The Origin and Evolution of Life

AP Biology: Chapter 20

Key Concepts:

Life originated more than 3.8 billion years

ago

All of the compounds necessary for life

could have formed spontaneously under

conditions that existed on the early Earth

The history of life spans five intervals of

geologic time

Key Concepts:

Divergence led to two prokaryotic lineages and

to the eukaryotic divergence

A theory of endosymbiosis helps explain the

profusion of specialized organelles

All of the kingdoms are characterized by

persistence, extinctions, and radiations

Certain environmental insults have had

profound impacts on the direction of evolution

Impacts, Issues Video

Looking for Life in All the Odd Places

The Big Bang

12-15 billion years ago

all matter was

compressed into a space

the size of our sun Sudden instantaneous

distribution of matter and energy throughout the known universe

Conditions on the Early Earth

4.5 billion years ago “Cloud” began to condense

Minerals and ice orbiting the sun started clumping together

4 billion years ago Crust and mantle formed

Heavy metals moved to Earth’s interior, lighter ones floated to

surface

Primitive atmosphere H2, N2, CO, CO2 , probably no O2

Hot temperatures

Earth Is “Just Right” for Life

Smaller in diameter, gravity would not be great enough to hold onto atmosphere

Closer to sun, water would have evaporated

Farther from sun, water would have been locked up as ice

Early Earth

Primitive atmosphere

H2

N2

CO

CO2

Probably no free O2

Synthesis of Organic Compounds

Amino acids, other organic compounds can form

spontaneously under conditions like those on early Earth Clay may have served as template for complex

compounds Compounds may have formed near hydrothermal vents

Stanley Miller’s experiment Methane, hydrogen, ammonia and water in a reaction

chamber

Simulated lightning

Amino acids and small organic compounds formed

tovacuumpump

boiling water

sparkdischarge

liquid water in trap

water containingorganic compounds

water droplets

water in

condenser

electrodes

water out

CH4

NH3

H2OH2

gases

Stanley Miller’s Experiment

Emergence of the First Living Cells

Metabolism Natural assembly of enzymes, ATP and other

organic compounds Chemical interactions

enzyme enzyme

A + B -------> C -------> D

Origin of Organic Compounds

Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth

Clay may have served as template for complex compounds

Compounds may have formed near hydrothermal vents

Chemical Evolution

Spontaneous formation of porphyrin rings from formaldehyde

Components of chlorophylls and cytochromes

In energy yielding pathways.

formaldehyde

porphyrin ring system

chlorophyll a

RNA World

DNA is genetic material now

DNA-to-RNA-to-protein system is complicated

RNA may have been first genetic material

RNA can assemble spontaneously

How switch from RNA to DNA might have

occurred is not known

Proto-Cells

Microscopic spheres of proteins or lipids can self assemble

Tiny sacs like cell membranes can form under laboratory conditions that simulate conditions in evaporating tidepools

Nanobes may resemble proto-cells

Emergence of the First Living Cells

Self Replicating Systems RNA

DNA

Plasma Membranes Proto-cells

proteins lipids

livingcells

formation ofprotein-RNA systems,

evolution of DNA

formation oflipid spheres

spontaneous formation of lipids,carbohydrates, amino acids, proteins,nucleotides under abiotic conditions

membrane-bound proto-cells

self-replicating system enclosed in aselectively permeable, protective lipid sphere

DNA RNA enzymes andother proteins

Stepped Art

Proterozoic Eon

Origin of photosynthetic Eubacteria

Noncyclic pathway first

Cyclic pathway next

Oxygen accumulates in atmosphere

Origin of aerobic respiration

The First Cells

Originated in Archeon Eon

Were prokaryotic

heterotrophs

Secured energy through

anaerobic pathways No oxygen present

Relied on glycolysis and

fermentationProkaryotes

Origin of Prokaryotic and Eukaryotic Cells

Advantages of Organelles

Nuclear envelope may have helped to protect genes from competition with foreign DNA

ER channels may have protected vital proteins

DNA

infolding of plasma membrane

Where Did Organelles Come From ?

Membranous enclosures Nucleus ER

Endosymbiosis Mitochondria Chloroplasts Both have self-replicating DNA, divide

independently of cell

Theory of Endosymbiosis Lynn Margulis Mitochondria and chloroplasts are the

descendents of free-living prokaryotic organisms

Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts

A Theory of Life’s Beginnings

Major Events of Life’s History

Life In the Paleozoic Era

Periods Cambrian

Ordovician

Silurian

Devonian

Carboniferous

Permian

All six kingdoms in the seas

Land plants and animals arise

Life in the Paleozoic

Cambrian 550-500 mya Land masses dispersed near equator Simple marine communities Origin of animals with hard parts

Ordovician 500-435 mya Gondwana drifts south Major radiations of marine invertebrates and

fishes

Life in the Paleozoic

Ordovician-Silurian boundary 435 mya First known ice age First known global mass extinction

Silurian and Devonian eras Vascular plants arise Origin of amphibians

Life in the Paleozoic

Silurian swamp Dominated by non-

vascular plants Forerunners of

modern ferns and club mosses

Life in the Paleozoic

Devonian-Carboniferous boundary Sea levels change dramatically Mass extinction

Carboniferous 360-290 mya Radiations of insects, amphibians Origins of reptiles Spore-bearing plants dominant

Life in the Paleozoic

Permian 290-240 mya Radiation of reptiles and gymnosperms

Closed with greatest mass extinction

Land masses collided to form Pangea

More than 50% of families disappeared

Only 5% of known species survived

Life in the Mesozoic Era

Periods Triassic Jurassic Cretaceous

Pangea began to break up Continental drift Divergence and Speciation

Major adaptive radiations

Life in the Mesozoic

Angiosperms arose in the late Jurassic or early Cretaceous.

Adaptive radiation made them dominant plants in land environments

Rise of the Ruling Reptiles

Dinosaurs Arose early in the Triassic

Weren’t dominant until after mass extinction

Adaptive radiation

Two Hypotheses for Dinosaur Extinction Asteroid Impact Theory

Global Broiling Theory

Last Few Seconds of the Cretaceous

Life in the Cenozoic Era

Present era

Geological shift

Shifts in climate

Adaptive radiation of mammals Tropical forests

Woodlands

Grasslands

Species diversity

In Conclusion

The Big Bang is a model of the origin of the

universe

Every element of the solar system and of life

is a product of the physical and chemical

evolution of the universe

Four billion years ago, the Earth formed

The primitive atmosphere consisted of H2, N2 ,

CO, and CO2

In Conclusion

After the crust cooled, water accumulated

and seas developed

Many experiments have yielded indirect

evidence that life originated under conditions

prevalent on the early Earth

Life originated about 3.8 billion years ago

Major changes in the Earth’s crust,

atmosphere, and oceans have influenced life

In Conclusion

Discontinuities in the fossil record mark the time of global mass extinction

The first living cells were prokaryotes Divergence led to the evolution and to

the ancestor of the Archaebacteria and Eukaryotes

Ozygen began to accumulate in the atmosphere during the Proterozoic

In Conclusion

Oxygen in the atmosphere served as a

selective pressure, bringing about the

spontaneous formation of organic molecules

Aerobic respiration was a key step towards

the origin of eukaryotic cells

Mitochondria and chloroplasts probably

evolved as an outcome of endosymbiosis

In Conclusion

Ozone developed as a product of an O2

rich atmosphere.

Ozone protects against ultraviolet

radiation

Many events brought on pulses of mass

extinctions and adaptive radiations