Notes from specification
1. HOW AND WHY HAS CLIMATE CHANGED IN THE GEOLOGICAL PAST?
1.a. The Earth’s climate is dynamic.
● METHODS USED TO RECONSTRUCT PAST CLIMATE, INCLUDING:
- Marine and lake sediments
- Varves - layers of lake sediments (light bands= summer with coarse material and
winter = dark, fine material) - lake sediments also contain pollen (indicates
vegetation type) and diatoms (algae) - cell walls made of silica
- Law of superposition and relative dating
- Foraminifera - different species identified by their calcite shells and each species is
sensitive to different climatic conditions eg. Bulloides - cold and salty water
- Can be relative and absolute dated (carbon content in shells)
- Large spatial scale and abundance
- Multi-proxy eg. foraminifera, colour, carbon content, oxygen etc
- Some can be over 500 million years old
- Ice cores
- Ice core data has shown that since early 19th century, there has been a 40% increase
in CO₂ levels
- Can date back 800,000 years - most recent = 1.2 million years as of early 2025
- High resolution, preservation of annual layers = relative dating
- Limited spatial scale - confined to polar regions
- Oxygen isotopes - more O18 in ice cores = warmer years - can be cross referenced to
marine sediments - as more O18 in ice cores would mean less O18 in marine
sediments = convergence of evidence
- Tree rings
- Dendrochronology: 1 ring = 1 annule - allows climatic conditions to be recorded
- Smaller longevity of an average 1000 year life span for trees = limited temporal scale
- Indicates temperatures and other climatic patterns such as rainfall and CO₂
conditions - difficult to detangle cause and effect/ which factor
- Absolute dating due to carbon and organic content of trees
- Tree ring width is difficult to accurately and reliably measure/ interpret - thick ring =
good year of growth = warmer temps
- Need to be in a good condition, older trees are prone to decay and disease = reduced
reliability
- Fossils
- Plants and animals require specific environmental conditions to survive - analyse
types of species and shell compositions - indicates climate they lived in
- Provides data over millions of years - oldest fossil = 3.5 billion years old
, - Multiple climate variables indicated such as temperature (oxygen isotopes in shells),
precipitation (leaf shapes and patterns)
- Fossils of foraminifera can also exist = ocean climatic conditions
- Potential contamination or evolutionary changes - taphonomic bias (issues such as
decay when fossilised) may skew data
- Novels : General overview of climate due to qualitative descriptions
- Eg. “A Christmas Carol” by Charles Dickens aligns with the ‘Little Ice Age’ - written in
1843
- Can be exaggerated = reduced reliability
- Novels only exist as long as humans have existed and been literate
Uniformitarianism: “the present is the key to the past” - past climates are able to be reconstructed
using present day methods (paleoclimatic indicators/ proxies)
Convergence of evidence: the most reliable conclusions are made from multi-proxy analysis
Law of superposition: within a core, the age of the sediment or ice is in relation to its depth eg.
deeper= older - uses RELATIVE DATING
● PAST CLIMATE TO REVEAL PERIODS OF GREENHOUSE AND ICEHOUSE EARTH,
INCLUDING:
- Long term, 100 million year transition to colder global climate conditions
- During the mid Cretaceous period 100 million years ago, temperatures were 6-8℃
warmer - subtropical conditions existed and there were no ice caps
- Atmospheric CO₂ levels were 5x higher
- Continents had a different configuration which affected ocean circulation and
currents
- Greenhouse conditions = high temps and atmospheric CO₂ levels
- Changes over a hundred million years to icehouse conditions = opposite
- Major tectonic changes moved continents and affected Earth’s energy balance,
resulting in cooling down
- Glaciation of Antarctica around 35 million years ago
- Today the entire continent of Antarctica is covered by a vast ice cap - 98% is covered
by ice - 30 million km3 of ice
- Yet 40 million years ago, fossils show that the continent experienced subtropical
conditions
- The descent of Antarctica into a permanent icehouse state occurred approximately
35 million years ago
- CO₂ level dropped abruptly from 1000 ppm to 600 ppm
1. HOW AND WHY HAS CLIMATE CHANGED IN THE GEOLOGICAL PAST?
1.a. The Earth’s climate is dynamic.
● METHODS USED TO RECONSTRUCT PAST CLIMATE, INCLUDING:
- Marine and lake sediments
- Varves - layers of lake sediments (light bands= summer with coarse material and
winter = dark, fine material) - lake sediments also contain pollen (indicates
vegetation type) and diatoms (algae) - cell walls made of silica
- Law of superposition and relative dating
- Foraminifera - different species identified by their calcite shells and each species is
sensitive to different climatic conditions eg. Bulloides - cold and salty water
- Can be relative and absolute dated (carbon content in shells)
- Large spatial scale and abundance
- Multi-proxy eg. foraminifera, colour, carbon content, oxygen etc
- Some can be over 500 million years old
- Ice cores
- Ice core data has shown that since early 19th century, there has been a 40% increase
in CO₂ levels
- Can date back 800,000 years - most recent = 1.2 million years as of early 2025
- High resolution, preservation of annual layers = relative dating
- Limited spatial scale - confined to polar regions
- Oxygen isotopes - more O18 in ice cores = warmer years - can be cross referenced to
marine sediments - as more O18 in ice cores would mean less O18 in marine
sediments = convergence of evidence
- Tree rings
- Dendrochronology: 1 ring = 1 annule - allows climatic conditions to be recorded
- Smaller longevity of an average 1000 year life span for trees = limited temporal scale
- Indicates temperatures and other climatic patterns such as rainfall and CO₂
conditions - difficult to detangle cause and effect/ which factor
- Absolute dating due to carbon and organic content of trees
- Tree ring width is difficult to accurately and reliably measure/ interpret - thick ring =
good year of growth = warmer temps
- Need to be in a good condition, older trees are prone to decay and disease = reduced
reliability
- Fossils
- Plants and animals require specific environmental conditions to survive - analyse
types of species and shell compositions - indicates climate they lived in
- Provides data over millions of years - oldest fossil = 3.5 billion years old
, - Multiple climate variables indicated such as temperature (oxygen isotopes in shells),
precipitation (leaf shapes and patterns)
- Fossils of foraminifera can also exist = ocean climatic conditions
- Potential contamination or evolutionary changes - taphonomic bias (issues such as
decay when fossilised) may skew data
- Novels : General overview of climate due to qualitative descriptions
- Eg. “A Christmas Carol” by Charles Dickens aligns with the ‘Little Ice Age’ - written in
1843
- Can be exaggerated = reduced reliability
- Novels only exist as long as humans have existed and been literate
Uniformitarianism: “the present is the key to the past” - past climates are able to be reconstructed
using present day methods (paleoclimatic indicators/ proxies)
Convergence of evidence: the most reliable conclusions are made from multi-proxy analysis
Law of superposition: within a core, the age of the sediment or ice is in relation to its depth eg.
deeper= older - uses RELATIVE DATING
● PAST CLIMATE TO REVEAL PERIODS OF GREENHOUSE AND ICEHOUSE EARTH,
INCLUDING:
- Long term, 100 million year transition to colder global climate conditions
- During the mid Cretaceous period 100 million years ago, temperatures were 6-8℃
warmer - subtropical conditions existed and there were no ice caps
- Atmospheric CO₂ levels were 5x higher
- Continents had a different configuration which affected ocean circulation and
currents
- Greenhouse conditions = high temps and atmospheric CO₂ levels
- Changes over a hundred million years to icehouse conditions = opposite
- Major tectonic changes moved continents and affected Earth’s energy balance,
resulting in cooling down
- Glaciation of Antarctica around 35 million years ago
- Today the entire continent of Antarctica is covered by a vast ice cap - 98% is covered
by ice - 30 million km3 of ice
- Yet 40 million years ago, fossils show that the continent experienced subtropical
conditions
- The descent of Antarctica into a permanent icehouse state occurred approximately
35 million years ago
- CO₂ level dropped abruptly from 1000 ppm to 600 ppm
