Transcript Lecture #11 Date

NOTES: CH 25 - The History of
Life on Earth
History
of Life
Eras
Boundaries
between units in
the Geologic
Time Scale are
marked by
dramatic biotic
change
4500
Origin of Earth
Overview: Lost Worlds
● Past organisms were very different from those
now alive
● The fossil record shows macroevolutionary
changes over large time scales, for example:
– The emergence of terrestrial vertebrates
– The impact of mass extinctions
– The origin of flight in birds
Prebiotic Chemical Evolution:
● Earth’s ancient environment was different
from today:
-very little atmospheric oxygen
-lightning, volcanic activity, meteorite,
bombardment, UV radiation were all more
intense
● Chemical evolution may have
occurred in four stages:
1) abiotic synthesis of monomers
2) joining of monomers into polymers
(e.g. proteins, nucleic acids)
3) formation of protocells (droplets
formed from clusters of molecules)
4) origin of self-replicating molecules
that eventually made inheritance
possible (likely that RNA was first)
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:
Simulated conditions 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.
Number of amino acids
10
0
1953
2008
Mass of amino acids (mg)
20
200
100
0
1953
2008
● Protocells: collections of abiotically
produced molecules able to maintain an
internal environment different from their
surroundings and exhibiting some life
properties such as metabolism,
semipermeable membranes, and
excitability
(experimental evidence
suggests spontaneous
formation of
protocells)
Abiotic genetic replication
possible
formation
of protocells;
self-repliating
RNA
as early
“genes”
Origin of Life - Different Theories:
*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 (self-replicating
molecules) may have preceded nucleic acid
genes.
Phylogeny: the evolutionary history of a
species
● Systematics:
the study of biological
diversity in an
evolutionary context
● The fossil record:
the ordered array of
fossils, within layers,
or strata, of
sedimentary rock
● Paleontologists:
collect and interpret
fossils
● A FOSSIL is the remains or evidence of a
living thing
-bone of an organism or the print of a shell in a
rock
-burrow or tunnel left by an ancient worm
-most common fossils: bones, shells, pollen
grains, seeds.
Figure 25.4
Present
Dimetrodon
Rhomaleosaurus
victor
100 mya
1m
0.5 m
4.5 cm
Coccosteus
cuspidatus
175
200
Tiktaalik
270
300
Hallucigenia
375
400
1 cm
Stromatolites
2.5 cm
500
525
Dickinsonia
costata
565
600
Fossilized
stromatolite
1,500
3,500
Tappania
Examples of different kinds of fossils
PETRIFICATION is the process by which
plant or animal remains are turned into stone
over time. The remains are buried, partially
dissolved, and filled in with stone or other
mineral deposits.
A MOLD is an empty space that has the shape
of the organism that was once there. A CAST
can be thought of as a filled in mold. Mineral
deposits can often form casts.
Thin objects, such as leaves and feathers,
leave IMPRINTS, or impressions, in soft
sediments such as mud. When the sediments
harden into rock, the imprints are preserved
as fossils.
PRESERVATION OF ENTIRE ORGANISMS:
It is quite rare for an entire organism to be
preserved because the soft parts decay easily.
However, there are a few special situations that
allow organisms to be preserved whole.
FREEZING: This prevents substances from
decaying. On rare occasions, extinct species have
been found frozen in ice.
AMBER: When the resin (sap) from certain
evergreen trees hardens, it forms a hard
substance called amber. Flies and other insects
are sometimes trapped in the sticky resin that
flows from trees. When the resin hardens, the
insects are preserved perfectly.
TAR PITS: These are large pools of tar.
Animals could get trapped in the sticky tar
when they went to drink the water that
often covered the pits. Other animals
came to feed on these animals and then
also became trapped.
TRACE FOSSILS: These fossils reveal
much about an animal’s appearance without
showing any part of the animal. They are
marks or evidence of animal activities, such
as tracks, burrows, wormholes, etc.
The fossil record
● Sedimentary rock: rock
formed from sand and mud
that once settled on the
bottom of seas, lakes, and
marshes
Methods for Dating Fossils:
● RELATIVE DATING: used to
establish the geologic time
scale; sequence of species
● ABSOLUTE DATING:
radiometric dating; determine
exact age using half-lives of
radioactive isotopes
Where would you expect to
find older fossils and where
are the younger fossils?
Why?
Relative Dating:
● What is an INDEX FOSSIL?
 fossil used to help determine the relative
age of the fossils around it
 must be easily recognized and must have
existed for a short period BUT over wide
geographical area.
Radiometric Dating:
● Calculating the ABSOLUTE age of fossils
based on the amount of remaining
radioactive isotopes it contains.
Isotope = atom of an element that has a
number of neutrons different from that of
other atoms of the same element
Radiometric Dating:
● Certain naturally occurring elements /
isotopes are radioactive, and they
decay (break down) at predictable rates
● An isotope (the “parent”) loses particles
from its nucleus to form a isotope of the
new element (the “daughter”)
● The rate of decay is expressed in a
“half-life”
Daughter
250
Time
200
150
100
Parent
50
0
0
5
10
Amount
15
20
Fraction of parent
isotope remaining
Figure 25.5
1
Accumulating
“daughter”
isotope
2
Remaining
“parent”
isotope
1
1
4
1
2
3
Time (half-lives)
8
1
4
16
Half life= the amount of time it
takes for ½ of a radioactive
element to decay.
To determine the age of a fossil:
1) compare the amount of the “parent”
isotope to the amount of the
“daughter” element
2) knowing the half-life, do the math to
calculate the age!
Parent Isotope
Daughter
Half-Life
Uranium-238
Lead-206
4.5 billion years
Uranium-235
Lead-207
704 million years
Thorium-232
Lead-208
14.0 billion years
Rubidium-87
Strontium-87
48.8 billion years
Potassium-40
Argon-40
1.25 billion years
Samarium-147
Neodymium-143
106 billion years
Radioactive Dating:
Example: Carbon 14
● Used to date material that was once alive
● C-14 is in all plants and animals
(C-12 is too, but it does NOT decay!)
● When an organism dies, the amount of C-14
decreases because it is being converted back
to N-14 by radioactive decay
Example: Carbon 14
● By measuring the amount of C-14
compared to N-14, the time of death can
be calculated
● C-14 has a half life of 5,730 years
● Since the half life is considered short, it
can only date organisms that have died
within the past 70,000 years
Radioactive Decay of Potassium-40
220
Am ount of Potassium -40 (g)
200
180
160
140
120
100
80
60
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5 10 10.5 11
Time (billions of years)
What is the half-life of Potassium-40?
How many half-lives will it take for Potassium-40 to decay to 50 g?
How long will it take for Potassium-40 to decay to 50 g?
Radioactive Decay of Potassium-40
220
Am ount of Potassium -40 (g)
200
180
160
140
120
100
80
60
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10 10.5 11
Tim e (billions of years)
What is the half-life of Potassium-40? 1.2 billion years
How many half-lives will it take for Potassium-40 to decay to 50 g?
2 half-lives
How long will it take for Potassium-40 to decay to 50g? 2.6 billion yrs.
How is the decay rate of a
radioactive substance expressed?
Equation:
A = Ao x (1/2)n
A = amount remaining
Ao = initial amount
n = # of half-lives
(**to find n, calculate t/T, where t = time, and T =
half-life, in the same time units as t), so you can
rewrite the above equation as:
A = Ao x (1/2)t/T
½ Life Example #1:
● Nitrogen-13 decays to carbon-13 with t1/2
= 10 minutes. Assume a starting mass of
2.00 g of N-13.
A) How long is three half-lives?
B) How many grams of the isotope will still
be present at the end of three half-lives?
½ Life Example #1:
● Nitrogen-13 decays to carbon-13 with t1/2
= 10 minutes. Assume a starting mass of
2.00 g of N-13.
A) How long is three half-lives?
(3 half-lives) x (10 min. / h.l.) =
30 minutes
½ Life Example #1:
● Nitrogen-13 decays to carbon-13 with t1/2
= 10 minutes. Assume a starting mass of
2.00 g of N-13.
B) How many grams of the isotope will still
be present at the end of three half-lives?
2.00 g x ½ x ½ x ½
=
0.25 g
½ Life Example #1:
● Nitrogen-13 decays to carbon-13 with t1/2
= 10 minutes. Assume a starting mass of
2.00 g of N-13.
B) How many grams of the isotope will still
be present at the end of three half-lives?
A = Ao x (1/2)n
A = (2.00 g) x (1/2)3
A = 0.25 g
½ Life Example #2:
● Mn-56 has a half-life of 2.6 hr. What is the
mass of Mn-56 in a 1.0 mg sample of the
isotope at the end of 10.4 hr?
½ Life Example #2:
● Mn-56 has a half-life of 2.6 hr. What is the
mass of Mn-56 in a 1.0 mg sample of the
isotope at the end of 10.4 hr?
A=?
n = t / T = 10.4 hr / 2.6 hr
A0 = 1.0 mg n = 4 half-lives
A = (1.0 mg) x (1/2)4 = 0.0625 mg
½ Life Example #3:
● Strontium-90 has a half-life of 29 years.
What is the mass of strontium-90 in a 5.0
g sample of the isotope at the end of 87
years?
½ Life Example #3:
● Strontium-90 has a half-life of 29 years.
What is the mass of strontium-90 in a 5.0
g sample of the isotope at the end of 87
years?
A=?
n = t / T = 87 yrs / 29 yrs
A0 = 5.0 g
n = 3 half-lives
A = (5.0 g) x (1/2)3
A = 0.625 g
*The history of living organisms and the
history of Earth are inextricably linked:
● Formation and subsequent breakup of
Pangaea affected biotic diversity
BIOGEOGRAPHY: the study of the past and
present distribution of species
● Formation of Pangaea - 250
m.y.a.
(Permian extinction)
● Break-up of Pangaea – 180
m.y.a.
(led to extreme cases of
geographic isolation!)
 EX: Australian marsupials!
Apparent
continental
drift results
from PLATE
TECTONICS
Plate Tectonics:
● At three points in time,
the land masses of
Earth have formed a
supercontinent: 1.1
billion, 600 million, and
250 million years ago
● According to the theory
of plate tectonics,
Earth’s crust is
composed of plates
floating on Earth’s
mantle
Crust
Mantle
Outer
core
Inner
core
Plate Tectonics:
● Tectonic plates move slowly through the process
of continental drift
● Oceanic and continental plates can collide,
separate, or slide past each other
● Interactions between plates cause the formation of
mountains and islands, and earthquakes
Plate Tectonics:
North
American
Plate
Juan de Fuca
Plate
Eurasian Plate
Caribbean
Plate
Philippine
Plate
Arabian
Plate
Indian
Plate
Cocos Plate
Pacific
Plate
Nazca
Plate
South
American
Plate
Scotia Plate
African
Plate
Antarctic
Plate
Australian
Plate
Consequences of Continental
Drift:
● Formation of the supercontinent Pangaea about
250 million years ago had many effects
– A deepening of ocean basins
– A reduction in shallow water habitat
– A colder and drier climate inland
Cenozoic
Present
Figure 25.14
Eurasia
Africa
65.5
South
America
India
Madagascar
135
Mesozoic
Laurasia
251
Paleozoic
Millions of years ago
Antarctica
● The first photosynthetic organisms
released oxygen into the air and altered
Earth’s atmosphere
● Members of Homo sapiens have changed
the land, water, and air on a scale and at a
rate unprecedented for a single species!
(CE)
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 organisms
were prokaryotes
*this is supported by
fossil evidence
(spherical & filamentous
prokaryotes recovered
from 3.5 billion year
old stromatolites in
Australia and Africa)
The First Single-Celled
Organisms
● The oldest known fossils are stromatolites, rocks
formed by the accumulation of sedimentary layers
on bacterial mats
● Stromatolites date back 3.5 billion years ago
● Prokaryotes were Earth’s sole inhabitants from 3.5
to about 2.1 billion years ago
Major Episodes in the History of Life:
● first prokaryotes: 3.5 to 4.0 billion years ago
● photosynthetic bacteria: 2.5-2.7 billion
years ago
Photosynthesis and the
Oxygen Revolution
● Most atmospheric oxygen (O2) is of biological
origin
● This “oxygen revolution” from 2.7 to 2.3 billion
years ago caused the extinction of many
prokaryotic groups
● Some groups survived and adapted using cellular
respiration to harvest energy
Atmospheric O2
(percent of present-day levels; log scale)
Figure 25.8
1,000
100
10
1
0.1
“Oxygen
revolution”
0.01
0.001
0.0001
4
3
2
Time (billions of years ago)
1
0
● 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
ressemble green
algae and funguslike organisms
The First Eukaryotes
● The oldest fossils of eukaryotic cells date back 2.1
billion years
● Eukaryotic cells have a nuclear envelope,
mitochondria, endoplasmic reticulum, and a
cytoskeleton
● The endosymbiont theory proposes that
mitochondria and plastids (chloroplasts and
related organelles) were formerly small
prokaryotes living within larger host cells
● An endosymbiont is a cell that lives within a host
cell
Endosymbiont Theory:
● The prokaryotic ancestors of mitochondria and
plastids probably gained entry to the host cell as
undigested prey or internal parasites
● In the process of becoming more
interdependent, the host and endosymbionts
would have become a single organism
● Serial endosymbiosis supposes that
mitochondria evolved before plastids through a
sequence of endosymbiotic events
Figure 25.9-1
Plasma membrane
Cytoplasm
DNA
Ancestral
prokaryote
Nucleus
Nuclear envelope
Endoplasmic
reticulum
Figure 25.9-2
Plasma membrane
Cytoplasm
DNA
Ancestral
prokaryote
Nucleus
Endoplasmic
reticulum
Nuclear envelope
Aerobic heterotrophic
prokaryote
Mitochondrion
Ancestral
heterotrophic eukaryote
Figure 25.9-3
Plasma membrane
Cytoplasm
DNA
Ancestral
prokaryote
Nucleus
Endoplasmic
reticulum
Photosynthetic
prokaryote
Mitochondrion
Nuclear envelope
Aerobic heterotrophic
prokaryote
Mitochondrion
Plastid
Ancestral
heterotrophic eukaryote
Ancestral photosynthetic
eukaryote
Endosymbiont Theory:
● Key evidence supporting an endosymbiotic origin
of mitochondria and plastids:
– Inner membranes are similar to plasma
membranes of prokaryotes
– Division is similar in these organelles and some
prokaryotes
– These organelles transcribe and translate their
own DNA
– Their ribosomes are more similar to prokaryotic
than eukaryotic ribosomes
The Origin of Multicellularity
● The evolution of eukaryotic cells allowed for a
greater range of unicellular forms
● A second wave of diversification occurred when
multicellularity evolved and gave rise to algae,
plants, fungi, and animals
● plants evolved from green algae
● fungi and animals arose from different
groups of heterotrophic unicellular
organisms
● first animals (soft-bodied invertebrates): 550700 million years ago
● first terrestrial colonization by plants and fungi:
475-500 million years ago
 plants transformed the landscape and created
new opportunities for all forms of life
The Cambrian Explosion
● The Cambrian explosion refers to the sudden
appearance of fossils resembling modern animal
phyla in the Cambrian period (535 to 525 million
years ago)
● A few animal phyla appear even earlier: sponges,
cnidarians, and molluscs
● The Cambrian explosion provides the first
evidence of predator-prey interactions
Sponges
Cnidarians
Echinoderms
Chordates
Brachiopods
Annelids
Molluscs
Arthropods
PROTEROZOIC
Ediacaran
635
PALEOZOIC
Cambrian
605
575
545
515
Time (millions of years ago)
485 0
The “Big Five” Mass Extinction
Events
● In each of the five mass extinction events, more
than 50% of Earth’s species became extinct
Macroevolution
& Phylogeny
Cretaceous mass
extinction
Asteroid impacts may
have caused mass
extinction events
Permian mass
extinction
Extinction of >90% of species
Mass extinctions:
● Permian (250 m.y.a.): 90% of marine
animals; Pangaea merges
● Cretaceous (65 m.y.a.): death of
dinosaurs, 50% of marine species; low
angle comet
NORTH
AMERICA
Yucatán
Peninsula
Chicxulub
crater
Consequences of Mass
Extinctions
● Mass extinction can alter ecological communities
and the niches available to organisms
● It can take from 5 to 100 million years for diversity
to recover following a mass extinction
● The percentage of marine organisms that were
predators increased after the Permian and
Cretaceous mass extinctions
● Mass extinction can pave the way for adaptive
radiations
Predator genera
(percentage of marine genera)
50
40
30
20
10
0
Era
Period
542
E
O
488
Paleozoic
D
S
444 416
359
Mesozoic
Tr
P
C
299
251
J
200
Permian mass
extinction
Time (millions of years ago)
C
145
Cenozoic
P
N
65.5
Q
Cretaceous mass
extinction
0
Adaptive Radiations
● Adaptive radiation is the evolution of diversely
adapted species from a common ancestor
● Adaptive radiations may follow
– Mass extinctions
– The evolution of novel characteristics
– The colonization of new regions
Worldwide Adaptive Radiations
● Mammals underwent an adaptive radiation after
the extinction of terrestrial dinosaurs
● The disappearance of dinosaurs (except birds)
allowed for the expansion of mammals in diversity
and size
● Other notable radiations include photosynthetic
prokaryotes, large predators in the Cambrian, land
plants, insects, and tetrapods
Ancestral
mammal
Monotremes
(5 species)
ANCESTRAL
CYNODONT
Marsupials
(324 species)
Eutherians
(5,010
species)
250
200
150
100
Time (millions of years ago)
50
0
Regional Adaptive Radiations
● Adaptive radiations can occur when organisms
colonize new environments with little competition
● The Hawaiian Islands are one of the world’s great
showcases of adaptive radiation
Figure 25.20
Close North American relative,
the tarweed Carlquistia muirii
Dubautia laxa
KAUAI
5.1
million
MOLOKAI 1.3
million
years OAHU
years
3.7
million
MAUI
LANAI
years
N
Argyroxiphium
sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Evolution is not goal oriented:
● Evolution is like tinkering — it is a process in
which new forms arise by the slight
modification of existing forms
Evolutionary Novelties
● Most novel biological structures evolve in
many stages from previously existing
structures
● Complex eyes have evolved from simple
photosensitive cells independently many
times
● Natural selection can only improve a
structure in the context of its current utility
(a) Patch of pigmented cells
(b) Eyecup
Pigmented cells
(photoreceptors)
Pigmented
cells
Epithelium
Nerve fibers
Nerve fibers
(c) Pinhole camera-type eye
(d) Eye with primitive lens
Epithelium
Cellular
mass
(lens)
Fluid-filled
cavity
(e) Complex camera lens-type eye
Cornea
Cornea
Lens
Retina
Optic
nerve
Pigmented
layer
(retina)
Optic nerve
Optic nerve