History of Life on EarthHistory of Life on Earth

Chapter 25

Overview

• First Cells

• Major Life events

• Fossil Record

• Geologic Time scale

• Mass extinctions

• Continental Drift

What was Early Earth like?

What do we really know about What do we really know about the first living organism??the first living organism??

Can we take Darwin’s theory all the way back to the Origin of Life?

What were the major milestones in the Evolution of Life?

How long ago was that ?

Getting used to the geologic time scale…

• We use– Millions of years (MYA) and– Billions (BYA) of years ago.

• One Million Years: If we give 10,000 years for all of recorded human history– One million years equals 100 times all

human history.– Enough time for 30,000 generations

Evolutionary Clock

• Eras not to scale• “Our” world, with

plants and animals on land is not very old

• Protists and Bacteria / Archae have been around longer and are more diverse.

Fig 25-UN11

Origin of solar systemand Earth

4

32

1

Paleozoic

Meso-

zoic

Ceno-zoic

Proterozoic ArchaeanBillions of years ago

Geologic Time Scale Table 25.1

Know : • Eons

– Phanerozoic– Proterozoic– Archaean

• 4 eras – Their dates– Major Animal and

Plant groups– “Precambrian” Era

• Periods:– Permian– Cretaceous (K)– Tertiary (T)

The three Eras andthe new groups that begin to

dominate on land• Cenozoic – 65.5 MYA

– Mammals, birds flowering plants

• Mesozoic – 251 MYA– Reptiles, conifers

• Paleozoic – 542 MYA– Amphibians, insects, moss, ferns

• Precambrian (2 eons) – 4.6 BYA – Origin of animal phyla– Protists, bacteria

The three Eons andthe new groups that begin to

dominate on land

Eons:

• Phanerozoic – Present to 542 MYA

“Precambrian”:

• Proterozoic - 542- 2,500 MYA– Origins of Eukaryotes

• Archaean – 2,500- 4,500 MYA– bacteria, and oxygen atmosphere

Four Eras

• Eras do not have same amount of time• Pace of evolution quickens with each

major branch or era .• Recent organisms generally are more

complex – older ones simpler.

• Why ?

Key Events in the History of Life on Earth

• 4.6 BYA Formation of Earth• Origins of Biomolecules• Formation of Polymers• Origin of Protobionts; Self replicating

RNA-DNA; Metabolism; Evolution• 3.5 BYA Formation of first cell –

prokaryotes

Key Events in the History of Life on Earth

• 2.7 BYA Origin of Oxygen generating photosynthesis

• 1.5 BYA Origin of Eukaryote cells

• 1.2 BYA – 565 MYA Multicellularity

• 535 MYA Cambrian Explosion

• 500 MYA Colonization of land

Fig 25-UN8

Millions of years ago (mya)

1.2 bya:First multicellular eukaryotes

2.1 bya:First eukaryotes (single-celled)

3.5 billion years ago (bya):First prokaryotes (single-celled)

535–525 mya:Cambrian explosion(great increasein diversity ofanimal forms)

500 mya:Colonizationof land byfungi, plantsand animals

Pre

sen

t

500

2,00

0

1,50

0

1,00

0

3,00

0

2,50

0

3,50

0

4,00

0

Fig. 25-4Present

Dimetrodon

Coccosteus cuspidatus

Fossilizedstromatolite

Stromatolites Tappania, aunicellulareukaryote

Dickinsoniacostata

Hallucigenia

Casts ofammonites

Rhomaleosaurus victor, a plesiosaur

10

0 m

illi

on

ye

ars

ag

o2

00

17

53

00

27

04

00

37

55

00

52

55

65

60

03

, 500

1, 5

0 0

2.5 cm4.5 cm

1 cm

Fig. 25-10

Sp

on

ge

s

LateProterozoiceon

EarlyPaleozoicera(Cambrianperiod)

Cn

idar

ian

s

An

nel

ids

Bra

ch

iop

od

s

Ec

hin

od

erm

s

Ch

ord

ate

s

Mill

ion

s o

f y

ears

ag

o

500

542

Art

hro

po

ds

Mo

llus

cs

How did Life come into being ?

Spontaneous generation ?

• Life from non-living matter.– Mice from wet hay makes mice

• Refute for animals, and plants in 1600’s.

• Still thought to be the case for microbes, until Pasteur.

Louis Pasteur(1822-1895)

• Disproved spontaneous generation

• Showed that biogenesis alone accounted for new cells

• Invented Pasteurization

Biogenesis

• Life (whole organisms) comes from reproduction of other preexisting life.

• Later, the cell theory will be similar– all cells come from preexisting cells.

What about the first Cell?

• Scientists think, first cell-like structures came from non living matter.

• What would be needed to make a cell from scratch ?

Origin of life -

• Need to have biomolecules:– Complex Carbohydrates– Proteins– Lipids– Nucleic acids

• To make membranes,enzymes, DNA and all the other cellular components.

Where did biomolecules come from?

• Today only living organisms make biomolecules

“Arm Chair” science

• Still mostly untested hypotheses, and conjecture.

• Trying to test hypotheses by making artificial cells in labs.

Conditions on Earth 4 BYAOparin – Haldane 1920’s chemists

• No free Oxygen – No Ozone layer

• More uv radiation

• Reducing (electron rich) atmosphere

• More lightning

• Meteorite bombardment

• More volcanic activity

• H20, Methane (CH4), Ammonia (NH3)

Energy rich early earth

Urey & Miller - 1953

• Used Oparin / Haldane ideas of earth earth conditions

• Made an apparatus to mimic early earth conditions

• Let run and tested fluid for compounds

• Found simple sugars, amino acids, and other organic compounds.

Stanley Miller

Significance:

Abiotic synthesis of macromolecules

Ribozymes

• RNA self replication before enzymes?

• RNA before DNA

Hypothetical Protobionts

Not “facts” but working hypotheses

• Lab experiments can only show what could have happened

• Other thoughts:– Deep sea vents – constant environment,

chemical energy– Panspermia or microbes from

meteorites

• Most like our understanding will change greatly in future.

Universal Common Ancestor

• Hypothetical• Would be cell from which all modern life

has descended• Have things that ALL living organisms

share:– Phospholipid bilayer cell membrane– Use DNA/ RNA for genes, and make proteins

from the genetic code– Glycolysis, ATP in their metabolism

Fossil Record• Fossil any preserved remnant or

impression of an organism that lived in the past

• Most form in sedimentary rock, from organisms buried in deposits of sand and silt. Compressed by other layers.

• Also includes impressions in mud

• Most organic matter replaced with minerals by Petrification

• Some fossils may retain organic matter• Encased in ice, amber, peat, or dehydrated• Pollen

Fossil Formation –

Radiometric “absolute” dating

Dating Fossils

• “Absolute” Radiometric dating: decay and half-life of natural isotopes.

• Index dating – comparing index fossils in strata

Brachiopod index fossils

Many changes in geologic history due to Plate tectonics

Layers of the EarthLayers of the Earth

Mantle

Core

Crust

Low-velocity zone

Solid

Outer core(liquid)

Innercore(solid)

35 km (21 mi.) avg., 1,200˚C

2,900km(1,800 mi.)3,700˚C

5,200 km (3,100 mi.), 4,300˚C

10 to 65km

100 km

200 km

100 km (60 mi.)200 km (120 mi.)

Crust

Lithosphere

Asthenosphere(depth unknown)

Plate tectonics• The study of the movement of earth

structures in the crust.

• Internal forces from the core create heat that keeps asthenosphere molten.– Convection cells – Mantle Plumes

Convection Cell in Mantle

Earth’s Layers - Crust

• Oceanic Crust – only 3 miles thick

• Continental Crust – up to 12-40 miles thick

• Oceans change shape much more than continents.

• These land movements we call Plate Tectonics, and cause earthquakes.

Plate tectonics- Divergent

Areas

• Plates spread apart in Divergent (constructive) making new crust

Convergent zones

• Plates move together and collide.

• An Oceanic Plate sinks under Continental in a Subduction zone. – Causes Earthquakes, volcanoes

• When Continental plates collide neither subducts, both deform, mountains

Convergent plates

Slide 8

Fig. 10.6b, p. 215

Lithosphere

Trench Volcanic island arc

Asthenosphere

Risingmagma

Subductionzone

Trench and volcanic island arc at a convergentplate boundary

Fig. 25-12

(a) Cutaway view of Earth (b) Major continental plates

Innercore

Outercore

Crust

MantlePacificPlate

NazcaPlate

Juan de FucaPlate

Cocos Plate

CaribbeanPlate

ArabianPlate

AfricanPlate

Scotia Plate

NorthAmericanPlate

SouthAmericanPlate

AntarcticPlate

AustralianPlate

PhilippinePlate

IndianPlate

Eurasian Plate

Fig. 25-12b

(b) Major continental plates

PacificPlate

NazcaPlate

Juan de FucaPlate

Cocos Plate

CaribbeanPlate

ArabianPlate

AfricanPlate

Scotia Plate

NorthAmericanPlate

SouthAmericanPlate

AntarcticPlate

AustralianPlate

PhilippinePlate

IndianPlate

Eurasian Plate

Fig. 25-13

SouthAmerica

Pangaea

Mil

lio

ns

of

year

s ag

o

65.5

135

Mes

ozo

ic

251

Pal

eozo

ic

Gondwana

Laurasia

Eurasia

IndiaAfrica

AntarcticaAustralia

North Americ

a

Madagascar

Cen

ozo

ic

Present

• 10 MYA India (previously an island) hits Asia

• 50 MYA. Australia becomes completely isolated

• 65.5 MYA NA and Europe still touched

• 135 MYA Pangea broke up into Laurasia and Gondwanaland

• 251 MYA Pangea all land masses touched

Mass extinctions

• Mark borders of Eras: – 251 Permian (Paleo-Mesozoic)– 65.5 Cretaceous (K/T boundary; Meso-

Cenozoic)

• Caused by a major change that affects many species at once.

Fig. 25-14

To

tal e

xtin

cti

on

ra

te(f

amili

es

pe

r m

illio

n y

ears

):

Time (millions of years ago)

Nu

mb

er o

f fa

mili

es:

CenozoicMesozoicPaleozoicE O S D C P Tr J

542

0

488 444 416 359 299 251 200 145

EraPeriod

5

C P N

65.5

0

0

200

100

300

400

500

600

700

800

15

10

20

Fig. 25-16

Pre

dat

or

gen

era

(pe

rcen

tag

e o

f m

arin

e g

en

era

)

Time (millions of years ago)

CenozoicMesozoicPaleozoicE O S D C P Tr J

542

0

488 444 416 359 299 251 200 145

EraPeriod C P N

65.5 0

10

20

30

40

50

Permian Mass Extinction

• 90% marine & 80% insect species gone • 251 MYA• Took place in about 5 MY • 2 Possible causes:

– Pangaea forming– Extreme volcanism- Global warming, climate change.

• Drop in sea level, loss of shoreline & intertidal, • More severe continental weather• Isolated species come together and compete,

causing extinctions• Paleozoic to Mesozoic boundary

Cretaceous extinctions• 65.5 MYA • Wiped out 50 % marine species, on land

many families of plants and the Dinosaurs. • Mesozoic to Cenozoic boundary.• Climate cooled and shallow seas

retreated.• Mammals and angiosperms around earlier,

but survived and radiated out to dominant now empty niches

• Many diverse lineages from algae to dinosaurs disappeared at once.

Fig. 25-15

NORTHAMERICA

ChicxulubcraterYucatán

Peninsula

Alvarez-Impact theory

Chicxulub Crater- sonar image

Impact hypothesis• Anomalous Iridium layer marks boundary

layer – element common in meteorites• Chicxulub Crater • Explains large water scarring in NA. • Global winter lasting years, collapsed food

chains. Ignite tremendous wildfires, acid rain.

• Some lineages were dying out before impact.

• Probably a final and sudden blow coming at a time of change, with continental drift, climate change.

Conditions that favor fossilization:

• Having Hard parts – shells, bones,cysts• Get buried, trapped

– Marine species– Marsh, flooding areas

• Abundant species (with many individuals)• Long lived species (as a species)• Avoid eroding away• Get discovered

Limitations of Fossils record

• Has to die in right place under the right conditions. Most things don’t get into the fossil record

• Biased: Highly favors hard parts, abundant, long lived species organisms.

• Lots of missing organisms• Hard to find, only certain areas highly

researched (NA. Europe)

Earth’s history as

a clock

Major events

• Origin of prokaryote cell

• Formation oxygen atmosphere

• Origin of eukaryote cell

• Multi-Origins of multicellularity

• Cambrian explosion of animal phyla

What we do know:

• Earth is old, about 4.6 BYA

• Oldest fossils appear to be filamentous bacteria at about 3.5 BYA.– Formed layers like today’s stromatolites

• Bacteria predated eukaryotes

Early Prokaryote

Fossils

Figure 26.4

Endosymbiosis Fig. 26.13

Endosymbiosis Theory

• Descendant of Archae develops eukaryote type membrane system and nucleus

• Eukaryote cell engulfs bacteria that survive in the cell and develop into plastids and mitochondria

• We’ll review evidence later in eukaryote chapter.

• 2.1 BYA

Endosymbiosis –membrane layers

Coral

• Living example of endosymbiotic relationships

Earliest Multicellular organisms

• 1.5 MYA

Cambrian Explosion

• Most animal appear at same time phyla in 20 MY

• Long fuse- began earlier

Systematics

• Taxonomy is naming, & organizing organisms, both living and dead, into groups.

• Systematics, use evolutionary relationships as the classification hierarchies.

Systematics debates:

• Biggest debates, and changes will be at higher levels of classification.

• Shows scientists interest levels.– Most lower level groups figured out.– Question the origins of these groups– Rely heavily on comparative gene

sequences.

Debates in Evolution

• Most lay people think the big debate is around the origins of humans from apes.

• Most scientists see this area as pretty clear, with details to be worked out by specialists.

• Origins of Domains, Kingdoms the big questions in evolutionary science today.

Five Kingdoms

A Changing View of Diversity

Prokaryote Diversity

Eukaryote Diversity

Fig. 25-6

Very late cynodont (195 mya)

Later cynodont (220 mya)

Early cynodont (260 mya)

Therapsid (280 mya)

Synapsid (300 mya)

Temporalfenestra

Temporalfenestra

Temporalfenestra

EARLYTETRAPODS

Articular

Key

Quadrate

Dentary

Squamosal

Reptiles(includingdinosaurs and birds)

Dimetrodon

Very late cynodonts

Mammals

Sy

na

ps

ids

Th

era

ps

ids

Ea

rli er c

yn

od

on

ts

Fig. 25-7

Animals

Colonizationof land

Paleozoic

Meso-

zoic

Humans

Ceno-zoic

Origin of solarsystem andEarth

ProkaryotesProterozoic Archaean

Billions of years ago

1 4

32

Multicellulareukaryotes

Single-celledeukaryotes

Atmosphericoxygen

Fig. 25-17

Millions of years ago

Monotremes(5 species)

250 150 100200 50

ANCESTRALCYNODONT

0

Marsupials(324 species)

Eutherians(placentalmammals;5,010 species)

Ancestralmammal

Fig. 25-18

Close North American relative,the tarweed Carlquistia muirii

Argyroxiphium sandwicense

Dubautia linearisDubautia scabra

Dubautia waialealae

Dubautia laxa

HAWAII0.4

millionyears

OAHU3.7

millionyears

KAUAI5.1

millionyears

1.3millionyears

MOLOKAIMAUI

LANAI

Fig. 25-18a

HAWAII0.4

millionyears

OAHU3.7

millionyears

KAUAI5.1

millionyears

1.3millionyears

MOLOKAIMAUI

LANAI

Fig. 25-19

(a) Differential growth rates in a human

(b) Comparison of chimpanzee and human skull growth

NewbornAge (years)

Adult1552

Chimpanzee fetus Chimpanzee adult

Human fetus Human adult

Fig. 25-19a

(a) Differential growth rates in a human

NewbornAge (years)

Adult1552

Fig. 25-19b

(b) Comparison of chimpanzee and human skull growth

Chimpanzee fetus Chimpanzee adult

Human fetus Human adult

Fig. 25-20

Gills

Fig. 25-21

Vertebrates (with jaws)with four Hox clusters

Hypothetical earlyvertebrates (jawless)with two Hox clusters

Hypothetical vertebrateancestor (invertebrate)with a single Hox cluster

Second Hox duplication

First Hox duplication

Fig. 25-22

Hox gene 6 Hox gene 7 Hox gene 8

About 400 mya

Drosophila Artemia

Ubx

Fig 25-UN9

Origin of solar systemand Earth

4

32

1

PaleozoicMeso-

zoicCeno-zoic

Proterozoic Archaean

Billions of years ago

Fig 25-UN10

Flies andfleas

Moths andbutterflies

Caddisflies

Herbivory