10.6 4.2.7 summary

Summary

1. Life’s History:

   1. The extremely long time periods in the earth’s history are divided into eons, eras and periods for easier study.
   2. Continental drift occurred by means of plate tectonic movements. The supercontinent Pangaea split into Laurasia in the north and Gondwana in thesouth, ultimately forming today’s continents.

2. The Geological Time Scale:

• Before the Paleozoic era, life consisted of bacterial mounds called stromatolites, which oxygenated the atmosphere. The Cambrian explosion was asudden increase in complex multicellular life early n the Paleozoic era. Organisms underwent further changes later.
• The Paleozoic era ended with a massive extinction, killing many species. The Mesozoic era started, when the dominant life forms were conifers and dinosaurs.
• 65 mya, the Mesozoic ended and the Caenozoic started, with mammals and flowering plants becoming dominant. Human evolution also occurred in the latter stages of this era.

1. Missing Links:

• Archaeopteryx is the link between dinosaurs and birds – it has teeth, feathers, a bony long tail and claws on its forelimbs.
• The coelacanth is the link between amphibians and fish. It has lobed fins, primitive internal organs and nostrils that go right through into the mouth.

1. Fossils:

• Fossils are formed in sedimentary rocks only over long periods.
• They can be casts, moulds, mineralized body parts like bones / shells, imprints, film fossils or even dung samples.
• Fossils are dated using carbon 14 dating (fairly recent organic samples only) or radiometric dating for older fossils.
• Fossil sites bring in many tourists and can be important for the economy.
• Some ancient organisms are seen as “living fossils” – they were believed extinct, but are still present, e.g. the coelacanth and tuatara.

1. Key events in the history of life:

• Stromatolite fossils were found in Barberton and fossils of soft-bodied animals in Namibia.
• Ancient plant fossils like Glossopteris are present in central KZN and near Grahamstown.
• The coelacanth was ‘rediscovered’ by the East London museum in 1938.
• Mammal-like reptile fossils were found in the Karoo – they have advanced palates and complex ear bones, unlike true reptiles. They are calledtherapsids.
• Dinosaur fossils can be seen in the Drakensberg and Maluti mountains. This are also has fossils of the earliest small mammals.
• Pre-human fossils like Australopithecus have been found in the Sterkfontein area and nearby places. This is unique – nowhere else in the world do these fossils occur. The majority of thesefinds were made by paleontologists from Wits University.