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Transcript of 11 Chapter 18 Origin and History of Life Lecture Outline Biology Sylvia S. Mader Michael...
11
Chapter 18Origin and History of Life
Lecture Outline
BiologySylvia S. Mader
Michael Windelspecht
Copyright © McGraw-Hill Education. Permission required for reproduction or display.
See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into
PowerPoint without notes.
Outline
• 18.1 Origin of Life• 18.2 History of Life• 18.3 Geological Factors That Influence
Evolution
2
18.1 Origin of Life • The last universal common ancestor, (LUCA), is
common to all organisms that live, and have lived, on Earth since life began. Today, we say that “life only comes from life.” The molecules of living organisms, called biomolecules,
are organic molecules.• However, the first cells had to arise from nonliving chemicals,
inorganic substances.
Studies in chemistry, evolutionary biology, paleontology, microbiology, and other branches of science help scientists develop hypotheses about life’s origins.
3
Origin of Life
• The earth came into being about 4.6 BYA. • The earth’s mass provides a gravitational field strong
enough to hold an atmosphere.• Primitive Earth atmosphere:
Most likely consisted of:• Water vapor• Nitrogen• Carbon dioxide• Small amounts of hydrogen, methane, ammonia, hydrogen sulfide,
and carbon monoxide• Little free oxygen
Originally too hot for liquid water to form
• As the earth cooled, water vapor condensed to liquid water.
4
Origin of Life
• Four stages in life’s origins Stage 1: Organic monomers evolved from inorganic compounds. Stage 2: Organic polymers were joined to form organic
polymers. Stage 3: Organic polymers became enclosed in membranes to
form protocells or protobionts. State 4: Protobionts acquired the ability to self-replicate.
5
Stages of the Origin of Life
6
xxx
early Earth
Inorganic chemicals
Stage 1
Stage 2
Stage 3
Stage 4
Stage 4
abioticsynthesis
Ch
emic
al E
volu
tio
nB
iolo
gic
al E
volu
tio
nB
iolo
gic
al E
volu
tio
n
Origin of Life:first self-replicating cell
extinct lineages
Common ancestorof all life on Earth orLUCA (last universalcommon ancestor)
extant organisms
RNADNA
origin ofgenetic code
proto cell
plasmamembrane
polymers
polymerization
Small organic molecules
cell
cell
energycapture
LUCA
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Origin of Life
• Evolution of Monomers: Several hypotheses suggest how monomers evolved.
• Monomers came from outer space.– Comets and meteorites, perhaps carrying organic chemicals, have
pelted Earth throughout history.– Organic molecules could have seeded the chemical origin of life on
Earth.– Bacterium-like cells could have been carried to Earth on a meteorite or
comet.
• Monomers came from reactions in the atmosphere.– Oparin/Haldane Hypothesis (early 1900s)
» Suggested organic molecules could be formed in the presence of outside energy sources using atmospheric gases
• Monomers came from reactions at hydrothermal vents.
7
Origin of Life
• Stanley Miller and Harold Urey (1953) Conducted an experiment to test the Oparin/Haldane
hypothesis.• Showed that gases (methane, ammonia, hydrogen, and
water) can react with one another to produce small organic molecules (amino acids, organic acids)
• Strong energy sources Rainfall would have washed organic compounds from
the atmosphere into the ocean. They would have accumulated in the ocean, making it
an organic soup.
8
Miller-Urey Experiment
9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
electrode
cool water in
hot water outstopcock forwithdrawing liquid
stopcock foradding gases
boiler liquid droplets
condenser
electricspark
CH4
NH3
H2
H2O
heat small organic molecules
gases
Chemical Evolution at Hydrothermal Vents
10
© Ralph White/Eureka Premium/Corbis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
plume of hot waterrich in iron-nickel sulfides
hydrothermalvent
Origin of Life• In cells, monomers join to form polymers in the
presence of enzymes. Iron-Sulfur World Hypothesis
• It suggests organic molecules reacted with amino acids to form peptides in the presence of iron-nickel sulfides.
Protein-First Hypothesis• It assumes that protein enzymes arose first.• DNA genes came afterwards.
RNA-First Hypothesis• It suggests only RNA was needed to progress toward formation of the
first cell or cells.• Some viruses have only RNA genes.• DNA genes would have come afterwards.
11
Origin of Life
• Before the first true cell arose, there would have been a protocell or protobiont, the hypothesized precursor to the first true cells.
• A protocell would have an outer membrane and carry on energy metabolism.
• Proteinoids are small polypeptides with catalytic properties.• When proteinoids are placed in water, they form microspheres,
structures made of proteins with many properties of a cell. If lipids are made available to microspheres, lipids become associated with
microspheres, producing a lipid-protein membrane. Lipids placed into water form cell-sized double-layered bubbles called
liposomes.
They may have provided the first membranous boundary.
12
Comparison of Protocell and Modern Cell Plasma Membranes
13
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Protocell Membrane Cell Membrane
hydrophilic “head”
hydrophobic “tail”
phospholipid
outside celloutside protocell
inside protocell inside cell
phospholipid bilayerfatty acid bilayer
d.c.
a. b.
2 fatty acids
individual fatty acid
Structure and Growth of the First Plasma Membrane
14
.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b.
a.
micelle
vesicle
15
Origin of Life• Evolution of the protocell
Nutrition• The process would have had to carry on nutrition in order
to grow.• If organic molecules formed in the atmosphere and were
carried into the ocean by rain, simple organic molecules could have served as food.
– According to this hypothesis, the protocell was a heterotroph, an organism that consumes preformed organic molecules.
• If the protocell evolved at hydrothermal events, it could have carried out chemosynthesis.
– Chemosynthesis is the synthesis of organic molecules by the oxidation of inorganic compounds.
16
Origin of Life
• Evolution of the protocell• Nutrition (cont’d)
Natural selection would have favored cells that could extract energy from carbohydrates to produce ATP.
• Oxygen was not available.• The protocell may have carried on a form of fermentation.• Scientists speculate that it took millions of years for glycolysis,
a metabolic pathway that transforms high-energy chemical bonds into energy for a cell to do work, to evolve completely.
17
Origin of Life
• A Self-Replication System RNA-first hypothesis
• The first cell would have had an RNA gene that directed protein synthesis.
• Reverse transcription could have led to DNA genes.• RNA was responsible for both DNA and protein formation.• Eventually, protein synthesis would have been carried out according
to the central dogma, with information flowing from DNA to RNA to protein.
Protein-first hypothesis• The protocell would have developed a plasma membrane and
enzymes.• Then, DNA and RNA synthesis would have been possible.• After DNA genes evolved, protein synthesis would have been carried
out according to the central dogma. After DNA formed, the genetic code had to evolve.
18.2 History of Life
• Fossils are the remains and traces of past life.• Paleontology is the study of the fossil record.• Most fossils are traces of organisms embedded in
sediment. Sediment is produced by weathering and erosion of rocks. Sediment becomes a recognizable stratum in a
stratigraphic sequence. Strata of the same age tend to contain the similar fossil
assemblages (index fossils) that can be used for relative dating.
This helps geologists determine relative dates of embedded fossils despite upheavals (relative dating).
18
The History of Life
19
Fossils
20
History of Life• Absolute dating assigns an actual date to a fossil.• One absolute dating method relies on radiometric (radioactive)
dating techniques using, for example 14C, which decays to 14N.• Half-life:
The length of time required for half the atoms to change into another stable element
Unaffected by temperature, light, pressure, etc. All radioactive isotopes have a dependable half-life.
• Occurs at a constant rate• Some only fractions of a second• Some billions of years• Most in-between
• Many isotopes are used in absolute dating, and their combined half-lives make them useful over all periods of interest.
21
22
History of Life• The geologic timescale
Divides the history of the earth into• Eras
• Periods
• Epochs
Derives from accumulation of data from the age of fossils in strata all over the world
Life arose during the Precambrian
Geologic Timescale: Cenozoic and Mesozoic Eras
23
Geologic Timescale: Paleozoic and Precambrian Eras
24
History of Life
• The Precambrian includes about 87% of the geological timescale. Little or no atmospheric oxygen in the early atmosphere
Lack of ozone shield allowed UV radiation to bombard Earth
• The first cells came into existence in aquatic environments. Prokaryotes appeared about 3.5 BYA.
Cyanobacteria fossils have been found in ancient stromatolites.
Photosynthetic cyanobacteria added oxygen to the atmosphere.
Aerobic bacteria proliferated in the oxygen-rich atmosphere.
New metabolic pathways evolved.
25
The Tree of Life
26
ARCHAEA
BACTERIA
first cells
photosynthetic bacteria (produce oxygen)
aerobic bacteria
other photosynthetic bacteria (do not produce oxygen)
thermophiles
halophiles
methanogens
mitochondria
chloroplasts
3.5 BYA 543 MYA1.4 BYA2.2 BYA
Archaebacteria
Animals
Fungi
Protists
Plants
Bacteria
2
7
8
EUKARYA
heterotrophicprotists
photosyntheticprotists
1
3
4
5
6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Prokaryote Fossils of the Precambrian
27
a. Stromatolites b. Primaevifilum
0
20
10 m
18.9a: © Francois Gohier/Science Source; 18.9b: © Dr. J. William Schopf
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
History of Life
• Eukaryotic Cells Arise
About 2.1 BYA
• Most are aerobic
• Contain a nucleus as well as other membranous organelles
Endosymbiotic Theory• Mitochondria were probably once free-living aerobic
prokaryotes.• Chloroplasts were probably once free-living photosynthetic
prokaryotes.• A nucleated cell probably engulfed these prokaryotes that
became various organelles. Cilia and flagella may have originated from slender
undulating prokaryotes that attached to the host cell.
28
29
History of Life• Support for the Endosymbiotic Theory
Mitochondria and chloroplasts are similar in size to bacteria.
Mitochondria and chloroplasts have their own DNA and make some of their own proteins.
Mitochondria and chloroplasts divide by binary fission.
The outer membranes of mitochondria and chloroplasts differ.
• The outer membrane resembles a eukaryotic membrane.
• The inner membrane resembles a prokaryotic membrane.
History of Life
• Multicellularity Arises
About 1.4 BYA Separating germ cells from somatic cells may have
contributed to the diversity of organisms. Early multicellular organisms lacked internal organs
and could have absorbed nutrients from the sea. It’s possible that they practiced sexual
reproduction.• Among today’s protists are colonial forms in which some
cells are specialized to produce gametes needed for sexual reproduction.
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Ediacaran Fossils
31
History of Life
• The Paleozoic Era It begins with the Cambrian period. It lasted over 300 million years. It includes three major mass extinction events. An extinction is the total disappearance of all
members of a species or higher taxonomic group. Mass extinction:
• Disappearance of a large number of taxa• Occurred within a relatively short time interval, a few million
years (compared to geological time scale)
32
History of Life
• The abundance of fossils of animals of the Cambrian period may be due to the evolution of outer skeletons.
• The ancestry of all modern animals can be traced to the Cambrian period based on molecular clock data.
• Molecular Clock: Based on hypothesis that
• Changes in base-pair sequences of certain DNA segments occur at a fixed rate.
• The rate is not affected by natural selection or other external factors. When these base-pair sequences are compared between two
species:• Count the number of base-pair differences.• Count tells how long two species have been evolving separately.
33
Sea Life of the Cambrian Period
34
History of Life
• Invasion of land Began around 500 MYA Plants
• Seedless vascular plants date back to the Silurian period.• They later flourished in Carboniferous period.
Invertebrates• Arthropods were the first animals on land.• Outer skeleton and jointed appendages pre-adapted them to live
on land. Vertebrates
• Fishes first appeared in the Ordovician period.• Amphibians first appeared in the Devonian period and diversified
during the Carboniferous period. A mass extinction occurred at the end of the Permian
period.
35
Swamp Forests of the Carboniferous Period
36
History of Life
• The Mesozoic Era Triassic Period
• Nonflowering seed plants became dominant. Jurassic Period
• Dinosaurs achieved enormous size.• Mammals remained small and insignificant.
Cretaceous Period• Dinosaurs declined at the end of the Cretaceous period due
to a mass extinction.• Mammals:
– Began an adaptive radiation – Moved into habitats left vacated by dinosaurs
37
Dinosaurs of the Late Cretaceous Period
38
History of Life• The Cenozoic Era
It is divided into Tertiary and Quaternary periods.
Mammals continued adaptive radiation.
• Several species took to the air.
Flowering plants were already diverse and plentiful. Primate evolution began.
• Some primates adapted to living in trees for protection from predators and to obtain food in the form of fruit.
• Ancestral apes appeared during the Oligocene epoch.
• Megafauna during Pleistocene epoch– Human hunting may have been responsible for the extinction of mammalian megafauna.
39
Mammals of the Oligocene Epoch
40
Woolly Mammoth of the Pleistocene Epoch
41
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Gianni Dagli Orti/Corbis
18.3 Geological Factors That Influence Evolution
• Continental drift The positions of continents and oceans are
not fixed. Plate tectonics
• Earth’s crust consists of slab-like plates.
• Tectonic plates float on a lower hot mantle layer.
• Movements of plates result in continental drift.
• Modern mammalian diversity results from isolated evolution on separate continents.
42
Continental Drift
43
NorthAmerica Eurasia
SouthAmerica
AfricaIndia
Australia
NorthAmerica
Eurasia
AfricaIndia
Australia
Antarctica
SouthAmerica
Laurasia
Gondwana
Pangaea
(251 million years ago) (135 million years ago)
Antarctica
Present day(65 million years ago)
PALEOZOIC MESOZOIC CENOZOIC
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Geological Factors That Influence Evolution
• Mass extinctions occurred at the end of the following periods:
• Ordovician 444 MYA 75% of species
disappeared
• Devonian 360 MYA 70% of marine invertebrates
disappeared
• Permian 251 MYA
90% of species disappeared
• Triassic 20 MYA
60% of species disappeared
• Cretaceous 66 MYA
75% of species disappeared
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Mass Extinctions
46
ammonoids extinct
poriferans
brachiopods
insects
birds
mammals
65.5 MYA
75% 70% 90% 60% 75%
poriferans
brachiopods
mammals
birds
dinosaurs
insects
ammonoids
dinosaurs extinct
CAMBRIAN ORDOVICIAN SILURIAN DEVONIAN CARBONIFEROUS PERMIAN TRIASSIC JURASSIC CRETACEOUS TERTIARYQUARTE-RNARY
PRESENT
199.6 MYA251 MYA359.2 MYAMajorExtinctions
% SpeciesExtinct
443.7 MYA
STATUS TODAY
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