Review

Summary of Environments Through Time This summary has been taken directly from the HSC Spotlight Earth and Environmental Science Text pages 60-61ReviewEvidence from early Earth indicates the first life forms survived in changing habitats during the Archaean and Proterozoic eons.Lesson 1SummaryGeologic time is divided into eons: HadeanArchaeanProterozoicPhanerozoic

It is divided using fossil evidence of various life formsSummaryCyanobacteria are simple photosynthetic organisms. Western Australia has some of the worlds most significant fossil evidence of cyanobacteria.

Both fossil and modern stromatolites are similar in structure. The distribution of stromatolites has changed over time

Banded iron formations give us evidence of environmental conditions when they were formed.

Dot PointsDiscuss DOT Points 1.3-1.6SummaryFossilisation is a rare process because certain conditions must be present. There are three major types of fossilisation:MouldsCasts Carbonisation

Isotopes can give evidence for the presence of life

DOT PointDiscuss DOT Points 1.7-1.8Environments of the Phanerozoic & The Cambrian eventLesson 2SummaryThe formation of the ozone layer could only take place once the concentration of oxygen had built up in the atmosphere

A chemical reaction (photolysis) takes place in the stratosphere to change oxygen into ozone

Ozone filters out ultraviolet radiation. This made the terrestrial environment much less harmful and enabled evolution onto landDOT PointDiscuss DOT Points 2.1-2.4SummaryThe age of a fossil can be determined by interpreting its position in a stratigraphical sequence

Relative dating is carried out by interpreting the position of a rock/fossil in a stratigraphic section to determine its age in relation to other rocks/fossils. It gives the age as a geological period.

Absolute age is determined by radiometric dating with isotopes. It gives a numerical value of ageSummaryThe numerous fossils of hard-bodied organisms in the Cambrian show both the explosion of new life forms and higher rates of preservation

Hard-bodied organisms have many advantages over soft-bodied organisms

Evolution occurs via the mechanisms of mutation and natural selectionDOT PointDiscuss DOT Points 3.1, 3.4, 3.5Exploiting new environmentsLesson 3SummaryMany lines of evidence show how organisms in the past have evolved into modern-day organisms

Organisms faced with environmental pressures when they made the transition from the marine to the terrestrial environment

Significant organisms that were initiators in the transition were liverworts, arthropods/insects, crossopterygians/lungfish and amphibiansDOT PointsDiscuss DOT Points 4.1, 4.3, 4.6, 4.7Past extinction and mass extinction eventsLesson 4SummaryThe first land dwellers were able to gain certain advantages over their marine relatives

There are times throughout geological history when evolution moves at either a gradual of an explosive rate. The latter often follows a mass extinction

A mass extinction is different from a small extinction as it affects entire groups of organisms on a global scaleDOT PointsDiscuss DOT Points 5.2, 5.4, 5.5SummaryAustralia has undergone in the past a small extinction of megafauna. The cause is likely to be because of wither climate change as the continent moved or human impact.

The mass extinction at the end of the Permian is thought to have resulted from global climate change caused by large scale glaciation

The mass extinction at the end of the Cretaceous is thought to have resulted from global climate change by a meteorite impactSummaryAustralia is not experiencing an increased rate of extinction compared with and in the last 60 million years owing to human influences DOT PointsDiscuss DOT Points 5.6-5.8