Topic 13: History of life on Earth

1. Core content

Life’s History:Change throughout the history of life on Earth

• Changes in the composition of the atmosphere (eg. increases in the levels of oxygen)

• changes in climate (eg. ice ages)

• geological events (eg. movements of continents) and their effect on the distribution of living organisms (biogeography)

Evidence for changing sea level and rise and fall of the land (eg. bivalves and ammonites found on the Makhatini Flats in Northern KZN, whale fossils in the Sahara, trilobites in the Karoo

• The three eras: Paleozoic, Mesozoic and Coenozoic periods are each divided into periods (Names of periods not to be memorised):

• Geological Timescale

The meaning and use of timescales (details not to be memorised).

• Cambrian Explosion

The Cambrian Explosion, which gives us insights into the origins of the major forms of all animal groups. In the last four million years, significant changes have occurred in species occurring in Africa (e.g., humans) (Link with Grade 12).

• Mass Extinctions

There have been five mass extinctions throughout history, two of which are particularly important: 250 mya (the extinction of about 90% of all life on Earth) and 65 Mya (the extinction of many species, including the dinosaurs).

The rate of extinction on the Earth at present is higher than at any time in the past. The present time has been called the sixth extinction (Links to Grades 11 and 12).

• Fossil Formation and Methods of Dating Them

Fossil formation and methods of dating them, e.g., radiometric dating and relative dating.

• Key Events

There is evidence from South Africa of certain key events in life’s history:

• origins of the earliest forms of life: evidence of single celled fossilised bacteria (stromatolites) from many parts of South Africa;

• soft-bodied animals in Namibia, Northern Cape;

• early land plants in the Grahamstown area;

• forests of primitive plants such as Glossopteris near Mooi River and Estcourt;

• location of coal deposits in South Africa (map only);

• the coelacanth as a ‘living fossil’ found on the Northern KwaZulu-Natal coast;

• mammal-like reptiles found in the Karoo (e.g. Lystrosaurus and Thrinaxodon);

• dinosaurs (in the foothills of Drakensberg and Maluti mountains), as well as cone-bearing plants;

• early mammals (Eastern Cape and Lesotho);

• humans and pre-humans (eg Gauteng, (Cradle of Humankind) Namibia, North West (Taung), Free State (Florisbad), KwaZulu-Natal (Border Cave) and, Limpopo (Makapansgat)).

Understanding Fossils

• Scientists use deductive reasoning (inference) to understand fossils and the history of life on Earth. The impact of humans on biodiversity and the natural environment.

Fossil Tourism

Fossil tourism is a source of income and employment in some localities.