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 polymers

3. Packaging of molecules into “protobionts”

4. Origin of self-replicating molecules

Synthesis of Organic Compounds on Early Earth

• Earth formed about 4.6 billion years ago, along with the rest of the solar system

• Earth’s early atmosphere contained water vapor and chemicals released by volcanic eruptions

• Experiments simulating an early Earth atmosphere produced organic molecules from inorganic precursors, but such an atmosphere on early Earth is unlikely

Water vaporCH4

NH3 H 2

Electrode

Condenser

Coldwater

Cooled watercontainingorganicmolecules

Sample forchemical analysis

H2O

• Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents

• Some organic compounds from which the first life on Earth arose may have come from space

• Carbon compounds have been found in some meteorites that landed on Earth

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

Protobionts

• Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure

• Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds

• For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water

Glucose-phosphate

Glucose-phosphate

Phosphorylase

Amylase

Starch

Maltose

Maltose

Phosphate

Simple metabolismSimple reproduction

20 m

The “RNA World” and the Dawn of Natural Selection

• The first genetic material was probably RNA, not DNA

• RNA molecules called ribozymes have been found to catalyze many different reactions, including:

– Self-splicing

– Making complementary copies of short stretches of their own sequence or other short pieces of RNA

Nucleotides

Template

3

3

5 5

Ribozyme(RNA molecule)

Complementary RNA copy

• Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection

• Fossil study opens a window into the evolution of life over billions of years

• Sedimentary strata reveal the relative ages of fossils

• Index fossils are similar fossils found in the same strata in different locations

• They allow strata at one location to be correlated with strata at another location

• The absolute ages of fossils can be determined by radiometric dating

• The magnetism of rocks can provide dating information

• Magnetic reversals of the magnetic poles leave their record on rocks throughout the world

1

Accumulating“daughter”

isotope

Remaining“parent”isotope

2

14

1 2 3 4

18 1

16

Rat

io o

f p

aren

t is

oto

pe

to d

aug

hte

r is

oto

pe

Time (half-lives)

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

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

• Each era is a distinct age in the history of Earth and its life, with boundaries marked by mass extinctions seen in the fossil record

• Lesser extinctions mark boundaries of many periods within each era

The Geologic Record

Mass Extinctions

• The fossil record chronicles a number of occasions when global environmental changes were so rapid and disruptive that a majority of species were swept away

Millions of years ago

600 500 400 300 200 100

Permian massextinction

100

80

60

40

20

0

Extinction rate

Cretaceousmass extinction

02,500

2,000

1,500

1,000

500

0

Neo

gen

e

Pro

tero

zoic

eo

n

Cam

bri

an

Ord

ovi

cian

Silu

rian

Dev

on

ian

Car

bo

nif

ero

us

Per

mia

n

Tri

assi

c

Jura

ssic

Cre

tace

ou

s

Pal

eog

ene

Paleozoic MesozoicCeno-zoic

Nu

mb

er of fam

ilie s ()E

xtin

ctio

n r

ate

()

Number oftaxonomic

families

• The Permian extinction killed about 96% of marine animal species and 8 out of 27 orders of insects

• It may have been caused by volcanic eruptions

• The Cretaceous extinction doomed many marine and terrestrial organisms, notably the dinosaurs

• It may have been caused by a large meteor impact

• Mass extinctions provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches

NORTHAMERICA

ChicxulubcraterYucatán

Peninsula

Land plants

Animals

Paleozoic

Meso-

zoic

Ceno-zoic

Origin of solarsystem andEarth

41

2 3Multicellulareukaryotes

Single-celledeukaryotes

Prokaryotes

Atmosphericoxygen

ProterozoicEon

ArchaeanEon

Humans

Billions of years ago

As prokaryotes evolved, they exploited and changed young Earth

• The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria and sediment

• Stromatolites date back 3.5 billion years ago

• Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2 billion years ago

Electron Transport Systems…Photosynthesis and the Oxygen Revolution

• Electron transport systems were essential to early life

• Oxygenic photosynthesis probably evolved about 3.5 billion years ago in cyanobacteria

• Effects of oxygen accumulation in the atmosphere about 2.7 billion years ago:

– Posed a challenge for life

– Provided opportunity to gain energy from light

– Allowed organisms to exploit new ecosystems

Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes

• Among the most fundamental questions in biology is how complex eukaryotic cells evolved from much simpler prokaryotic cells

• The oldest fossils of eukaryotic cells date back 2.1 billion years

• The theory of endosymbiosis proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells

• 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

Plasmamembrane

Cytoplasm

DNA

Ancestralprokaryote

Endoplasmic reticulum

Nuclear envelope

Infolding ofplasma membrane

Engulfing of aerobicheterotrophicprokaryote

Nucleus

Cell with nucleusand endomembranesystem

Mitochondrion

Engulfing ofphotosyntheticprokaryote insome cells

Plastid

Mitochondrion

Ancestralheterotrophiceukaryote

Ancestralphotosynthetic eukaryote

• Key evidence supporting an endosymbiotic origin of mitochondria and plastids:

– Similarities in inner membrane structures and functions

– Both have their own circular DNA

Eukaryotic Cells as Genetic Chimeras

• Endosymbiotic events and horizontal gene transfers may have contributed to the large genomes and complex cellular structures of eukaryotic cells

• Eukaryotic flagella and cilia may have evolved from symbiotic bacteria, based on symbiotic relationships between some bacteria and protozoans

50 m

150 m 200 m

Two-celled stage of embryonicdevelopment (SEM)

Later embryonic stage(SEM)

Continental Drift

• The continents drift across our planet’s surface on great plates of crust that float on the hot underlying mantle

• These plates often slide along the boundary of other plates, pulling apart or pushing each other

• Many important geological processes occur at plate boundaries or at weak points in the plates

NorthAmericanPlate

Eurasian Plate

PhilippinePlate

IndianPlate

ArabianPlate

AustralianPlate

AntarcticPlate

AfricanPlate

Scotia Plate

SouthAmericanPlateNazca

Plate

PacificPlate

Cocos Plate

Juan de FucaPlate

CaribbeanPlate

Volcanoes andvolcanic islands

TrenchOceanic ridge

Oceanic crust Subduction zone

Seafloor spreading

• The formation of the supercontinent Pangaea during the late Paleozoic era and its breakup during the Mesozoic era explain many biogeographic puzzles

By about 10 million yearsago, Earth’s youngestmajor mountain range,the Himalayas, formedas a result of India’scollision with Eurasiaduring the Cenozoic.The continents continueto drift today.

By the end of theMesozoic, Laurasiaand Gondwanaseparated into thepresent-day continents.

By the mid-MesozoicPangaea split intonorthern (Laurasia)and southern(Gondwana)landmasses.

At the end of thePaleozoic, all ofEarth’s landmasseswere joined in thesupercontinentPangaea.

0

65.5

135

251

Mill

ion

s o

f ye

ars

ago

Cen

ozo

icM

eso

zoic

Pal

eozo

ic

North Americ

a

Eurasia

AfricaIndiaSouth

America Madagascar

Australia

Antarctica

Laurasia

Gondwana

Pangaea

Molecular data have provided insights into the deepest branches of the tree of life

Previous Taxonomic Systems

• Early classification systems had two kingdoms: plants and animals

• Robert Whittaker proposed five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia

Plantae Fungi Animalia

Protista

Monera

Eukaryotes

Prokaryotes

Reconstructing the Tree of Life: A Work in Progress

• The five kingdom system has been replaced by three domains: Archaea, Bacteria, and Eukarya

• Each domain has been split into kingdoms

Chapter 27 Chapter 28

Pro

teo

bac

teri

a

Ch

lam

ydia

s

Sp

iro

chet

es

Cya

no

bac

teri

a

Gra

m-p

osi

tive

bac

teri

a

Ko

rarc

hae

ote

s

Eu

ryar

chae

ote

s, c

ren

arch

aeo

tes,

nan

oar

chae

ote

s

Dip

lom

on

ads,

par

abas

alid

s

Eu

gle

no

zoan

s

Alv

eola

tes

(din

ofl

agel

late

s, a

pic

om

ple

xan

s, c

ilia

tes)

Domain Archaea

Universal ancestor

Domain Bacteria

Domain Eukarya

Str

amen

op

iles

(w

ater

mo

lds,

dia

tom

s, g

old

en a

lgae

, b

row

n a

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)

Cer

cozo

ans,

rad

iola

rian

s

Red

alg

ae

Ch

loro

ph

ytes

Ch

aro

ph

ycea

ns

Chapter 29

Bry

op

hyt

es (

mo

sses

, li

verw

ort

s, h

orn

wo

rts)

Plants

Fungi

Animals

Chapter 30 Chapter 28

See

dle

ss v

ascu

lar

pla

nts

(fe

rns)

Gym

no

sper

ms

An

gio

sper

ms

Am

oeb

ozo

ans

(am

oeb

as,

slim

e m

old

s)

Ch

ytri

ds

Chapter 31

Zyg

ote

fu

ng

i

Arb

usc

ula

r m

yco

rrh

izal

fu

ng

i

Chapter 32 Chapters 33, 34

Sac

fu

ng

i

Clu

b f

un

gi

Ch

oan

ofl

agel

late

s

Sp

on

ges

Cn

idar

ian

s (j

elli

es,

cora

l)

Bil

ater

ally

sym

met

rica

l an

imal

s (a

nn

elid

s,ar

thro

po

ds,

mo

llu

scs,

ech

ino

der

ms,

ver

teb

rate

s)

Animations and Videos

• Bozeman - Origin of Life

• Bozeman – Abiogenesis

• Synthesis of Prebiotic Molecules

• Miller Urey Experiment

• Bozeman - Biotic and Abiotic Factors

• Endosymbiosis

• Bozeman – Endosymbiosis

• Evolution of Organelles

Animations and Videos

• The Simplest Eukaryotes

• Pasteur's Experiment

• Bozeman - Classification of Life

• Three Domains

• Bozeman - The Three Domains of Life

• Bozeman – Biodiversity

• Chapter Quiz Questions – 1

• Chapter Quiz Questions – 2

Which of the following taxonomic categories includes the fewest number of species?

• Animalia

• Panthera

• Felidae

• Carnivora

• Mammalia

Which of the following taxonomic categories includes the fewest number of species?

• Animalia

• Panthera

• Felidae

• Carnivora

• Mammalia

Animals that possess homologous structures probably _____.

• evolved from the same ancestor

• are headed for extinction

• by chance had similar mutations in the past

• are not related

• have increased genetic diversity

Animals that possess homologous structures probably _____.

• evolved from the same ancestor

• are headed for extinction

• by chance had similar mutations in the past

• are not related

• have increased genetic diversity

Which of the following would make the most suitable outgroup species for a cladogram relative to all the other species?

• frog

• tuna

• snake

• penguin

• bat

Which of the following would make the most suitable outgroup species for a cladogram relative to all the other species?

• frog

• tuna

• snake

• penguin

• bat

Which principle is not used to identify phylogenetic relationships?

• maximum parsimony

• Occam’s razor

• maximum likelihood

• minimum analogy

Which principle is not used to identify phylogenetic relationships?

• maximum parsimony

• Occam’s razor

• maximum likelihood

• minimum analogy

Given the DNA sequence data in the table, which phylogenetic tree is the most parsimonious?

•

•

•

Given the DNA sequence data in the table, which phylogenetic tree is the most parsimonious?

a)

b)

c)

Which of the following is the correct way to write the scientific name for humans?

• Homo sapiens

• homo sapiens

• Homo sapiens

• homo sapiens

Which of the following is the correct way to write the scientific name for humans?

• Homo sapiens

• homo sapiens

• Homo sapiens

• homo sapiens

When describing a group of animals, you speak about an ancestral species and some but not all of its descendants. This is an example of a

• monophyletic group.

• polyphyletic group.

• paraphyletic group.

When describing a group of animals, you speak about an ancestral species and some but not all of its descendants. This is an example of a

• monophyletic group.

• polyphyletic group.

• paraphyletic group.

Hair on mammals when compared to other vertebrates is an example of a

• shared derived character.

• shared ancestral character.

• paraphyletic character.

• polyphyletic character.

Hair on mammals when compared to other vertebrates is an example of a

• shared derived character.

• shared ancestral character.

• paraphyletic character.

• polyphyletic character.

Which of the following broad taxonomic groups is not one of the three domains of life?

• Bacteria

• Archaea

• Plantae

• Eukarya

Which of the following broad taxonomic groups is not one of the three domains of life?

• Bacteria

• Archaea

• Plantae

• Eukarya

Researchers have long debated different hypotheses for the phylogeny and classification of species in the bear family, Ursidae. In 2008, researchers obtained complete mitochondrial DNA (mtDNA) genome sequences for the eight living species of bears. Based on these data, the researchers constructed a phylogenetic tree for the family Ursidae. (See next slide.)

Scientific Skills Exercise

a)branch point 1

b)branch point 2

c)branch point 3

d)The most recent common ancestor to all living bears is not shown in this tree.

Which branch point represents the most recent common ancestor of all bears?

Which branch point represents the most recent common ancestor of all bears?

a)branch point 1

b)branch point 2

c)branch point 3

d)The most recent common ancestor to all living bears is not shown in this tree.

a) branch point 1

b) branch point 2

c) branch point 3

d) The sloth bear and the spectacled bear do not share a common ancestor.

Which branch point represents the most recent common ancestor of the sloth bear and the spectacled bear?

a) branch point 1

b) branch point 2

c) branch point 3

d) The sloth bear and the spectacled bear do not share a common ancestor.

Which branch point represents the most recent common ancestor of the sloth bear and the spectacled bear?

a) branch point 2

b) branch point 3

c) branch point 4

d) branch point 5

Which branch point represents the most recent common ancestor of the Asian black bear and the brown bear?

a) branch point 2

b) branch point 3

c) branch point 4

d) branch point 5

Which branch point represents the most recent common ancestor of the Asian black bear and the brown bear?

a) the polar bear

b) the spectacled bear

c) the sloth bear

d) the giant panda

Which species is the basal taxon in this tree?

a) the polar bear

b) the spectacled bear

c) the sloth bear

d) the giant panda

Which species is the basal taxon in this tree?

a) the brown bear

b) the ancestor represented by branch point 7

c) the Asian black bear

d) the American black bear

Identify the sister taxon to the polar bear.

a) the brown bear

b) the ancestor represented by branch point 7

c) the Asian black bear

d) the American black bear

Identify the sister taxon to the polar bear.

a) The polar bear

b) The sloth bear

c) The sloth bear and the polar bear are equally distant relatives of the sun bear.

According to this tree, is the sun bear more closely related to the sloth bear or the polar bear?

a) The polar bear

b) The sloth bear

c) The sloth bear and the polar bear are equally distant relatives of the sun bear.

According to this tree, is the sun bear more closely related to the sloth bear or the polar bear?

a) This phylogenetic tree contains homoplasies.

b) This phylogenetic tree is rooted.

c) The Ursidae family is a paraphyletic group.

d) The Ursidae family is a polyphyletic group.

The tree includes the most recent common ancestor of all living species of bears (branch point 1). What does this tell you about this phylogenetic tree?

a) This phylogenetic tree contains homoplasies.

b) This phylogenetic tree is rooted.

c) The Ursidae family is a paraphyletic group.

d) The Ursidae family is a polyphyletic group.

The tree includes the most recent common ancestor of all living species of bears (branch point 1). What does this tell you about this phylogenetic tree?

a) all species of living bears

b) brown bear, polar bear, ancestral species 4, ancestral species 7

c) sun bear, Asian black bear, American black bear, ancestral species 5, ancestral species 6

d) sun bear, sloth bear, spectacled bear

Which of the following groups of species is a monophyletic group, or clade?

a) all species of living bears

b) brown bear, polar bear, ancestral species 4, ancestral species 7

c) sun bear, Asian black bear, American black bear, ancestral species 5, ancestral species 6

d) sun bear, sloth bear, spectacled bear

Which of the following groups of species is a monophyletic group, or clade?