The History of The History of Life on EarthLife on Earth

BIOL BIOL 102: 102: General Biology IIGeneral Biology II

Chapter Chapter 2525

Rob Rob SwatskiSwatski Assoc. Prof. BiologyAssoc. Prof. Biology

HACCHACC--YorkYork 1

MacroMacro--evolutionevolution

Changes over large time scales are observed in the fossil record

Emergence of terrestrial

vertebrates

Origin of flight in birds

Long-term impacts of mass

extinctions 2

The First The First CellsCells

1. Abiotic synthesis of small organic

molecules

2. Bonding small molecules into

macromolecules

3. Packaging macromolecules into protocells

4. Origin of self-replicating molecules

3

Synthesis of Synthesis of Organic Organic

CompoundsCompounds

Earth formed 4.6 BYA, along with

rest of solar system

The early atmosphere

contained water vapor & …

… chemicals released by

volcanic eruptions

N2, NOx, CO2, CH4, NH3, H2, H2S

4

AbioticAbiotic Synthesis Synthesis HypothesesHypotheses

Oparin & Haldane (1920’s)

Early atmosphere was a reducing

environment

Miller & Urey

(1953)

Abiotic synthesis of organic molecules in a

reducing atmosphere is possible

5

6

Ma

ss

of

am

ino

ac

ids

(m

g)

Nu

mb

er

of

am

ino

ac

ids

20

10

0

1953 2008

200

100

0

1953 2008

Amino acid synthesis in a simulated volcanic eruption – 2008 reanalysis of Miller study

7

8

9

10

Alternative Alternative AbioticAbiotic Synthesis HypothesesSynthesis Hypotheses

1st organic molecules may

have been synthesized near

volcanoes & deep-sea hydrothermal

vents

Meteorites seeded the Earth with

amino acids

Small organic molecules polymerize

when concentrated on hot sand, clay, or rock

11

AbioticAbiotic Synthesis of Synthesis of MacromoleculesMacromolecules

• RNA monomers have been produced spontaneously from simple molecules

• Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

12

ProtocellsProtocells

Replication & metabolism are key

properties of life & may have appeared together

Protocells may have been fluid-

filled vesicles enclosed by a

membrane-like structure

Display simple replication & metabolism

Also maintain an internal chemical

environment 13

ProtocellProtocell EvidenceEvidence

Protocells can be easily made in the

lab; adding clay increases their

formation

Form spontaneously from abiotically

produced organic molecules

Small membrane-bound droplets

(liposomes) form when lipids are added

to water

Display simple metabolism

14

Time (minutes)

Precursor molecules plus

montmorillonite clay

Precursor

molecules only

Rela

tiv

e t

urb

idit

y,

an

in

de

x o

f ve

sic

le n

um

ber

0 20 40 60 0

0.2

0.4

Vesicle selfVesicle self--assembly in assembly in montmorillonitemontmorillonite clayclay 15

LiposomeLiposome

16

20 µm

Vesicles dividing to Vesicles dividing to produce smallerproduce smaller vesiclesvesicles

17

Phosphate

Maltose

Phosphatase

Maltose

Amylase

Starch

Glucose-phosphate

Glucose-phosphate

Simple Metabolic PathwaySimple Metabolic Pathway 18

19

Which came first…Which came first…

RNA or DNA?RNA or DNA?

RNA & SelfRNA & Self--ReplicationReplication

The 1st genetic material was

probably RNA, not DNA

Special RNA molecules

(ribozymes) can catalyze many

different reactions

Ribozymes can make complementary copies of short

stretches of RNA

20

21

The “RNA The “RNA World”World”

Early protobionts with self-

replicating, catalytic RNA …

… would have been more effective at

using resources & …

… would have increased in number via natural selection

RNA could have provided a

template for the more stable DNA

22

Absorption Absorption of RNAof RNA

Vesicle boundary

1 m

23

24

25

Craig Venter : Craig Venter : The 1The 1stst Synthetic Bacterial Cell Synthetic Bacterial Cell

26

Evidence Evidence from the from the

Fossil RecordFossil Record Fossils reveal changes in

the history of life on Earth

Sedimentary rocks are deposited into layers

(strata) & are the richest source of fossils

Few individuals have fossilized & even fewer have been discovered

The fossil record is biased in favor of species that: existed for a long time,

were abundant, widespread, & had hard

parts 27

28

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

29

RhomaleosaurusRhomaleosaurus victor, victor, a plesiosaur (200a plesiosaur (200--65.5 65.5 myamya))

30

31

DimetrodonDimetrodon,, a large a large carnivorouscarnivorous synapsidsynapsid

more closely related to more closely related to mammals than reptiles mammals than reptiles

(270 (270 myamya))

32

33

TiktaalikTiktaalik (375 (375 myamya))

34

CoccosteusCoccosteus cuspidatuscuspidatus, , a a placodermplacoderm (400 (400 myamya)) 35

36

37

38

HallucigeniaHallucigenia, , Burgess Shale (525 Burgess Shale (525 myamya)) 39

40

2.5 cm EdiacaranEdiacaran (565 (565 myamya) ) –– softsoft--bodied invertsbodied inverts 41

DickinsoniaDickinsonia costatacostata

42

TappaniaTappania, a , a unicellular unicellular eukaryoteeukaryote (1.5 (1.5 byabya))

43

StromatolitesStromatolites (3.b (3.b byabya)) 44

Fossilized Fossilized sstromatolitetromatolite sectionsection

45

46

Fossilized Fossilized CyanobacteriaCyanobacteria

(Blue(Blue--Green Algae)Green Algae)

How Rocks How Rocks & Fossils & Fossils

Are DatedAre Dated Sedimentary strata reveal the relative

ages of fossils

The absolute ages of fossils are determined by

radiometric (radiocarbon) 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 47

Time (halfTime (half--lives)lives)

Accumulating “daughter” isotope

Remaining “parent” isotope

1 2 3 4

1/2

1/4

1/8

1/16

48

The Origin of The Origin of MammalsMammals

Mammals belong to the tetrapod group

Mammalian evolution can be traced using

anatomical evidence

The common ancestor of mammals & reptiles are the synapsids (300

mya)

The most recent common mammalian

ancestors are the therapsids (280 mya) 49

OTHER

TETRAPODS †Dimetrodon

†Very late (non-

mammalian)

cynodonts

Mammals

Syn

ap

sid

s

Th

era

psid

s

Cyn

od

on

ts

Reptiles

(including

dinosaurs and birds)

Temporal

fenestra

Hinge

Temporal

fenestra

Hinge

Synapsid (300 mya)

Therapsid (280 mya)

Key to skull bones

Articular

Quadrate

Squamosal

Dentary

Hinge

Hinge

Hinges

Temporal

fenestra

(partial view)

Early cynodont (260 mya)

Very late cynodont (195 mya)

Later cynodont (220 mya)

Key to skull bones

Articular

Quadrate

Squamosal

Dentary

Origin of solar

system and

Earth

Prokaryotes

Atmospheric oxygen

Archaean

4

3

Proterozoic

2

Animals

Multicellular

eukaryotes

Single-celled

eukaryotes

Colonization

of land

Humans

Cenozoic

1

The First The First Unicellular Unicellular OrganismsOrganisms

The oldest known fossils are

stromatolites (3.5 bya)

Rock-like structures composed of many layers of bacterial mats & sediment

Prokaryotes were the Earth’s only

inhabitants from 3.5 to 2.1 BYA

Microfossils 56

Fossilized Fossilized StromatoliteStromatolite

57

Living SLiving Stromatolitestromatolites

58

59

60

The First The First PhotosynthesisPhotosynthesis

Most atmospheric oxygen (O2) is of biological origin

Bacteria similar to modern cyanobacteria

were the likely O2 source

O2 produced by photosynthesis reacted

with dissolved iron

Precipitated to form banded iron

formations 2.7 bya 61

62

Banded Iron FormationsBanded Iron Formations 63

The Oxygen The Oxygen RevolutionRevolution

Lasted from 2.7 to 2.3 BYA

Oxidation posed a challenge for life &

caused the extinction of many prokaryotic

groups

But, it provided an opportunity to gain energy from light

Allowed organisms to exploit new ecosystems

64

“Oxygen “Oxygen

revolution”revolution”

Time (billions of years ago)

4 3 2 1 0

1,000

100

10

1

0.1

0.01

0.0001

Atm

os

ph

eri

c O

2

(perc

en

t o

f p

resen

t-d

ay levels

; lo

g s

cale

)

0.001

65

The First The First EukaryotesEukaryotes

The oldest eukaryotic cell fossils are 2.1 BYA

old

Endosymbiosis

Mitochondria & plastids (chloroplasts & related organelles)

were once prokaryotes living inside larger host

cells

Endosymbiont: a cell living within a host

cell 66

EndosymbiontEndosymbiont TheoryTheory

Prokaryotic ancestors of mitochondria & plastids probably entered host

cells as undigested prey or internal parasites

As they became more interdependent, the host & endosymbionts became a

single organism

Serial endosymbiosis: mitochondria evolved

before plastids through a series of endosymbiotic

events

Membrane invagination 67

Nucleus

Cytoplasm

DNA

Plasma membrane

Endoplasmic reticulum

Nuclear envelope

AncestralAncestral prokaryoteprokaryote

Serial Serial EndosymbiosisEndosymbiosis

68

Infolding of plasma membrane

Aerobic heterotrophic prokaryote

Mitochondrion

Ancestral heterotrophic Ancestral heterotrophic eukaryoteeukaryote

69

Ancestral photosynthetic Ancestral photosynthetic eukaryoteeukaryote

Photosynthetic prokaryote

Mitochondrion

Plastid

70

Key Evidence Key Evidence Supporting Supporting

EndosymbiosisEndosymbiosis Mitochondria & plastids

have similar inner membrane structures & functions as prokaryotes

Their division is similar to some prokaryotes

They can transcribe & translate their own DNA

Their ribosomes are more like prokaryotic ribosomes

71

The Origin of The Origin of MulticellularityMulticellularity

Eukaryotic cell evolution allowed for more diverse

unicellular forms

A 2nd wave of diversification occurred when multicellularity

evolved

Gave rise to algae, plants, fungi, & animals

Comparisons of DNA sequences date the

common ancestor of multicellular eukaryotes to

1.5 bya 72

Oldest known Oldest known multicellularmulticellular eukaryote fossils eukaryote fossils –– Algae (1.2 BYA)Algae (1.2 BYA)

73

150 µm TwoTwo--Cell StageCell Stage

Fossilized Fossilized Animal Animal

EmbryoEmbryo (575 MYA)(575 MYA)

74

LaterLater StageStage 75

76

“Snowball “Snowball Earth” Earth”

HypothesisHypothesis

Periods of extreme polar glaciation

Life confined to the equatorial region …

… or deep-sea vents

750 to 580 MYA

77

EdiacaranEdiacaran Biota Biota

Evolution of larger organisms

More diverse forms of life

Wide variety of soft-bodied animals

575 to 535 MYA

78

The The Cambrian Cambrian ExplosionExplosion

The sudden appearance of fossils resembling

modern phyla in a relatively short time

period

Huge increase in biodiversity: soft-bodied, shelled, &

segmented animals

First evidence of predator-prey interactions

Cambrian period: 535 to 525 MYA

79 SanctacarisSanctacaris

80

OpabiniaOpabinia

Sponges

Cnidarians

Echinoderms

Chordates

Brachiopods

Annelids

Molluscs

Arthropods

Ediacaran Cambrian

PROTEROZOIC PALEOZOIC

Time (millions of years ago)

635 605 575 545 515 485 0

81

• DNA analyses suggest that many animal phyla diverged before the Cambrian explosion, perhaps as early as 700 million to 1 BYA

• Fossils in China provide evidence of modern animal phyla tens of millions of years before the Cambrian explosion

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

The The Colonization Colonization

of Landof Land Fungi, plants, & animals began to colonize land

around 500 MYA

Fungi & plants likely colonized land together

by 420 MYA

Arthropods & tetrapods are the most

widespread & diverse land animals

Tetrapods evolved from lobe-finned fishes around 365 MYA

83

84

85

What are the challenges to a What are the challenges to a terrestrial lifestyle?terrestrial lifestyle?

Factors Influencing the Factors Influencing the Rise & Fall of Rise & Fall of BiodiversityBiodiversity

Continental drift

Mass extinctions

Adaptive radiations

86

Continental Continental DriftDrift

Earth’s continents move slowly over the

underlying hot mantle

Oceanic & continental plates

Plates collide, separate, or slide past each other

Interactions result in the creation of mountains, islands, & earthquakes

87

Mantle

Crust

Outer

core

Inner

core

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

88

89

ManamManam Volcano, Volcano, Papua New GuineaPapua New Guinea

PangaeaPangaea

90

Mill

ion

s o

f ye

ars

ago

Mill

ion

s o

f ye

ars

ago

135

Me

sozo

icM

eso

zoic

251

Pal

eo

zoic

Pal

eo

zoic

History ofHistory of Continental DriftContinental Drift

91

South America

Mill

ion

s o

f ye

ars

ago

Mill

ion

s o

f ye

ars

ago

65.5

Eurasia

India

Africa

Antarctica

Madagascar

Ce

no

zoic

Ce

no

zoic

Present

92

Effects of the Pangaea Effects of the Pangaea SuperSuper--ContinentContinent

(250 (250 myamya))

A reduction in shallow

water habitat

A colder & drier inland

climate

Climate change as continents

moved toward &

away from the poles

Changes in ocean

circulation patterns

leading to global

cooling 93

Biological Biological Impact of Impact of Pangaea Pangaea BreakBreak--UpUp

Allopatric speciation

Led to the current distribution of plants,

animals, & fossils

Ex: similarity of fossils in areas of South America & Africa

Re-shaped biodiversity via booms & busts

94 CynognathusCynognathus

95

Mass Mass ExtinctionsExtinctions

The fossil record reveals that most species that have ever lived are now

extinct

At times, the extinction rate

increased dramatically

Resulted in 5 mass extinctions

Over 50% of Earth’s species became extinct in each

event 96

Are There Any Are There Any BenefitsBenefits to Extinction?to Extinction?

97

Tota

l ext

inct

ion

rat

eTo

tal e

xtin

ctio

n r

ate

(f

amili

es

pe

r m

illio

n y

ear

s):

Time (millions of years ago)Time (millions of years ago)

Nu

mb

er

of

fam

ilie

s:

Nu

mb

er

of

fam

ilie

s:

CenozoicCenozoic MesozoicMesozoic PaleozoicPaleozoic E O S D C P Tr J

542

0

488 444 416 359 299 251 200 145

Era Period

5

C P N

65.5

0

0

200

100

300

400

500

600

700

800

15

10

20

98

Mass Extinction & the Diversity of LifeMass Extinction & the Diversity of Life

99

Permian Period (299Permian Period (299--251 MYA)251 MYA)

Permian Permian Mass Mass

ExtinctionExtinction Between Paleozoic & Mesozoic eras (250

MYA)

Occurred in < 5 MY

Led to largest mass extinction: 95% of all

marine species & 70% of terrestrial

species

May have been caused by volcanism,

leading to climate change & reduced

oceanic O2 100

101

El Capitan Permian ReefEl Capitan Permian Reef --Guadalupe MountainsGuadalupe Mountains National Park, TXNational Park, TX

Cretaceous Cretaceous Mass Mass

ExtinctionExtinction Between Mesozoic &

Cenozoic eras (65 MYA)

50% of all marine species became

extinct, along with …

… many terrestrial plants & animals,

including most dinosaurs

The presence of iridium in

sedimentary rocks suggests a meteorite

impact 102

NORTH

AMERICA

Yucatán

Peninsula

Chicxulub

crater

103

104

KK--T Boundary: ColoradoT Boundary: Colorado

The The ChicxulubChicxulub Crater Crater (Yucatan Peninsula, (Yucatan Peninsula,

Mexico)Mexico)

105

106

The Sixth The Sixth Mass Mass

ExtinctionExtinction

The current extinction rate is 100-1000X the

normal background rate

Extinction rates tend to increase when

global temperatures increase

Data suggest that a 6th human-caused

Holocene mass extinction is

currently underway

Mass extinctions

Cooler Warmer

Re

lati

ve

ex

tin

cti

on

ra

te o

f m

ari

ne

an

ima

l g

en

era

3

2

1

0

1

2 3 2 1 0 1 2 3 4

Relative temperature

Fossil Extinctions & TemperatureFossil Extinctions & Temperature

107

Consequences Consequences of Mass of Mass

ExtinctionExtinction

Alters ecological communities & available niches

It can take 5-100 MY for diversity to

recover

Creates potential for adaptive radiations

108

Pre

dat

or

gen

era

Pre

dat

or

gen

era

(p

erc

en

tage

of

mar

ine

ge

ne

ra(p

erc

en

tage

of

mar

ine

ge

ne

ra)

Time (millions of years ago)Time (millions of years ago)

CenozoicCenozoic MesozoicMesozoic PaleozoicPaleozoic E O S D C P Tr J

542

0

488 444 416 359 299 251 200 145

Era Period C P N

65.5 0

10

20

30

40

50

109

Mass Extinctions & EcologyMass Extinctions & Ecology

Adaptive Adaptive Radiation of Radiation of

MammalsMammals

Underwent an adaptive radiation after the extinction

of terrestrial dinosaurs

Allowed increase in diversity & size of

mammals

Why?

110

CynodontCynodont

Millions of years agoMillions of years ago

Monotremes (5 sp)

250 150 100 200 50

ANCESTRAL CYNODONT

0

Marsupials (324 sp)

Eutherians (placental mammals; 5,010 sp)

Ancestral mammal

111

Adaptive Radiation of MammalsAdaptive Radiation of Mammals

Other Examples of Other Examples of Adaptive RadiationsAdaptive Radiations

Photosynthetic prokaryotes

Land plants Large Cambrian

predators Insects & tetrapods

112

Close N. Amer. relative, the tarweed Carlquistia muirii

Argyroxiphium sandwicense

Dubautia linearis Dubautia scabra

Dubautia waialealae

Dubautia laxa

HAWAII 0.4 MY

OAHU 3.7 MY

KAUAI 5.1 MY

1.3 MY

MOLOKAI MAUI

LANAI

113 Regional ARegional Adaptivedaptive Radiation on the Hawaiian IslandsRadiation on the Hawaiian Islands

Evolutionary Evolutionary Effects of Effects of

Developmental Developmental GenesGenes

Developmental genes control the …

… rate, timing, & spatial pattern of

development

Major changes in body form can result

Studying genetic mechanisms of change

can provide insight into large-scale

evolutionary change 114

115

Chimpanzee fetus

Chimpanzee adult

Human fetus Human adult

HeterochronyHeterochrony

An evolutionary change in the rate or

timing of developmental events

Can have a significant impact on body shape

Differential growth rates

The contrasting shapes of human &

chimpanzee skulls are due to small changes

in relative growth rates 116

PaedoPaedo--morphosismorphosis

The rate of reproductive development accelerates

compared with somatic

development

The sexually mature species may retain body features that

were juvenile structures in an

ancestral species

Ex: salamanders

117

Cockroach nymphsCockroach nymphs

118

Changes in Changes in Spatial Spatial PatternPattern Evolutionary change

is also due to alterations in genes

controlling the placement &

organization of body parts

Homeotic genes: determine basic

features including:

Location of wing & leg development on a bird

The arrangement of a flower’s parts

119

HoxHox GenesGenes

A class of homeotic genes providing

positional info during development

If Hox genes are expressed in the wrong location, body parts can

be produced in the wrong location

In crustaceans, a swimming appendage

can be produced instead of a feeding appendage

Evolution of vertebrates from invertebrates was

associated with two alterations in Hox genes

120

HoxHox gene expression & limb developmentgene expression & limb development

Limbless regions

Snake embryo Chicken embryo

121

Changes in Changes in GenesGenes

New morphological forms likely come

from gene duplication events that produce new

developmental genes

The evolution of 6-legged insects from a

many-legged crustacean ancestor

has been demonstrated in lab

experiments

Specific changes in the Ubx gene can “turn

off” leg development

Ex: Drosophila & Artemia 122

Hox gene 6 Hox gene 7 Hox gene 8

About 400 mya

Drosophila Artemia

Ubx

123 Origin of the insect body planOrigin of the insect body plan

Changes in Changes in Gene Gene

RegulationRegulation

Changes in body form may be caused by changes in

how developmental genes are regulated instead of

changes in their sequence

Ex: three-spine sticklebacks in lakes have fewer ventral spines than their marine

relatives

The gene sequence stays the same, but the regulation of gene

expression is different in the two groups of fish

124

Marine stickleback embryo

Close-up of ventral surface (spines)

Lake stickleback embryo

Close-up of mouth

No spines

125

Loss of spines in lake stickleback fish: change in the Loss of spines in lake stickleback fish: change in the regulation of regulation of Pitx1Pitx1 gene expressiongene expression

Evolution is Evolution is Not GoalNot Goal--OrientedOriented

Natural selection can only improve a

structure in the context of its current use

New forms arise through the slight

modification of existing forms

Most novel biological structures evolve in many stages from previously existing

structures

Complex eyes evolved independently from

simple photosensitive cells many times 126

(a) Patch of pigmented cells

Optic nerve Pigmented

layer (retina)

Pigmented cells (photoreceptors)

Fluid-filled cavity

Epithelium

Epithelium

(c) Pinhole camera-type eye

Optic nerve

Cornea

Retina

Lens

(e) Complex camera lens-type eye

(d) Eye with primitive lens Optic nerve

Cornea Cellular mass (lens)

(b) Eyecup

Pigmented cells

Nerve fibers Nerve fibers

127

128

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