrane reinforced with
thickened fibers. Evolved about
225 mln years ago
Quetzalcoatlus
A bird wing is supported by an elongated forearm, modified wrist and hand
bones, and fused and reduced finger bones. The wing surface is composed
of feathers, which are outgrowths of skin. Evolved about 150 mln years ago
Bat wings are made
of a membrane
supported by the
arm and four
elongated fingers.
The membrane
extends to the hind
limbs and is
attached at the heel.
Evolved about 60 mln
years ago
EARLY EARTH
AND THE ORIGIN
OF LIFE
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– Earth formed 4.6 billion years ago
– By 3.5 billion years ago, photosynthetic bacteria formed
sandy stromatolite mats
– The first living things were much simpler and arose much
earlier (3.9 billion years ago)
A cross-section of a fossilized stromatolite
Stromatolites in the Shark Bay and some other places along Australia’s western cost
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Conditions on early Earth made the origin of life
possible
– A recipe for life
Raw materials
+
Suitable environment
+
Energy sources
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• The possible composition of Earth’s early
atmosphere
– H2O vapor and compounds released from volcanic
eruptions, including N2 and its oxides, CO2, CH4, NH3,
H2, and H2S
• As the Earth cooled, water vapor
condensed into oceans, and most of the
hydrogen escaped into space
• Many energy sources existed on the early
Earth:
– Intense volcanic activity, lightning, and UV
radiation
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Chemical conditions
Physical conditions
Stage 1
Abiotic synthesis
of monomers
Stage 2
Formation of polymers
Stage 3
Stage 4
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Packaging of polymers
into protobionts
Self-replication
Stage 1. Several hypotheses suggest how
organic monomers could have evolved:
1. Monomers came from outer space
2. Monomers came from reaction in the
atmosphere
3. Monomers came from reactions at
hydrothermal vents on the ocean floor
1. Ice confirmed on an Asteroid (Science News, October 2009)
Planetary scientists from the University of Central Florida in Orlando for the
first time confirmed evidence of water-ice, along with organic compounds,
on the surface of the asteroid 24 Themis. It supports the theory that
Asteroids brought both water and organic compounds to the early Earth,
helping lay the foundation for life on the planet.
2. Scientists confirmed the presence of organic molecules in meteorites
By studying meteorites and their bombardment of Earth, a team of researchers
at Imperial College, England, has calculated that the meteorites could have
carried in as many as 10 billion tons of water vapor and carbon dioxide to
the young Earth every year for millions of years. That amount of water,
about 10 times the daily outflow of the Mississippi River, and carbon
dioxide would have been enough to set off a greenhouse effect that
eventually made the Earth warm and wet enough to harbor plants and
creatures.
3. Formic acid (CH2O2), a molecule implicated in the origins
of life, has been found at record levels on a meteorite that
fell into a Canadian lake in 2000.
Space rock yields carbon bounty
The Tagish Lake meteorite formed
before our Solar System (2000,
Canada)
The particular types, or isotopes, of
hydrogen that are found in the
extraterrestrial formic acid show that it
most likely formed in the cold regions
of space before our Solar System
existed.
The Murchison meteorite
contains many types of amino
acids, formic acid and uracil
(1969, Australia)
Team of scientists found uracil in
the Murchison meteorite, but no
measurable amount of thymine.
However, formic acid is known to
help along the reaction that converts
the uracil into thymine.
– In the 1920s, two scientists—the Russian A. I.
Oparin and the British J. B. S. Haldane—
independently proposed that organic molecules
could have formed on the early Earth
– Modern atmosphere is rich in O2, which
oxidizes and disrupts chemical bonds
– The early Earth likely had a reducing
atmosphere.
– In 1953, graduate student Stanley Miller tested
the Oparin-Haldane hypothesis
– Miller set up an airtight apparatus with gases
circulating past an electrical discharge, to
simulate conditions on the early Earth.
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Miller-Urey Experiment, 1953
electrode
electric
spark
stopcock for
adding gases
CH4
NH3
H2
H2O
stopcock for
withdrawing liquid
condenser
boiler
heat
gases
hot water out
cool water in
liquid droplets
small organic molecules
After a week, Miller’s
setup produced abundant
amino acids and other
organic molecules.
Similar experiments used
other atmospheres and
other energy sources, with
similar results
Miller-Urey experiments
demonstrate that Stage 1,
abiotic synthesis of
organic molecules, was
possible on the early
Earth.
Stage 2. Abiotic synthesis of macromolecules, formation of polymers. Scientists
have produced these molecules without enzymes by dripping solutions of organic
monomers onto hot sand, clay, or rock. The heat vaporized the water and
concentrates the monomers that can spontaneously bond together in chains forming
polymers.
Under ventlike conditions organic molecules originate from inorganic ones within
15 min and amino acids form peptides in the presence of iron-nickel sulfides
• Stage 3: Packaging of polymers into
protobionts
– Polymers could have aggregated into
complex, organized, cell-like structures
Microscopic spheres
with membranes made
of lipids.
Protobionts form
spontaneously,
bounded by lipids.
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Stage 4: Self-replication
RNA may have served both as the first genetic material and as the first
enzymes
The first genes may have been short strands of RNA that replicated without
protein support
RNA catalysts or ribozymes may have assisted in this process.
RNA world
A hypothesis for the origin of the first genes
May 14, 2009.
An English chemist John D. Sutherland from the University of Manchester has
found the hidden gateway to the RNA world, the chemical milieu from which the
first forms of life are thought to have emerged on earth some 3.8 billion years ago.
He has solved a problem that for 20 years has thwarted researchers trying to
understand the origin of life--how the building blocks of RNA, called nucleotides,
could have spontaneously assembled themselves in the conditions of the primitive
earth. The discovery, if correct, should set researchers on the right track to solving
many other mysteries about the origin of life.
MAJOR EVENTS
IN THE HISTORY
OF LIFE
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Three eons
Archaean and
Proterozoic lasted 4 billion
years
Phanerozoic is the last ½
billion years
Divided into Paleozoic era,
Mesozoic era, Cenozoic era.
Prokaryotes lived alone on
Earth for 1.5 billion years.
They created our
atmosphere and transformed
Earth’s biosphere.
Virtually all metabolic
pathways evolved within
prokaryotes.
Atmospheric oxygen
appeared 2.7 billion years
ago due to prokaryotic
photosynthesis.
Cellular respiration arose in
prokaryotes, using oxygen to
harvest energy from organic
molecules.
A clock analogy for some key events in the history of Earth and its life.
– The eukaryotic
cell probably
originated as a
community of
prokaryotes, when
small prokaryotes
capable of aerobic
respiration or
photosynthesis
began living in
larger cells
–
Oldest fossils
of eukaryotes
are 2.1 billion
years old
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– Multicellular forms
arose about 1.5
billion years ago
–
The descendents
of these forms
include a variety of
algae, plants,
fungi, animals
– The oldest known
fossils of multicellular
organisms were
small algae, living
1.2 billion years ago
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– The diversity of
animal forms
increased suddenly
and dramatically
about 535–525
million years ago in
the Cambrian
explosion.
– Fungi and plants
colonized land
together 500 million
years ago.
–
Roots of most
plants have
fungal associates
that exchange
water and
minerals for
nutrients
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– Arthropods and
tetrapods are the
most widespread
and diverse land
animals.
– Human lineage
diverged from
apes 7–6 million
years ago.
– Our species
originated 160,000
years ago. Humans
have been around
about 0.04% of the
history of life.
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The fossil record documents the history of life
– The fossil record documents the main
events in the history of life
– The geologic record is defined by major
transitions in life on Earth
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Geologic Record
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