Topic 6

Climactic VariationTopic 6IntroductionIn this part you will study climactic variations over time and the evidence used to determine these changes.

There is abundant evidence from a variety of sources to suggest the Earths climate has changed. In this section we will look at this evidence.Evidence for past climatesLesson 1Temperature RecordSince the mid-1800s accurate temperature records have been kept. This allows scientists to make direct comparisons with current statistics.

DendrochronologyThis is the study of tree rings. Ancient trees can provide a record of their growth and development dating back to 8000 years.

Glacial DepositsGlaciers are huge rivers of ice that scrape and gouge soil, dirt and rock beneath them. This material is deposited as sediments at the end of the glacier. Scientists can map these deposits and give them an indication of past climate in that area.

Sea LevelsWhen the Earths temperature changes, the amount of sea water that turns into ice at the poles fluctuates. This fluctuation causes sea levels to rise and fall. Scientists have mapped and dated shoreline features which show us the sea level in the past.

Geological FormationsWe find remains of marine organisms in outback Australia. This is an indication that climates have changed significantly. Fossil records can also show us that most of Australia was once covered by rainforests.

Marine SedimentsThe sediments on the ocean floor reveal organisms that absorb oxygen from sea water. Scientists analyse the oxygen in these sediments which can give us an idea of past ocean temperatures and therefore climate information.

Marine SedimentsOxygen has two stable isotopes: oxygen-16 and oxygen-18. When marine organisms take up oxygen they acquire these isotopes in a ratio reflecting what it was in the water. When it dies, its hard parts sink to the ocean floor and preserve the ratio of oxygen isotopes.

Ice CoresStudying ice cores is unlike all the other forms of evidence. Ice cores give scientists direct analysis of gases from ancient atmospheres. As snow falls it absorbs the gases in the air. As it accumulates it turns into ice and locks the traces of the atmosphere within it. By drilling into ice in Antarctica and studying the cores, scientists are able to measure and determine changes in atmospheric gases.

HomeworkRead pages 35-36 Prelim Spotlight Text

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Complete DOT Point 5.2, 5.3, 5.4