origin of nature

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
 IT ISN’T EASY to become a fossil. The fate of nearly all
living organisms—over 99.9 percent of them—is to
compost down to nothingness. When your spark is gone,
every molecule you own will be nibbled off you or sluiced
away to be put to use in some other system. That’s just
the way it is. Even if you make it into the small pool of
organisms, the less than 0.1 percent, that don’t get
devoured, the chances of being fossilized are very small.

4. THE FORMATION OF MINERALISED
FOSSILS
 In order to become a fossil, several things must happen. First,
you must die in the right place. Only about 15 percent of rocks
can preserve fossils, so it’s no good keeling over on a future
site of granite. In practical terms the deceased must become
buried in sediment, where it can leave an impression, like a
leaf in wet mud, or decompose without exposure to oxygen,
permitting the molecules in its bones and hard parts (and very
occasionally softer parts) to be replaced by dissolved
minerals, creating a petrified copy of the original. Then as the
sediments in which the fossil lies are carelessly pressed and
folded and pushed about by Earth’s processes, the fossil must
somehow maintain an identifiable shape. Finally, but above all,
after tens of millions or perhaps hundreds of millions of years
hidden away, it must be found and recognized as something
worth keeping. Only about one bone in a billion, it is thought, ever
becomes fossilized

5. THE FORMATION OF MINERALISED
FOSSILS
 Fossils are in every sense vanishingly rare. Most of
what has lived on Earth has left behind no record at
all. It has been estimated that less than one species
in ten thousand has made it into the fossil record.
That in itself is a stunningly infinitesimal proportion.
However, if you accept the common estimate that
the Earth has produced 30 billion species of creature
in its time and Richard Leakey and Roger Lewin’s
statement (in The Sixth Extinction ) that there are
250,000 species of creature in the fossil record, that
reduces the proportion to just one in 120,000. Either
way, what we possess is the merest sampling of all
the life that Earth has spawned.

6. THE FORMATION OF MINERALISED
FOSSILS
 Moreover, the record we do have is hopelessly
skewed. Most land animals, of course, don’t die
in sediments. They drop in the open and are
eaten or left to rot or weather down to nothing.
The fossil record consequently is almost
absurdly biased in favor of marine creatures.
 About 95 percent of all the fossils we possess
are of animals that once lived under water,
mostly in shallow seas.

7. 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.

8. THE FORMATION OF MINERALISED FOSSILS
continuous
 As covered bones decay  minerals seep in
replacing 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 fill with minerals
making a stone replica of the organism.

9. THE FORMATION OF MINERALISED
FOSSILS CONTINUOUS

10. RELATIVE DATING:
Determining relative order of past
events, without determining their
absolute age.
Determines which fossils are older or
younger.
Easy to determine 
 which geological deposit they come from
 the Law of Superposition.

11. THE LAW OF SUPERPOSITION:
o 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.

13. Undisturbed Sedimentary Rock & its
Fossils in Upper strata generally contain
fossils of younger, more complex
organisms,
Lower strata contain fossils of simpler
life forms
 There is a tendency toward increasing
complexity in life forms over time

14. ABSOLUTE RADIOACTIVE DATING:
Process of determining an FAIRLY
ACCURATE age for site or artefact.
based on physical/chemical properties
of materials of artefacts.
Provides a numerical age for the material
tested,
relative dating can only provide a
sequence of age.

15. Radiometric dating  based on
constant rate of decay of
radioactive isotopes.
1 of most widely used and well-
known absolute radiometric dating
techniques is
 carbon-14 (or radiocarbon) dating
 used to date organic remains.

16.  Carbon-14 moves becomes part of food chain 
animals eat plants and predators eat other
animals.
 With death  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 ¼ of original
carbon-14 will remain.
 After yet another 5,730 years only one-eighth
will be left.

17. Scientists determine date of death of organic
matter in artefact  measuring proportion of
carbon-14 in organic material.
Other radiometric dating techniques
include:
potassium-argon dating (K-Ar dating).
Potasium-40 is radioactive isotope of
potassium that decays into argon-40.
Half-life of potassium-40 is 1.3 billion
years  longer than that of carbon-14,
allowing much older samples to be
dated.

18. 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.

19.  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.

20.  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.

21.  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

22. Thrinaxodon

23. 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.

24. 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.

25. 3. Permian–Triassic extinction event
– 251 Mya. Earth's largest extinction
killed 57% of all families and 83% of all
genera including insects.

26. 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.

27. The recovery of vertebrates took 30
million years, but the vacant niches
created the opportunity for archosaurs
to become ascendant.
In the 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".

28. 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.

29. 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.

30. 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.

32. 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.

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

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

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

36.  Primitive Cone-bearing plants

37.  First mammals found in Eastern Cape and Lesotho

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

39. Part of 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

40.  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.