Evolution A Change through time. Evolution defined for our purposes The theory that life arose by...

Evolution

A Change through time

Evolution defined for our purposes

The theory that life arose by natural processes at an early stage of the earth’s history and that complex organisms developed from simple organisms by a process of gradual change.

Lamarckism The first scientific explanation of evolution

Jean Baptiste de Lamarck was the first to publish the idea that fossils were the remains of extinct animals (1809)

His theory was that organisms strived to adapt to their environment, acquired adaptations and pass them on to their offspring.

The giraffe got a long neck from stretching for food

The snake lost its legs because they got in the way in dense vegetation

A man who exercised a lot would pass his strength on to his sons.

Unsurprisingly this has been disproved by geneticists as there is no genetic evidence to support the theory.

Fossils

The use of fossils as evidence was still accepted and is now considered the strongest evidence for evolution.

A fossil is the remains of or an imprint of past life uncovered from the crust of the Earth.

Biased because of selective preservation.

Fossils – Methods of fossilization

1. Preservation in Amber Amber is a sticky gum-like

resin from trees that hardens into a transparent yellow material.

Organisms can be trapped and embedded in the resin before it hardens.

2. Preservation in ice In Arctic regions,

organisms could be preserved for thousands of years from the last ice age.

The 25000 year old wooly mammoth was found with skin and hair intact.

Fossils Fossils – Methods of fossilization– Methods of fossilization

3. Preserved hard parts After the soft tissues are

decomposed by oxidation, bacterial action and fungi, the hard materials were easily buried under water borne sediments or tar and preserved

4. Petrification If the organisms body lies

in water that is rich in minerals, the minerals permeate the body and when the water evaporates, the minerals remain in the shape of the organism – like turning the body to stone.

5. Molds & Casts If the organisms body

lies in water and sand is washed over the body burying it.

The sand hardens to rock and after the body decomposes, the sand “mold” remains

6. Imprints Impressions in mud or tar stay after

the mud hardens. Like a foot print in cement.

Evidence of Evolution1. Comparative

Anatomy

Comparative Anatomy is the study of structural similarities and differences between organisms

Evidence of EvolutionEvidence of Evolution1. Comparative 1. Comparative

AnatomyAnatomyA. Homologous Structures – similar

structures and similar embryonic development but different forms and functions- indicates evolutionary relationship

AnatomyAnatomyB. Analogous Structure – similar

external forms and function but quite different internally- indicates no evolutionary relationship

AnatomyAnatomyC. Vestigial

Structures - Remnants of structures that were functional in an ancestral form. - Tend to be reduced in size and serve little or no function.

EmbryologyEmbryology Comparisons of patterns of

development Closely related

organisms show similar patterns of development.

EmbryologyEmbryologyThe more closely related the organisms,the longer they resemble one another during development.

By comparing gene and base sequences, we can identify links between organisms.

The more DNA in common, the more closely related the organisms.

Evidence of EvolutionEvidence of Evolution3. Comparative DNA3. Comparative DNA

For example: The haemoglobin gene for humans is only one base pair different from that of the haemoglobin gene for a gorilla while the haemoglobin gene for a horse has 24 different base pairs.

Evidence of EvolutionEvidence of Evolution3. Comparative DNA3. Comparative DNA

Evidence of EvolutionEvidence of Evolution4. Geographic 4. Geographic

DistributionDistribution Pangaea - 165mya the continents

split Migration and continental shift. Animals and native

flowering plants of west coast US are closely related to those on east coast Asia.

Similar organisms in Africa and South America

Evidence of EvolutionEvidence of Evolution5. Fossil record5. Fossil record

Fossils give us snapshot of many organisms that have inhabited the earth.

To study and understand the information provided by fossils, scientists can compare body structures of different fossilized organisms with other fossils and with organisms living today.

To put the life of the organism in perspective, the fossil must be dated to provide a time-frame for its life.

Evidence of EvolutionEvidence of Evolution5. Fossil Record - 5. Fossil Record -

DatingDatingA. Relative dating

- if the rock layers are in the original order of deposit, then the lower the layer, the older the deposit and any fossil found in it.

DatingDatingB. Correlation –

shows that certain rock layers in one place are older than certain rock layers in another place.

DatingDatingC. Index Fossils

- fossils that allow relative dating of rocks within a fairly narrow time span. If you find a certain fossil of an organism in one region that matches the fossils found in another region, the rocks and other fossils are likely from the same time period.

DatingDatingD. Radioactive dating – most reliable

The chemistry involved: Atoms are made of protons,

electrons and neutrons Isotopes are atoms having different

atomic weight because of differing numbers of neutrons.

DatingDatingCarbon always has 6 protons Carbon has an average atomic mass of

12.01. It could have a mass of 12, 13 or 14 as it could have 6, 7 or 8 neutrons

C12 has 6 protons and 6 neutrons so a mass of 12.

C14 is unstable so it decays over time and can be used for dating.

DatingDating C14 is found in the atmosphere and

is absorbed by living things. After an organism dies, the C14

slowly decays into nitrogen. If we measure the amount of C14

that remains in the organism, we can determine how long ago it died using the half-life of the C14.

DatingDatingHalf Life – The time required for half

of the nuclei in a given sample of a radioactive isotope to decay is called its half life. This rate is constant.

C14 decays into nitrogen with a half life of approximately 5730 years.

DatingDatingHalf-life of Carbon 14

0 10000 20000 30000 40000 50000

Time (years)

0 10000 20000 30000 40000 50000

Time (years)

0 10000 20000 30000 40000 50000

Time (years)

0 10000 20000 30000 40000 50000

Time (years)

0 10000 20000 30000 40000 50000

Time (years)

0 10000 20000 30000 40000 50000

Time (years)

0 10000 20000 30000 40000 50000

Time (years)

0 10000 20000 30000 40000 50000

Time (years)

DatingDatingHow old would a fossil containing 20% C14 be? Half-life of Carbon 14

0 10000 20000 30000 40000 50000

Time (years)

From the graph it appears to be about 13000 years old.

DatingDating

A more precise answer can be found by using exponential decay.

y = ( ½ ) n % Carbon # of half-lives

and, time = # of half-lives (n) x 5730

DatingDatingHow old would a fossil containing 20% C14 be?

y = ( ½ ) n

0.20 = ( ½ ) n

Log0.5 0.20 = n

Log 0.20 = n Log 0.5

n = 2.32

time = 2.32 x 5730time = 13 305 years

DatingDating

How much radioactive carbon would be left in a 44 000 year old fossil? Half-life of Carbon 14

0 10000 20000 30000 40000 50000

Time (years)

This would be difficult to find from the graph

DatingDatingHow much radioactive carbon would be left in a 44 000 year old fossil? y = ( ½ ) n

y = ( ½ ) 7.68

n = 7.68

time = n x 5730

44 000 = n x 5730

y = 0.00488

0.488% of the carbon would remain.

DatingDatingAfter how many years is less than one percent of the C14 left in a fossil?y = ( ½ ) n

0.01 = ( ½ ) n

Log0.5 0.01 = n

Log 0.01 = n Log 0.5

n = 6.64

time = 6.64 x 5730time = 38 069 years

DatingDatingIf a specimen was found to be 1.72 million years old, how much C14 remains in the bones?

y = ( ½ ) n

y = ( ½ ) 296.68

n = 296.68

time = n x 5730

1.72 x 106 = n x 5730

y = 4.9 x 10-

90 This amount of carbon is too insignificant!

DatingDating

For any specimen that is over 50 000 years old, it is more practical to use other radioactive compounds to date the fossils.

Uranium has a half life of 710 million years

Potassium has a half life of 1.3 billion years

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