This page is optimized for mobile devices, if you would prefer the desktop version just
click here
Summary
-
Life’s History:
- The extremely long time periods in the earth’s history are divided into eons, eras and periods for easier study.
- 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.
-
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.
-
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.
-
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.
-
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.
Read also:
OpenStax, Siyavula: life sciences grade 10. OpenStax CNX. Apr 11, 2012 Download for free at http://cnx.org/content/col11410/1.3
Google Play and the Google Play logo are trademarks of Google Inc.