Topic 3: The Evolution of Life on Earth

Life on Earth
Topic 6: Evidence Suggesting When Life Originated
Part of the Evolution of Australian Biota Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
DOT Point
 Describe some of the palaeontological and geological
evidence that suggests when life originated on Earth
 Explain why the change from an anoxic to an oxic
atmosphere was significant in the evolution of living things
Palaeontology is the
scientific study of fossils and all
aspects of extinct life.
Geology is the scientific study
of the origin, history and
structure of the Earth as
recorded in rocks.
These two studies are valuable
in combination to produce
evidence from the past.
Palaeontological Evidence
The discovery of two 3400-3500
million year-old Precambrian fossils
from Western Australia provided
some of the first evidence towards
the origin of life on Earth.
 Fossils of single celled anaerobic
procaryotes (microfossils) found
were very similar to those found
living today
 Fossilised remains of stromatolites
provided valuable information
about the structure of early
Palaeontological Evidence
Simple bacteria existed in
structures called
stromatolites which were
very similar to present day
living stromatolites. These
organisms live in shallow
marine environments.
Colonies of simple bacteria,
or cyanobacteria, trap layers
of calcium carbonate and
‘grow’ upwards in columns
towards the sun.
Palaeontological Evidence
Deposits of living stromatolites can be found in Western
Australia at Shark Bay, growing at a rate of about 1mm per year
with individual domes reaching a diameter of about 200cm and
a height of about 50cm.
Palaeontological Evidence
The 1999 discovery of what could be the remains of
nanobacteria or nanobes, in a meteorite from Mars (found
in Antarctica) indicated similarities to nanobes discovered in
Queensland in 1996.
Palaeontological Evidence
Nanobes are filiment-type structures found in rock. The
nanobes found on Mars were able to withstand radiation, cold
and acidic conditions, a time when the environment on Mars
may have paralleled that existing on Earth for a few hundred
Palaeontological Evidence
Given the presumed sharing of debris generated from
meteorite impacts amongst the early planets, the origins of the
nanobes on Mars and Earth may be the same.
Palaeontological Evidence
Some scientists hypothesise that nanobes are the smallest form
of life (they are 10 times smaller than our smallest bacteria).
However, some researchers believe nanobes to be merely
crystal growths. The debate continues!
Palaeontological Evidence
In general, palaeontologists using the fossil evidence from
different rock layers have found that the more primitive cells
and marine organisms are found in the lower layers of rock
compared to the more complex and land-dwelling
Palaeontological Evidence
This trend suggests that simple organisms evolved into more
complex organisms and marine organisms preceded landdwelling organisms.
We can make inferences about extinct organisms by studying
their closest modern living relatives.
Palaeontological Evidence
2500 million year-old Archaean rocks from north Western
Australia were examined by scientists in 1999. They found
biomarkers or chemical evidence, for the existence of
Biomarkers are chemicals that are produced by only one group
of organisms providing evidence of their existence in the past.
Palaeontological Evidence
Oxidised rocks such as banded iron and red bedrock formations
provide geologic evidence towards the origin of photosynthetic
Change of Atmospheric Gases
Photosynthetic life changed the world forever. For the first
time, Carbon Dioxide was being removed from the atmosphere
and free oxygen was being added.
Change of Atmospheric Gases
An anoxic atmosphere is one defined as being deficient, or
lacking, in oxygen. An oxic atmosphere is one where oxygen
is available. A change from an anoxic to an oxic atmosphere
with plenty of free oxygen had a significant influence on the
conditions of early Earth and the evolution of living things.
Change of Atmospheric Gases
Anerobic organisms began to decline while photosynthetic
organisms became more abundant. Today anerobic organisms
only survive in environments with very low oxygen
concentration, such as swamps, bogs, deep underground or in
deep ocean hydrothermal vents.
Change of Atmospheric Gases
Aerobic organisms became more efficient in energy production
(respiration) which led to an increase in activity and eventually
led to an increase in complexity and size of these organisms
Change of Atmospheric Gases
As the oxygen in the atmosphere accumulated, it started
reacting with the sun’s ultraviolet radiation. The ozone layer
(O₃) began to form and block out harmful radiation from the
Change of Atmospheric Gases
This reduced the amount of ultraviolet radiation reaching the
Earth’s surface and had significant influence on future
organisms as it protected them from dangerous radiation and
enabled them to move onto land!
-Students to complete DOT Point 2.3

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