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.

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• Russell, P.J., Hertz, P.E., McMillan, B. 2012. Biology: The dynamic Science. Brooks-Cole Cengage Learning. 14: 286-302.

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• Starr, C., Taggart, R., Evers, C. and Starr, L. 2013. Biology: The unity and diversity of life. Brooks-Cole Cengage Learning. 8:124-132.

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