Evidence for Climate Variation

Question 1

Pollen grains in sedimentary rocks

Answer 1

• Pollen is the male gametes of flowering plants; they are small and produced in large quantities, which allows for wide distribution and ensures their preservation.
• Because pollen grains are well preserved in lakes, grain analysis shows the plant types present when the sediment was deposited; inferences can be made about climate eg, alpine pollen = cold climate
• Pollen is produced in large quantities, resistant to decay due to their sporopollenin walls, and widely distributed; however, analysing it is costly and timely.

Question 2

changes in rock types

Answer 2

• Characteristics of different rocks depend on the environment the sediments were deposited in
• Sand and gravel are dropped by melting glaciers and form till, which indicates a cold glacial climate
• Seawater easily evaporates in high temperatures and leaves behind a layer of salt, which is preserved in the rock and indicates a warm climate
• Various rocks can be dated to give a timeframe of climate variation.

Question 3

fossils and microfossils

Answer 3

• Fossils show environmental changes, as organisms require specific conditions to survive
• Calcareous fossils are made of calcium carbonate and provide oxygen isotopes to infer past temperatures, while siliceous fossils are made of silica and provide oxygen isotopes to show conditions of ocean surfaces
• Microfossils are 4 millimetres in size, and are minuscule life forms, the calcium carbonate infer past temperatures and indicates a reduction in rainfall as Australia was once covered by forested plains
• Fossils are unique to specific climatic conditions, making evidence reliable and accurate; however, only marine organisms are readily preserved

Question 4

changing isotope ratios in rocks and deep sea sediments

Answer 4

• Oxygen-18 is heavier than oxygen-16, as it has more neutrons; when water evaporates from ocean surfaces, more isotopically light oxygen-16 evaporates.
• During non-glacial periods with warm climate, water is deposited onto land as rain and runs off into the ocean; this water contains isotopically light oxygen-16.
• During glacial periods with cold climate, moisture is stored in clouds and falls as snow on a continent, accumulating into a continental ice sheet; more isotopically light oxygen-16 is stored in the continent, while seawater is enriched with the heavier oxygen-18

Question 5

identify more recent evidence of climate variation, including but not limited to:
- Aboriginal art sites showing now-extinct species and environments

Answer 5

• Rock paintings in Arnhem Land, Northern Territory show now-extinct species, like the numbat and thylacine.
• This indicates that the species lived alongside Indigenous communities, but eventually became extinct due to environmental changes, such as rising sea levels and desertification, caused by climate variation

Question 6

changing isotope ratios in rocks and deep sea sediments how is it measured

Answer 6

• When marine organisms take in oxygen, when it dies, its shell of calcium carbonate preserves these ratios as it sinks to the seafloor and becomes entrapped in sediment
• Due to the known ratio, seafloor sediments are measured for oxygen isotopes to determine glacial periods; however, plate tectonics can destroy the seafloor