The History of Life on Earth

The History of Life on EarthThe history of life is divided up into eons, eras, periods, and epochs:

Formation of the earth 4600 mya

Oldest known microfossils found in 3500 million year old chert in Western Australia

Oxygen produced by plants accumulates in

the atmosphere

Precambrian Eon

Millions of years ago

Quaternary

Millions of years ago

Eras

Evolutionary History 1Based on fossil evidence and

radio-isotope dating, the

evolutionary history of

plants, fungi, bacteria,

protists, and non-chordate

animals can be compiled.

Bacteria, protists, and fungi have an

evolutionary history extending back

to the Precambrian.

Some invertebrate groups extend

back to the Cambrian Period, but

land plants only as far back as the

Devonian Period.Millions of years ago

Echinoderms

Arachnids

Diplopoda

Crustacea

Insecta

Annelid worms

Molluscks

Flatworms

Cnidarians

Angiosperms

Cycads

Conifers

Sphenophytes (ferns etc)

Fungi

Protists

Bacteria and algae

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Evolutionary History 2

Similarly, the evolutionary

history of chordates can

be traced back to the

Cambrian, but most

animal groups are much

more recent than this.

Placentals

Marsupials

Monotremes

Birds

Squamata (lizards & snakes)

Rhyncocephalia (tuatara)

Crocodilia

Chelonia (turtles a& tortoises)

Amphibians

Lungfish

Ray finned fishes

Sharks and rays

Tunicates

Agnatha (jawless fishes)

Millions of years ago

Mammals

Birds

Reptiles

Amphibians

Fish

Precambrian Life4600 mya: Origin of Earth.

4600–3800 mya: Chemical

and molecular evolution

leading to origin of life:

protocells to anaerobic

bacteria.

3800–2500 mya: Origin of

photosynthetic bacteria.

2500–570 mya: Origin of

protists, fungi, algae, and

animals.

Protozoans

Cnidarians

Algae

Bacteria

Early Paleozoic Life

550-500 mya: Origin of animals with

hard parts, which appear as fossils in

sedimentary rocks.

Simple marine communities become

established.

The Burgess Shale deposits in

Canada contain a rich collection of

early Cambrian fossils.

The fauna (pictured) was strange

and, at first, wrongly

interpreted.

Anomalocaris

Aysheaia

Ottoia

Hallucigenia

WiwaxiaPikaia

Late Paleozoic Life

500-435 mya: Major adaptive

radiations of marine

invertebrates and early fishes.

435-280 mya: Vast swamps with

the first vascular plants. Origin

and adaptive radiation of reptiles,

insects, and spore bearing plants

(including gymnosperms).

240 mya: Mass extinction of

nearly all species on land and in

the sea (the Permian extinction).

Early amphibians

Early vascular plants

Ammonite

Trilobite

Armored fish

Dimetrodon

Early insects

Early gymnosperms

Mesozoic Life240-205 mya:

Recovery of surviving taxa and adaptive radiation of marine invertebrates, dinosaurs, and fishes. Origin of mammals. Gymnosperms become dominant land plants.181-135 mya:

Major radiations of dinosaurs. 135-65 mya:

Major radiations of dinosaurs, fishes, and insects. Origin of angiosperms. 65 mya:

Asteroid impact linked to the mass extinction of many marine species and all dinosaurs (Cretaceous extinction).

Early mammals

Apatosaurus

Styracosaurus

Velociraptor

Icthyosaurus

Indricotherium

Cenozoic Life

65-1.65 mya: Major shifts in climate. Major adaptive radiations of angiosperms (flowering plants), insects, birds and mammals.

3-5 mya: Early humans arise from ape ancestors.

1.65 mya: Modern humans evolve and their hunting and other activities accelerate.

Dryopithecus Sabretooth Tiger

Platybelodon

Diatryma

Glyptodon

Mass Extinctions• Present day — the Holocene extinction event

– predict that humanity's destruction of the biosphere could cause the extinction of one-half of all species in the next 100 years.

• 65 MY ago — at the Cretaceous-Paleocene transition• about 50% of all genera became extinct (75% species). Largest

extinction• 200 MY ago — at the Triassic-Jurassic transition • about 20% of all marine families & the last of the large amphibians

were eliminated• 251 MY ago — at the Permian-Triassic transition• killed 53% of marine families• 444 MY ago — at the Ordovician-Silurian transition • second largest of the five major extinctions in Earth's history in terms

of percentage of genera that went extinct.

What is Evolution?

Microevolution describes the

small-scale changes within

gene pools over generations.

Macroevolution is the term

used to describe large scale

changes in form, as viewed in

the fossil record, involving

whole groups of species and

genera.

KingdomPhylumClassOrderFamilyGenus

Species

Macroevolution includes:Adaptive radiation of groups of species from a common

ancestor into different environments and different niches. Eg. Birds – beaks, feet, diets, etc

The origin of evolutionary novelties such as the wings and feathers of birds, and the upright posture of humans.

The evolutionary history of a species or taxonomic group is called its phylogeny. Classification of species aims to accurately reflect their phylogeny.

Evolution refers to the permanent genetic

change (change in gene frequencies) in

population of individuals. It does not refer

to changes occurring to individuals within

their own lifetimes. Populations evolve, not

individuals.

Microevolution describes the small-scale

changes within gene pools over

generations.

Macroevolution is the term used to

describe large scale changes in form, as

viewed in the fossil record, involving whole

groups of species and genera.

Evidence For Evolution - Fossil

Fossils are preserved remains, impressions or traces of organisms found in rocks.

They provide direct evidence of past life on Earth

Fossil fishTypes of Fossils

Bird bones preserved in a tar

pit

A layer of shell still covers the stone interior of this ammonite

Trilobites preserved in

sedimentary rock

The term fossil refers to any parts or

impressions of an organism that may

survive after its death.

Fossils form best when organisms are buried

quickly in conditions that slow the process

of decay.

Fossils are most commonly found in

sedimentary rock.

Mineral-rich hard parts (bones, teeth, shells) may

remain as fossils, or minerals dissolved in

water, may seep into tissues and replace

the organic matter of the organism.

On rare occasions, fossils retain organic material, as when plant material is

compressed between layers of shale or

sandstone.

Evidence of evolution through fossils

• Fossil is the preserved evidence of life from the past.

• Direct evidence or Indirect evidence

• Direct Evidence

• Fossilised bones (which are actually rock), mould and cast.

Cast

Evidence of evolution through fossils

• Indirect Evidence

• Anything from life from the past, but not direct. Eg paintings, footprints, droppings, tools.

How Fossils Form

• Fossils form in sedimentary rock (rock made from sand or silt or mud).

• These form layers at the bottom of a lake or ocean or river. These layers get compressed and as this happens the sediments get hot, the sand then fuses to form new rock.

• It’s in those sedimentary rocks that fossil form. Almost always under water.

Fossilised Bones

Fossils Forming

• For a fossil to happen, there are three main conditions necessary.

• 1. Once the specimen dies, it needs to be covered very quickly by sediment (usually under water).

• 2. The decay of that organism needs to be prohibited by the exclusion of oxygen by the sediments. Best when conditions are dry, cold or acidic. When sediments are packed around that organism, it stops bacteria from getting to it.

• 3. Must be left undisturbed for millions of years.

What Fossil Records Show Us

• 1. Species disappear over time. Eg dinosaurs.

• 2. That some species weren’t around, but now are. Eg. humans, previous to 2.5 million years ago there have been no fossilised evidence of humans.

• 3. Trend towards complexity as we go from older rocks to younger rocks. Eg. Bacteria-eukaryotes, Fern-flowering plants, reptiles-birds.

What Fossil Records Show Us

• 4. Fossils, which are those that are half way between reptiles and birds. Most classic example is a reptile/bird called archaeopteryx.

Reptile/Bird Archaeopteryx

Problems With Fossils

• Fossil records are not quite complete. Some species are not well represented and most fossils are incomplete.

• COMMON EXAM QUESTION!• Most animals that die do not get fossilised,

they just decay.• Forming fossils is very rare. • Lots of environments aren’t conducive to

making fossils. Eg Mountain Goats

Problems With Fossils

• Fossils get destroyed easy, by movement of sediment.

• Some species have behaviours that aren’t conducive to forming fossils. Eg apes

• Soft bodies. Eg worms

• On the planet for a short period of time.

• Evolved and then become extinct.

• Not very wide spread. Eg cheetahs

Fossils

Fossilisation of organisms occurs when they are entombed in sediments, hardened into rocks, or sometimes trapped in amber.

Types of Fossils include: Mineralisation Imprint or mould Encased in amber or ice

Fossil Record

The fossil record is not a complete record of all past life because the chances of fossils forming is small. Often only hard parts of organisms are preserved and only under certain environmental conditions.

The fossil record is biased in favour of organisms that live in shallow-water sediments.

How old?

Fossils in a Rock Profile

Layers of sedimentary rock are

arranged in the order in which they

were deposited, with the most recent

layers nearer the surface.

Sedimentary layers can be

disturbed by subsequent tectonic

activity.

The interpretation of rock layers

containing fossils allows us to arrange

the fossils in chronological order

(order of occurrence), but does not

give their absolute date.

Only primitive fossils are found in older sediments

New fossil types mark changes in environment

Fossil types differ in each sedimentary rock layer

Numerous extinct species

Recent fossils are found in recent sedimentsMost recent

sediments

Oldest sediments

The Fossil RecordThe fossil record is a substantial, but incomplete, record of

evolutionary history:

Modern species can be traced through fossil relatives to

distant origins.

Fossil species are often similar to, but usually differ from,

today's species.

Fossil types often differ between

sedimentary rock layers.

Numerous extinct species are found as fossils.

Fossils can be dated to establish their approximate absolute

age.

New fossil types mark changes in the past environmental

conditions on the Earth.

Rates of evolution can vary, with bursts of species formation

followed by stable periods.

These fossil teeth, from Mastodon, an extinct elephant, are similar to the

deciduous teeth of modern elephants.

Dating methods

Stratigraphy –relative age of stratum

Dating the fossil recordVarious dating techniques are

available to estimate the relative and absolute age of the rock and the fossils.

1. Stratigraphy – comparison of rock strata, older layers are laid down first so relative ages can be established. Similar fossils in similar rocks will be the same age.

Only primitive fossils are found in older sediments

New fossil types mark changes in environment

Fossil types differ in each sedimentary rock layer

Numerous extinct species

Recent fossils are found in recent sedimentsMost recent

sediments

Oldest sediments

2. Indicator fossils – these are usually widespread, common at a particular time and can be used to date the rock strata of an new fossil discovery.

Graptolites are indicator fossils of the Ordovician period.

3. Absolute dating - is used to determine with accuracy the actual age of the rock or fossil. These techniques measure the decay rate (half-life) of radioactive isotopes. The half-life of an isotope is the time taken for half of the atoms in the radioactive sample to decay (undergo chemical change).

Radiocarbon dating measures the ration of C14 to C12. It is limited to dating fossils less than 50000 years old. (Half life is 5730 years)

Potassium-argon dating K40:Ar40 will date to 4600 million years (Half life is 1250 million years)

Uranium –lead dating U238:Pb207 will date to 4600 million years (Half life is 4.47 billion years)

And there are many more methods as well – tree rings, varve, paleomagnetism, etc.

Macroevolution includes:

Adaptive radiation of

groups of species into

different environments and

different niches.

The origin of evolutionary

novelties such as the

wings and feathers of birds,

and the upright posture of

humans.

The evolutionary history of

a species or taxonomic group

is called its phylogeny.

Evolutionary theory is now supported by a

wealth of observations and experiments. Although biologists do not

always agree on the mechanisms by which populations evolve, the

fact that evolution has taken place is well documented.

Evidence for evolution comes from many sources:

Paleontology: The identification,

interpretation and dating of fossils

gives us some of the most direct

evidence of evolution.

Embryology and evolutionary developmental

biology: The study of embryonic development

in different organisms and its genetic control.

Comparative anatomy:

The study of the morphology of different species. Comparative anatomy

Paleontology

Biogeography: The study of geographic

distributions can indicate where species may

have originally arisen.

Artificial selection: Selective breeding of

plants and animals has shown that the

phenotypic characteristics of species can

change over generations as particular traits are

selected in offspring.

Biochemistry: Similarities and differences in

the biochemical make-up of organisms can

closely parallel similarities and differences in

appearance.

Molecular genetics: Sequencing of DNA and

proteins indicates the degree

of relatedness between organisms.

From gray wolf to Yorkshire terrier:

selective breeding can result in phenotypic

change

Embryonic Development

• By examining the embryonic development of a species and comparing them with other species you can see remarkable similarity. This gives rise to another example of evidence for evolution

Vestigial Structures

• In evolution some animals that have evolved from a common ancestor will share similar organs but in one, the function of that organ may become not needed.

• Humans have muscles in their ears that are the same that a dog uses to wiggles an ear. We no longer need it, it becomes obsolete

Vestigial Structures

• A structure found in a species, which is not being used as it is in other species.

• A structure that is left over from the past, which was once useful, but no longer is.

Vestigial Structures

• Eg pelvis of whales.

• The use of a pelvis is to support our spine on top of our legs so we can walk.

Vestigial Structures

Biogeography

• This is the study of the distribution of organisms. Distribution patterns give clues to the evolutionary history of organism and of the Earth itself.

Biogeographical Evidence for Evolution

• Biogeography is the study

• of the distribution of

• animals and plants

• across the earth.

Progression

• 250 million years ago, all the continents of the earth were joined in one land mass called Pangaea.

• 11 o’clock pm, Pangaea broke up to form Gondwana in the south and Laurasia in the north.

• At about 11.12pm, Africa separated from the rest of Gondwana and then the rest of Gondwana continued to break up until 11.39pm.

Examples of the Effects

• Large, flightless birds (Ratites), only seen in the south.

• Waratahs only seen in Western Australia, closely related to the Proteas of South Africa.

• Mistletoe only native in the north (northern America and across Europe.

• Wattles only seen in Australia and Africa.

DNA evidence

• The similarity of genetic linkage groups between species provides evidence that the species have common ancestry.

• Molecular hybridization is when a single strand of DNA is brought together with a complementary strand. IF done with two different species the level of compatibility shows the closeness of the relationship

Chimpanzee

Percentage differences – 2.4

GIBBON percentage difference from human5.3

Green Monkey percentage difference is 9.5

DNA-DNA hybridisation

• Can be used to compare the DNA sequences of 2 species.

• Denature DNA from 2 species then hybridise them together.

• They will join where they have similar sequences and where they are different they won’t join up.

• Level of similarity is measure by reheating the hybrid molecule.

• The more similarities the more you need to heat it.• A drop in 2 degrees Celsius from the control

indicates a 2% difference in DNA, a 3 degree a 3% etc.

Human and Primate DNA-DNA Comparison

• Chimpanzee: 2.4% difference

• Gibbon: 5.3% difference

• Green monkey: 9.5% difference

• Capuchin monkey: 15.8% difference

Sources of DNA

• Nuclear DNA

• Mitochondrial DNA

• Chloroplast DNA

• Ribosomal RNA

Phylogenetic tree

• A phylogenetic tree is a diagram which is based on homologous features and shows how organisms are related and diverged in evolution

Phylogeny and Taxonomy

Similarity of form due to a shared ancestry is called homology.

EXAMPLE: Classification and phylogeny of Order Carnivora.

Cheetah

Acinonyx

Tiger

Panthera

Felidae

LionPumaCat

Felis

Carnivora

Fox

Vuples

Canidae

Canis

CoyoteWolf

Family(The dog family)

Genus

Order

NOTE: This is a simplified diagram: there are additional families, genera, and species not represented here.

Dog

(The cat family)

Evidence for Evolution – Comparative anatomy

Features of organisms that have a fundamental similarity of structure are called homologous features.

They are evidence for evolutionary relationships. Humans, Birds, bat and Seal have very similar forearm structures therefore they have a common evolutionary ancestor.

Anatomical Evidence of Evolution

Two main kinds of evidence of evolution from anatomy: homologous structures and analogous structures.

But there is also vestigial structures.

Homologous Structures

When species share a common ancestor, so have similar structures, even though they may be used for completely different things.

Example: pentadactyl limb of vertebrates. In our arm we have one upper arm bone, then two

lower arm bones, then we have our wrist bones or carpals, then five fingers (phalanges).

When you look at other mammals, you find this same basic design, even though some may use them for different means.

Homologous Structures

A dog has the same basic design, but they use them for walking on.

A bat uses their fingers to hold out a membrane that they use to fly with.

Whales have the same basic structure in their flippers to swim.

Pentadactyl Limb

Homologous Structures

Different functions but same basic structure. All evolved from the same common ancestor. Kind of evolution that leads to homology is

called divergent evolution (process where by organisms with a recent common ancestor develop different adaptations in different habitats).

Homologous features

Homologous Features are evidence of divergent evolution – splitting off a common ancestral species into two new different species.

Finches of Galapagos Islands are examples of the outcome of divergent evolution. Natural Selection has resulted in different beak characteristics between species as each one became adapted to a particular food.

Analogous Features

Analogous features in different organisms have the same function but have evolved independently. They are evidence of convergent and parallel evolution

Analogous Structures

Features of different species, which have the same basic function, but completely different structure.

Have not been derived from a common ancestor.

Have evolved in response to a similar environment.

Analogous Structures

Eg sharks dorsal fin and dolphins dorsal fin. They are not closely related, but both have dorsal fin.

Analogous Structures Eg the wings of a pterosaurs, bat and bird