HISTORY OF LIFE ON EARTH
PALAEONTOLOGY:
•The study of fossil records to discover the history of life, ancient climates and environments
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.
THEFORMATION 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.
THE WAY MINERALISED FOSSILS ARE FORMED
DATING OF MINERAL FOSSILS
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
oAbsolute dating methods like Radioactive dating.
The Law of Superposition
oStates that the older layer lies underneath the younger layer in undisturbed contexts.
oDeeper layers are older than fossils from layers closer to the surface of the earth
CONTINUATION OF FOSSIL DATING
• 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.
KEY EVENTS IN LIFE’S HISTORY IN SOUTHERN AFRICA
• There were a few key events in life’s history which there is evidence from 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.
THE EVENTS
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.
Mammal like reptiles in the Karoo e.g. Thrinaxodon
Thrinaxodon
Dinosaurs found in the Drakensberg and Maluti mountains e.g. Euskylosaurus from Lady Brand in the
Free State and cone bearing plants
Euskylosaurus
Primitive Cone-bearing plants
First mammals found in Eastern Cape and Lesotho
Humans fossil found in Gauteng, Free State, Kwazulu Natal, Western Cape and Limpopo
CONTINUATION OF THE EVENTS
• 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
THE EVIDENCE OF AUSTRALOPITHECUS
• 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 Bloom 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.
REFERENCES
• Campbell, N.A., Reece, J.B., Urry, L.A., Cain, M.L., Wasserman, S.A., Minorsky, P.V., Jackson, R.B. 2010. Biology Eighth Edition. Pearson International. 16:305-336.
•
• Russell, P.J., Hertz, P.E., McMillan, B. 2012. Biology: The dynamic Science. Brooks-Cole Cengage Learning. 14: 286-302.
•
• Starr, C., Taggart, R., Evers, C. and Starr, L. 2013. Biology: The unity and diversity of life. Brooks-Cole Cengage Learning. 8:124-132.
•
•