week 11 lectures biol1020h

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

© 2011 Pearson Education, Inc.

•  The origin of life: hypotheses •  Early earth condi5ons and synthesis of

organic compounds on early earth •  Fossil record •  Single‐cell to mul5‐cellular organisms •  Origin of mammals •  Plate tectonics (evidence of related

organisms on different con5nents) •  Mass ex5nc5ons (past and future)

Week 11: The History of Life on Earth (Chapter 25)

First, some background about early earth:

  The earth formed about 4.6 billion years ago, probably condensing from a vast cloud of dust and rocks surrounding a young sun.

 No life could have existed for first 2‐3 million years as collisions from comets from outer space would have bombarded the earth, crea5ng far too much heat (think like Venus today)

  First atmosphere probably mostly water vapor that, as

the earth cooled, condensed into oceans with most hydrogen escaping into space. Atmosphere also contained chemicals from volcanic erup5ons

 What is recent newsworthy event that has as its aim, understanding the origin of earth’s founda5on?

•  In the 1920s, A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a ‘reducing’ environment (i.e., electron-adding). Energy came from lightning and intense UV radiation

•  In 1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules including amino acids, in a reducing atmosphere was possible


Mas

s of

am

ino

acid

s (m

g)

Num

ber o

f am

ino

acid

s

20

10

0 1953 2008

200

100

0 1953 2008

Amino acid synthesis in a simulated atmosphere of early earth based on 1953 (by Miller) and 2008 (by others) experiments

Amino acids have also been found in meteorites. These could have acted as a source for early life. Fragments of a metor that fell in Australia in 1969 contained 80 amino acids.

Results of ‘volcanic atmosphere test’ in 1953 and 2008 (where more control over expt)

•  However, early atmosphere may not have been reducing •  Instead of forming in the atmosphere, the first organic

compounds may have been synthesized near volcanoes or deep-sea vents (first discovered in 1977 near Galapagos Islands)

•  Miller-Urey–type experiments demonstrate that organic molecules could have formed with various possible atmospheres


Amino acids are not sufficient to produce life, because you also need replica5ng organisms

The dawn of the RNA World: Toward func5onal complexity through liga5on of random RNA oligomers. Briones et al. 2009 RNA. 15: 743–749.

1. RNA monomers have been produced spontaneously from simple molecules 2. Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock. 3. These could have been early catalysts for chemical reactions

Did life start from material from Mars?

Benner (2013) has argued that Molybdenum must have arrived from Mars through Meteorites or volcanoes, as only oxidized mineral form of Molybdenum could have catalyzed reac5ons to start the process of replica5on. Only Boron and Molybdenum can stop organic molecules from turning to tar

"It's lucky that we ended up here nevertheless, as certainly Earth has been the be8er of the two planets for sustaining life. If our hypothe=cal Mar=an ancestors had remained on Mars, there might not have been a story to tell."

Stephen Benner in 29 August 2013 Guardian states…

Protocells •  Replication and metabolism are key properties of

life and may have appeared together (but scientists are divided on this point)

•  Protocells may have been fluid-filled vesicles with a membrane-like structure

•  Evidence: In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer (especially when adding soft mineral clay from volcanic ash!)


(b) Reproduction

20 µm

(c) Absorp5on of RNA

Some of these vesicles can perform metabolic reac5ons using external sources. Orange is RNA coated clay par5cles

Figure 25.3a

Time (minutes)

Precursor molecules plus montmorillonite clay

Precursor molecules only R

elat

ive

turb

idity

, an

inde

x of

ves

icle

num

ber

0 20 40 60 0

0.2

0.4

(a) Self-assembly

Abio5cally produced vesicles: structure needed for replica5on processes

1. Early natural selec5on would have favoured forms of RNA best suited to the environment and best able to self‐replicate (i.e., natural selec5on..if it didn’t

reproduce it would not be there through 5me!) 2. RNA could have provided template for some informa5on that was passed on (e.g., gene5c informa5on) and eventually, DNA nucleo5des, a more stable molecule to encode gene5c informa5on. RNA molecules could then have taken on roles as regulators and intermediates in the transla5on of genes

A two‐step process towards DNA replica5on and then all further life on earth

The Beginnings of the RNA WORLD

p‐RNA (pyranosyl‐RNA) pep5de nucleic acid)

Review: Conditions on early Earth made the origin of life possible

•  Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages:

1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into

macromolecules 3. Packaging of molecules into protocells

(maintaining internal chemistry different than surroundings, e.g. vesicles)

4. Origin of self-replicating molecules © 2011 Pearson Education, Inc.

The Fossil Record •  Sedimentary rocks are deposited into layers

called strata and are the richest source of fossils


•  Few individuals have fossilized, and even fewer have been discovered (often fortuitous, e.g., northern Alberta pipeline discovery, Oct 2013, fisherman finding another species of duck-billed dinosaur in Castle River, AB after flood, Aug 2014)

•  The fossil record is biased in favor of species that –  Existed for a long time – Were abundant and widespread –  Had hard parts


Main take‐home messages from fossiliza5on

Tail of 10 m hadrosaur (Duck‐billed Dinosaur)

Dimetrodon

Stromatolites

Fossilized stromatolite

Coccosteus cuspidatus

4.5 cm

0.5 m

2.5 cm

Present

Rhomaleosaurus victor

Tiktaalik

Hallucigenia

Dickinsonia costata

Tappania

1 cm

1 m

100 mya

175 200

300

375 400

500 525

565 600 1,500

3,500

270

How Rocks and Fossils Are Dated: with difficulty because fossils do not incorporate

elements with long half lives

If volcanic ash above is aged at 525 million years ago, and below is 535 mya then the fossils are assumed to be roughly from 530 mya

How Rocks and Fossils Are Dated •  Sedimentary strata reveal the relative ages of fossils

(older occur deeper in sediments) •  The absolute ages of fossils can be determined by

radiometric dating •  A “parent” isotope decays to a “daughter” isotope at a

constant rate •  Each isotope has a known half-life, the time required

for half the parent isotope to decay •  Igneus rock and older sediments aged with uranium

and potassium isotopes that degrade more slowly (e.g., has a half life of 4.5 billion years)


Accumulating “daughter”

isotope

Frac

tion

of p

aren

t is

otop

e re

mai

ning

Remaining “parent” isotope

Time (half-lives) 1 2 3 4

1 2

1 4 1 8 1 16

Figure 25.5

Carbon‐14 has a half life of 5,730 years‐ use ra5os of carbon‐14 to carbon‐12 (non‐decaying), ages fossils up to 75,000 years old; otherwise use age of sediments surrounding fossil or other isotopes

•  The geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons

•  The Phanerozoic encompasses multicellular eukaryotic life

•  The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic

Key events in life’s history include the (1) origins of single-celled and multi-celled

organisms and (2) the colonization of land


Table 25.1a Ph

anerozoic

Table 25.1b Ph

anerozoic

•  Major boundaries between geological divisions correspond to extinction events in the fossil record (e.g., Mesozoic/Cenozoic boundary) or periods of rapid radiation (e.g., the Cambrian explosion at beginning of Paleozoic)


Early creatures: Tubeworms, which were first discovered when the floor of

the Pacific was explored

Mouthless, gutless, legless animals that rely on microbes for food. Seem to have a symbio=c rela=onship with sulfur‐oxidizing prokaryotes

Origin of solar system and Earth

Prokaryotes

Atmospheric oxygen

Archaean

4

3 of y e

Figure 25.7-1


Prokaryotes

Atmospheric oxygen

Archaean

4

3

Proterozoic

2

Animals

Multicellular eukaryotes

Single-celled eukaryotes

1

of y e

Figure 25.7-2


Prokaryotes

Atmospheric oxygen

Archaean

4

3

Proterozoic

2

Animals


Single-celled eukaryotes

Colonization of land

Humans

Cenozoic

1

of y e

Figure 25.7-3

Prokaryotes

1

2 3

4

y

i

o

ll o B

f

Figure 25.UN02

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


Figure 25.UN03

Atmospheric oxygen

1

2 3

4

y

i

o

B

f

Photosynthesis and the Oxygen Revolution

•  Most atmospheric oxygen (O2) is of biological origin

•  O2 produced by oxygenic photosynthesis, reacted with dissolved iron and precipitated out to form banded iron formations


•  By about 2.7 billion years ago, O2 began accumulating in the atmosphere and rusting iron-rich terrestrial rocks

•  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


•  The early rise in O2 was likely caused by ancient cyanobacteria (oxygen-releasing photosynthetic bacteria)

•  A later increase in the rise of O2 might have been caused by the evolution of eukaryotic cells containing chloroplasts


Figure 25.UN04

Single- celled eukaryotes

1

2 3

4

y

i

o

B

f

The First Eukaryotes •  The oldest fossils of eukaryotic cells date back 2.1

billion years


Theory of ‘serial endosymbiosis’

Figure 25.9-1

Plasma membrane

DNA

Cytoplasm

Ancestral prokaryote

Nuclear envelope

Nucleus Endoplasmic reticulum

Serial endosymbiosis

Infolding of plasma membrane

Figure 25.9-2

Plasma membrane

DNA

Cytoplasm


Nuclear envelope


Aerobic heterotrophic prokaryote

Mitochondrion

Ancestral heterotrophic eukaryote

Infolding of plasma membrane

Cell with nucleus and endomembrane system

Figure 25.9-3

Plasma membrane

DNA

Cytoplasm


Nuclear envelope


Aerobic heterotrophic prokaryote

Mitochondrion

Ancestral heterotrophic eukaryote

Photosynthetic prokaryote

Mitochondrion

Plastid

Ancestral photosynthetic eukaryote

•  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 (e.g., mtDNA)

–  Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes


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


Figure 25.UN05


1

2 3

4

y

i

o

B

f

The Earliest Multicellular Eukaryotes •  Comparisons of DNA sequences date the common

ancestor of multicellular eukaryotes to 1.5 billion years ago

•  The oldest known fossils of multicellular eukaryotes are of small algae that lived about 1.2 billion years ago


•  The “snowball Earth” hypothesis (controversial) suggests that periods of extreme glaciation confined simple multicellular life to the equatorial region or deep-sea vents from 750 to 580 million years ago


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

•  The Chinese fossils suggest that “the Cambrian explosion had a long fuse”


Exam news   Exam will consist of mul5ple choice ques5ons (as per mid‐term, NO ESSAY QUESTION)

  Exam is worth 30% of the final mark

  Mul5ple choice ques5ons: 10% of 30% will be based on first half, and 20% of 30% on the second half

  There will be a review lecture on the last day of class (2 December)

  Readings for this week: Chapter 25 only. For next week parts of chapters (exact page numbers will be provided by Prof. Dorken)

Figure 25.UN06

Animals

1

2 3

4

y

i

o

B

f

Figure 25.10

Sponges

Cnidarians

Echinoderms

Chordates

Brachiopods

Annelids

Molluscs

Arthropods

Ediacaran Cambrian PROTEROZOIC PALEOZOIC

Time (millions of years ago) 635 605 575 545 515 485 0

Recent fossil evidence from China suggests living phyla were present 10’s of millions of years previous to Cambrian explosion. DNA evidence also supports this earlier radia=on

Burgess shale Yoho Na5onal Park, BC. (2300 m seabed)

Figure 25.8

“Oxygen revolution”

Time (billions of years ago) 4 3 2 1 0

1,000

100

10

1

0.1

0.01

0.0001

Atm

osph

eric

O2

(per

cent

of p

rese

nt-d

ay le

vels

; log

sca

le)

0.001

Chengjiang Mao5anshan Shales

Theory has it that oxygen finally reached a concentra5on in atmosphere where animals could have a higher energy level. Also as eukaryotes engulfed mitochondria to obtain a higher energy level, predators arose, are generally larger and so more likely to leave traces in fossil record!

Figure 25.UN07 Colonization of land

1

2 3

4

y

ago i

o

ll B

f

The Colonization of Land •  Fungi, plants, and animals began to colonize land

about 500 million years ago •  Vascular tissue in plants transports materials

internally (i.e., vascular plants!) and appeared by about 420 million years ago

•  Plants and fungi today form mutually beneficial associations and likely colonized land together (e.g., mycorrhizae aid in absorption of water and minerals from the soil and obtain their organic nutriets from plants)..present in the oldest fossilized plants.


Fossilized mychorrhiza‐like associa5ons

•  Arthropods and tetrapods together are the most widespread and diverse land animals

•  Tetrapods evolved from lobe-finned fishes (around 365 million years ago, Sarcopterygii (name of sub‐class of bony fisho)

‘Living fossil’ lobe‐finned fish: coelocanths Current distribu5on: East coast of Africa and Indonesia of about 1000 individuals

Neanderthal DNA Find Your Inner Neanderthal! Learn About Neanderthal Lineage.

The Origin of Mammals

•  Mammals are tetrapods, as are amphibians, reptiles and birds..the first vertebrates to walk on land.

•  The evolution of unique mammalian features can be traced through gradual changes in skull morphology over time


Figure 25.6a

OTHER TETRAPODS

†Dimetrodon

†Very late (non- mammalian) cynodonts

Mammals

Synapsids

Therapsids

Cynodonts

Reptiles (including dinosaurs and birds)

Key iden5fica5on feature of mammals is a single bone in the lower jaw (the dentary)(among other features, see BIOL4180H), that hinges differently: can easily see loss of smaller bones in fossils of pre‐mammals

Figure 25.6b

Temporal fenestra

Hinge

Temporal fenestra

Hinge

Synapsid (300 mya)

Therapsid (280 mya)

Key to skull bones

Articular Quadrate

Squamosal Dentary

Figure 25.6c

Hinge

Hinge

Hinges

Temporal fenestra (partial view)

Early cynodont (260 mya)

Very late cynodont (195 mya) (plus early mammals)

Later cynodont (220 mya)

Key to skull bones Articular Quadrate

Squamosal Dentary

Crusafon5a‐ an early true mammal

Thrinaxadon: a late cynodont

•  The history of life on Earth has seen the rise and fall of many groups of organisms (e.g., loss of anaerobic prokaryotes, dinosaurs, dominant amphibians, ancient conifers, etc.)

•  The rise and fall of groups depends on speciation and extinction rates within the group (e.g., more speciation than extinction leads to dominance of that group).

•  Extinction rates have been influenced by plate tectonics (among other things)

The rise and fall of groups of organisms reflect differences in speciation and

extinction rates


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

•  Earth’s crust is composed of plates floating on Earth’s mantle

Crust

Mantle

Outer core

Inner core

Figure 25.13

Juan de Fuca Plate

North American Plate

Caribbean Plate

Cocos Plate

Pacific Plate

Nazca Plate

South American Plate

Eurasian Plate

Philippine Plate

Indian Plate

African Plate

Antarctic Plate

Australian Plate

Scotia Plate

Arabian Plate

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

Figure 25.14a

135

251

Mes

ozoi

c Pa

leoz

oic

Mill

ions

of y

ears

ago

Laurasia

Gondwana

Figure 25.14b

65.5

Pres

ent

Cen

ozoi

c Eurasia

Africa South America

India

Antarctica

Madagascar

Mill

ions

of y

ears

ago

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


The distribution of fossils and living groups reflects the historic movement of continents

–  For example, the similarity of modern ratites (non-flying tall birds) in parts of South America, Australia, New Zealand and Africa is consistent with the idea that these continents were formerly attached


Marsupials originated in what is now Asia and reached Australia via South America while con5nents were s5ll

joined

Sinodelphys szalayi

Mass Extinctions •  The fossil record shows that most species that

have ever lived are now extinct •  Extinction can be caused by changes to a species’

environment •  At times, the rate of extinction has increased

dramatically and caused a mass extinction •  Mass extinction is the result of disruptive global

environmental changes


25

20

15

10

5

0

542 488 444

Era Period

416

E O S D

359 299

C

251

P Tr

200 65.5

J C Mesozoic

P N Cenozoic

0

0

Q

100

200

300

400

500

600

700

800

900

1,000

1,100 To

tal e

xtin

ctio

n ra

te

(fam

ilies

per

mill

ion

year

s):

Num

ber o

f fam

ilies

:

Paleozoic

145

Figure 25.15

The “Big Five” Mass Extinction Events: loss of 50% of species!

Factors that may have contributed to these extinctions

–  Intense volcanism in what is now Siberia – Global warming resulting from the emission of

large amounts of CO2 from the volcanoes –  Reduced temperature gradient from equator to

poles – Oceanic anoxia from reduced mixing of ocean

waters – Meteorites


NORTH AMERICA

Yucatán Peninsula

Chicxulub crater

The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time as the Cenozoic/Mesozoic extinction (65 mya)

Half of all marine species and many terrestrial plants and animals, including most dinosaurs went extinct. Thin layer of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago. Dust clouds caused by the impact would have blocked sunlight and disturbed global climate.

Ancestral mammal

ANCESTRAL CYNODONT

250 200 150 100 50 0 Time (millions of years ago)

Monotremes (5 species)

Marsupials (324 species)

Eutherians (5,010 species)

Adap5ve radia5on of mammals as a result of empty niches created by loss of terrestrial dinosaurs

Consequences of ex5nc5ons

Is a Sixth Mass Extinction Under Way? •  Scientists estimate that the current rate of

extinction is 100 to 1,000 times the typical background rate

•  Extinction rates tend to increase when global temperatures increase (a weak trend)

•  A sixth, human-caused mass extinction is likely to occur unless dramatic action is taken to reduce humans impact on the earth! (‘the emerging Anthropocene’)


Mass extinctions

Cooler Warmer

Rel

ativ

e ex

tinct

ion

rate

of m

arin

e an

imal

gen

era

3

2

1

0

-1

-2 -3 -2 -1 0 1 2 3 4

Relative temperature

Figure 25.17

Source: NOAA 2013

Modern ex5nc5ons: examples

1970s Acornshell Epioblasma haysiana Cumberland and Tennessee River systems in Alabama, Virginia, Tennessee and Kentucky mollusc

1970 Clear Lake Splirail Pogonichthys ciscoides Clear Lake, California fish 1969 Blackfin Cisco Coregonus nigripinnis Lake Huron and Lake Michigan fish 1969 Tubercled Blossom Epioblasma torulosa torulosa Alabama, Illinois, Indiana, Kentucky,

Ohio, Tennessee and West Virginia mollusc 1968 Striped Bass, St. Lawrence Estuary popula5on Morone saxa=lis sp. 3 Quebec

fish 1967 Angled Riffleshell Epioblasma biemarginata Alabama, Kentucky and Tennessee

mollusc 1967 Narrow Catspaw Epioblasma lenior Tennessee River system in Virginia, Tennessee

and Alabama mollusc 1967 Lined Pocketbook Lampsilis binominata Upper Charahoochee and Flint River

systems in Alabama and Georgia mollusc mid 1960s Turgid Blossom Epioblasma turgidula Alabama, Arkansas and Tennessee

mollusc 1964 Bluntnose Shiner Notropis simus simus Rio Grande River in New Mexico and

Texas fish 1964 Lake Ontario Kiyi Coregonus kiyi orientalis Ontario fish 1964 Bay Springs Salamander Plethodon ainsworthi Jasper County, Mississippi

amphibian

Par5al list of the 31+ North American ex5nc5ons since 1960’s…

More EVO‐DEVO! Evolu5onary transforma5on can result from heterchrony…changes in the rate or 5ming of development events.

Chimpanzee fetus and adult

Human fetus and adult

Figure 25.22

Gills

Axolotl: retains larval features of amphibians (including gills) but can breed. An example of paedomorphosis (from ‘paedos’ meaning child and ‘morphosis’ meaning shape or form. Probably result of change at single locus

Figure 25.27

Holocene

Pleistocene

Pliocene

0

5

10

Anchitherium

Mio

cene

15

20

25

30 Olig

ocen

e

Mill

ions

of y

ears

ago

35

40

50

45

55

Eoce

ne

Equus

Pliohippus

Merychippus

Sino

hipp

us

Meg

ahip

pus

Hyp

ohip

pus

Arc

haeo

hipp

us

Para

hipp

us

Mio

hipp

us

Mesohippus

Prop

alae

othe

rium

Pach

ynol

ophu

s

Pala

eoth

eriu

m

Hap

lohi

ppus

Epih

ippu

s

Oro

hipp

us

Hyracotherium relatives

Hyracotherium

Key Grazers Browsers

Hip

pario

n

Neo

hipp

ario

n

Nan

nipp

us

Cal

lippu

s Hip

pidi

on a

nd

clos

e re

lativ

es

Evolu5onary trends: are they predictable or direc5onal?

week 11 lectures biol1020h

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