1. UNIT 6:
HISTORY OF LIFE
ON EARTH

2. PALAEONTOLOGY:
The study of fossil records to
discover the history of life, ancient
climates and environments.
UNIT 10: BIOSPHERE, BIOMES AND
ECOSYSTEMS

3. THE FORMATION OF MINERALISED
FOSSILS
Fossils are formed in a number of different
ways:
 Most are formed when a plant or animal
dies in a watery environment.
 And is buried in mud and silt.
 Soft tissues quickly decompose leaving the
hard bones or shells behind.
 Over time sediment builds over the top
 And hardens into rock.

4. THE FORMATION OF MINERALISED FOSSILS
continuous
 As the encased bones decay, minerals seep in
replacing the organic material cell by cell in a
process called "petrification."
 Alternatively the bones may completely decay
leaving a cast of the organism.
 The void left behind may then fill with minerals
making a stone replica of the organism.

5. THE FORMATION OF MINERALISED
FOSSILS CONTINUOUS

6. FOSSIL DATING:
 Method used to determine the age of fossils or the
strata (layer of sediment) in which they are found.
 Example of methods;
o Relative dating methods
o Absolute dating methods like Radioactive dating.


7. RELATIVE DATING:
 The science determining the relative order
of past events, without necessarily
determining their absolute age.
 Determines which fossils are older or
younger.
 Easy to determine based on which
geological deposit they come from and the
Law of Superposition.

8. The Law of Superposition:
o States that the older layer lies underneath
the younger layer in undisturbed contexts.
o Deeper layers are older than fossils from
layers closer to the surface of the earth.
o The higher up you go in an undisturbed rock
stratum (rock layer), the younger the rock layers
become and therefore it is believed the fossils
within these layers, are also younger than the
fossils beneath them

9.  Undisturbed Sedimentary Rock and its Fossils
in Upper strata generally contain fossils of
younger, more complex organisms,
whereas, the lower strata contain fossils of
simpler life forms
 There is a tendency toward increasing
complexity in life forms over time

10. ABSOLUTE RADIOACTIVE DATING:
 The process of determining an approximate age for
an archaeological or paleontological site or artefact.
 usually based on the physical or chemical
properties of the materials of artefacts.
 provides a numerical age for the material tested,
while relative dating can only provide a sequence of
age.
 Radiometric dating is based on the constant rate of
decay of radioactive isotopes.
 One of the most widely used and well-known
absolute radiometric dating techniques is carbon-
14 (or radiocarbon) dating, which is used to date
organic remains.

11.  Carbon-14 moves up the food chain as
animals eat plants and as predators eat
other animals.
 With death, the uptake of carbon-14 stops.
 unstable isotope starts to decay into
nitrogen-14. It takes 5,730 years for half the
carbon-14 to change to nitrogen; this is the
half-life of carbon-14. After another 5,730
years only one-quarter of the original
carbon-14 will remain.
 After yet another 5,730 years only one-
eighth will be left.

12.  Scientists can determine the date of death of an
organic matter in an artefact, by measuring the
proportion of carbon-14 in the organic material.
 Other radiometric dating techniques include;
 potassium-argon dating (K-Ar dating).
 Potasium-40 is a radioactive isotope of
potassium that decays into argon-40. The
half-life of potassium-40 is 1.3 billion
years, far longer than that of carbon-14,
allowing much older samples to be dated.

13.  Scientists
use the results from fossil dating
to make inferences about the age of a fossil,
which can be used to determine which
organisms lived when, and when did some
organisms became extinct.

14. GEOLOGICAL TIMESCALES:
 Provides a system of chronologic
measurement relating to time that is used by
earth scientists e.g geologists and
palaeontologists to describe the timing and
relationships between events that have
occurred during the history of the Earth.
 Evidence from radiometric dating indicates
that the Earth is about 4.570 billion years
old.

15.  Geological time scale is divided into different
Eon’s which is divided into different Era’s, divided
into different Periods, divided into different
Epochs. (See geological timescale below)
 What caused the change in the different era’s,
and periods on the geological timescale? Climate
changes e.g. increase in oxygen levels, ice ages
and geological events e.g. movement of
continents.
 Know the three era’s: Paleozoic, Mesozoic and
Coenozoic era.

17.  Each era on the scale is separated from the next
by a major geological or paleaontological event or
change like mass extinctions.
 E.g boundary between the Cretaceous period and
the Paleocene period is defined by the
Cretaceous–Tertiary extinction event, which
denotes the end of the dinosaurs and of many
marine species.

18.  In the geological timescale know the major events and life
forms in each era.
 The Cambrian explosion is important because it is the
origin of early forms of all animal groups. Life-forms
have gradually changed to become present life-forms.
 The Missing link between dinosaurs and birds are the
Archaeopteryx, the missing link between the fish and the
amphibians are the coelacanth and the missing link
between the reptiles and mammals are the Thrinaxodon.
• Archaeopteryx

19. Thrinaxodon

20. MASS EXTINCTIONS:
There has been five mass extinctions:
1. Cretaceous–Tertiary extinction event –
65.5 Mya. About 17% of all families, 50%
of all genera and 75% of species became
extinct.
 In the seas it reduced the percentage of
sessile animals to about 33%. Mammals
and birds emerged as dominant land
vertebrates in the age of new life.

21. 2. Triassic–Jurassic extinction
event– 205 Mya. About 23% of all
families and 48% of all genera
(20% of marine families and 55%
of marine genera) went extinct.
 Most non-dinosaurian
archosaurs, most therapsids,
and most of the large
amphibians were eliminated,
leaving dinosaurs with little
terrestrial competition.

22.  Non-dinosaurian archosaurs
continued to dominate aquatic
environments, while non-
archosaurian diapsids
continued to dominate marine
environments.
 The Temnospondyl lineage of
large amphibians also survived.

23. 3. Permian–Triassic extinction event
– 251 Mya. Earth's largest extinction
killed 57% of all families and 83% of all
genera (53% of marine families, 84%
of marine genera, about 96% of all
marine species and an estimated 70%
of land species) including insects.

24.  The evidence of plants is less clear,
but new taxa became dominant after
the extinction. The "Great Dying" had
enormous evolutionary significance:
on land, it ended the primacy of
mammal-like reptiles.

25.  The recovery of vertebrates took 30
million years, but the vacant niches
created the opportunity for archosaurs
to become ascendant.
 Inthe seas, the percentage of animals
that were sessile dropped from 67% to
50%. The whole late Permian was a
difficult time for at least marine life,
even before the "Great Dying".

26. 4. Late Devonian extinction – 360–
375 Mya. A prolonged series of
extinctions eliminated about 19% of
all families, 50% of all genera and
70% of all species.
 This extinction event lasted perhaps
as long as 20 MY, and there is
evidence for a series of extinction
pulses within this period.

27. 5 Ordovician–Silurian extinction
event– 440–450 Mya. Two events
occurred that killed off 27% of all
families and 57% of all genera.
 Together they are ranked by many
scientists as the second largest of the
five major extinctions in Earth's
history in terms of percentage of
genera that went extinct.

28. KEY EVENTS IN LIFE’S HISTORY IN SOUTHERN
AFRICA
 Origins
of the earliest forms of life:
evidence of fossilized bacteria
(stromatolites) from caves found in the
Barberton district, Mpumalanga and
many other caves.

30.  Soft bodied animals in Namibia
 Early land plants in the Grahamstown
area.
 Forests of primitive plants such a
Glossopteris which form most of the
coal deposits in southern Africa.

31.  The Coelacanth as a living fossil of the group that is
ancestral to amphibians.

32.  Mammal like reptiles in the Karoo e.g.
Thrinaxodon and Lystrosaurus
 Thrinaxodon
• Lystrosaurus

33.  Dinosaurs found in the Drakensberg and Maluti
mountains e.g. Euskylosaurus from Lady Brand in
the Free State and cone bearing plants.

Euskylosaurus

34.  Primitive Cone-bearing plants

35.  First mammals found in Eastern Cape and Lesotho

36.  Humans fossil found in Gauteng, Free State,
Kwazulu Natal, Western Cape and Limpopo

37.  Partof the skeleton of
Australopithecus sediba from the
Malapa site in South Africa. Two partial
skeletons unearthed in a cave belong
to a previously unclassified species –
which could be an early human
ancestor – dating back almost 2 million
years

38.  Sterkfontein's first piece de resistance: the
Australopithecus africanus Mrs Ples (now believed
to be a Mister Ples), dating back 2.5-million years,
found by Robert Broom in 1947. The fossil provided
proof that Australopithecus could be classified as a
member of the Hominidae (the family of humans)
and established Africa as the Cradle of Humankind.