Download Evidence of evolution from the past.

Evidence of evolution from the
past.
• Fossil records
• Biogeography
• Molecular Evidence
• Comparative anatomy
Best Conditions For Fossil
Formation
• Reduce the effects of scavenging animals
• Reduce the effects of decomposers by
having : Low oxygen levels
Low temperatures
Low moisture levels
• Reduce the action of wind and water
Example 1.
• Organism undergoes rapid burial by
sediment. This action reduces the
harmful effects of scavenging animals. It
also reduces the activity of bacteria and
protects the organism from erosion. Rapid
burial by sediment is likely to occur in
areas prone to flooding as well as many
marine environments.
Why would organisms sinking to the
bottom of a deep lake be a likely place
for fossils?
• Low oxygen levels
• Low temperature
• Disturbance from wind and water
minimised especially if coverage by
sediments occurs
What about caves and glaciers?
Fossilisation
During the process of fossilisation, in the
original organic matter that makes up the
organisms is chemically altered and turned
into stone. Fossilised wood, for example,
is much heavier than normal wood since it
is composed of stone. However, the
fossilised wood shows the structural
details of the original wood from which it
was derived.
Example
Fish dies and sinks to the sea floor
Water currents cover dead remains with sand before scavengers reach
it.
Depth of sea floor and burial sand reduce oxygen availability for decay,
bacteria
Weight of water and sediments apply pressure to dead remains,
replacing hard tissue such as bones with minerals.
How old is the that fossil?
We can determine this in a number of ways:
• Dating the absolute age of rock layers
above and below the fossil to give the
upper and lower range of its possible age
• Knowing the age of indicator fossils or
deposits found with the fossil that have
been date from similar sites elsewhere
• Dating the fossils absolute age
Relative age based on stratigraphy
• The principle of
superposition states that
older layers of rock are at the
bottom of a sequence and
the successively higher
layers are progressively
younger.
• Fossils aren’t found in
igneous rock, but because
we can date this rock with
radiometric methods, we can
determine the upper and
lower ages.
Index fossils
• Index fossils are
geologically short
lived species with a
limited occurrence
so that they are
restricted to a
particular strata.
The evidence of
such fossils in a
particular strata,
even in widely
separated regions,
are used to infer the
strata as being the
same age.
Absolute Age
• Radiometric dating is used to determine the age of a
rock.
• The method is based upon the radioactive decay of
unstable atoms to a more stable atom.
• In a certain period of time, called the half life, half of the
unstable atoms will have decayed into the more stable
atom.
• By measuring the ratio of unstable to stable decay
products, the time that has elapsed since the decay
began can be calculated. This is equivalent to the age of
the rock or fossil.
• Carbon-14 (Half-life: 5730 years) is used to date objects
younger than 50,00 years.
• Potassium – 40 (Half-life: 8,400 years) can be used to
date object that are millions of years old
Geological time
• This time scale was developed
in the nineteenth century when
geologists observed that
particular rocks where
characterised by distinctive
groups of fossils.
• Names were based on areas
where they were first recognised
or on the distinctive nature of
the rocks.
• For convenience the geological
time scale divided the Earths
history into hierarchical
intervals. The most widely used
time intervals are Periods.
• The time interval predating the
appearance of the first abundant
fossils is called the
Precambrian.
The Precambrian Era
•
•
•
•
The oldest rock
4600 to 570 million years old
Contains the fewest fossils
The earliest fossils include stromatolites,
which are found in the Pilbara of Western
Australia and are dated at 3.3 to 3.5 billion
years old and are evidence of the
evolution of early prokaryotic organsims.
Stromatolites
The Palaeozoic Era
• Known as ancient time
• 570 to 230 million years old
• Marked by the appearance of a diversity of
animals.
• Trilobites were the most common marine,
multicellular animals of the early Cambrian era.
• The era ended with the formation of on singles
super continent, called Pangaea. This caused
reduced rainfall, extremes of temperature and
the mass extinction of many species. Known as
the Permian period.
Trilobites
The Mesozoic Era
• Known as ‘middle life’
• 250 to 65 million years ago
• Includes Triassic, Jurassic and
Cretaceous periods
• Often described as the age of reptiles
• At the end of the period there was a mass
extinction. 70% of animal species were
lost, including almost all large reptiles.
Dinosaurs
The Cenozoic Era
• Known as the beginning of modern life
• 65 million years ago to present
• Many more flowering plant and mammal
fossils
• During the Cenozoic period, monkeys and
apes also evolved, including in the last 3
million years our genus Homo.
Biogeographical Evidence
• Biogeography is the study of the
distribution of organisms. Distribution
patterns give clues to the evolutionary
history of organisms and the Earth itself.
• Such studies reveal that many organisms,
which appear to have a common
evolutionary origin, are know found in
widely separated parts of the world.
Observations
• Galaxiid fishes (freshwater) are present in
Australia, New Zealand, New Caledonia, South
America and South Africa.
• Different but related species of boabab trees are
found in Africa, Madagascar and Western
Australia.
• Various species of waratah are native to
Australia, South America and New Guinea.
• Different species of flightless birds are native to
Australia, New Guinea, New Zealand, South
America and Africa.
Explanation
The theory of continental drift explains this phenomenon:
• The continents are parts of crustal plates that make up
the Earth’s rocky surface and these plates move in
relation to one another.
• More than 135 million years ago, the landmasses of
Australia, New Zealand, Antarctica, India, Africa,
Madagascar and South America formed a single super
continent called Gondwana.
• Movement of crustal plates, also called tectonic plates,
has resulted in the break-up of this supercontinent.
• Over the last 65 million years, Australia separated from
Antarctica
• The shapes of the continent also show contours that
reflect how they may have once fitted together.
Gondwana- southern super
continent
Conclusion
• Ancestral species of different organisms
that already existed became isolated on
their respective continents and continued
to evolve (change) to their present forms.