Our Changing Planet

Why is understanding the changing planet important?

Helps understand present-day environment, Earth system processes, predict future changes, and provides context for evolution including humans

What are the Earth’s main spheres?

Atmosphere, hydrosphere, biosphere, lithosphere, cryosphere

What is the relationship between drivers and climate change?

External forcing → climate system interactions → climate variations

Why can small changes in drivers have big effects?

Feedbacks within the Earth system amplify small changes

How old is the Earth?

~4.5 billion years old

How old is the Moon?

~4.5 billion years, formed shortly after the solar system/earth

Meaning of ‘ka’

Thousands of years ago

Meaning of ‘Ma’

Millions of years ago

Meaning of ‘kyr’

Duration of thousand years

What are instrumental records?

Direct measurements of environmental variables

Examples of instrumental records

Temperature, atmospheric pressure, sea level, river discharge

Advantages of instrumental records

High frequency, continuous, exactly dated, accurate

Main limitation of instrumental records

Short time span (mostly since mid-19th century)

Why are instrumental records insufficient alone?

Cannot capture full natural variability

What are documentary records?

Human-made records used to infer environmental change

Examples of documentary records

Diaries, maps, photographs, agricultural records

Advantages of documentary records

Extend further back than instrumental records

Limitations of documentary records

Subjective, geographically uneven, require careful interpretation

Why may documentary records be biased?

Focus on extreme or notable events

What are natural archives?

Natural sources storing past environmental information

Examples of natural archives

Ice cores, sediments, corals, tree rings, speleothems

What is a proxy?

Indirect measure used to infer environmental conditions

What proxy is this natural archive measure for? - oxygen isotopes in ice cores

Proxy for air temperature

What proxy is this natural archive measure for? Example: fossil pollen

Proxy for vegetation

What proxy is this natural archive measure for? Example: foraminifera

Proxy for sea surface temperature

Advantages of natural archives

Long-term records, show full natural variability

Limitations of natural archives

Dating uncertainty, low resolution, difficult interpretation

Why is dating natural archives important?

To determine timing, rates, and cause-effect relationships

How do frequency and magnitude of ecological change vary

Depend on timescale

What is the typical climate pattern over long timescales?

Slow cooling followed by rapid warming

Main elements in the universe?

Hydrogen and Deuterium

What is nuclear fusion?

Hydrogen atoms combine under pressure to release energy

How are heavy elements formed?

Supernova explosions

Solar composition (main elements)

Hydrogen (~91%), helium (~8.6%)

Solar Nebula Theory

Solar system formed from collapsing gas and dust cloud

How do planets form?

Condensation of elements into aggregates

Estimated number of planets in universe

~200 billion

What happened during early Earth cooling?

massive volcanic outgassing → volatiles released into atmosphere

created the planet's first stable atmosphere and oceans

What is the Earth’s Structure

Inner core — Solid metal

Outer core — Liquid

Mantle — Solid

Crust — Outer layer

When and how did the Moon form?

~4.5 billion years ago

"Giant-Impact Hypothesis"

a Mars-sized body named Theia collided with the young Earth

ejecting a massive amount of molten debris into orbit that eventually coalesced to form the Moon

Why is the Moon important?

it stabilises the Earth

Primary seismic waves vs Secondary seismic waves

Travel through solids and liquids vs Travel only through solids

Continental Drift

19th Century Edward Suess and 20th Century Alfred Wegener - Proposed that the continents had moved

What generates Earth’s magnetic field?

Movement of liquid metal in outer core - > Nothing to slow it down - in a vacumm, no friction -> creates magnetic field

How does the earth’s magnetic orientation vary over time?

Secular variation

Polarity reversals

Why does Venus lack a magnetic field?

Because it spins round once a year, angular momentum is really small

Types of plate boundaries

Constructive, destructive, conservative

Constructive boundary

Plates move apart

Destructive boundary

Plates collide/subduct

Conservative boundary

Plates slide past each other

Density of mantle vs water

Mantle is 3.3 times denser than water

Does oceanic or continental crust subduct? and why

Oceanic crust, it is denser

What is the geological timescale?

Division of Earth’s history based on rock record

Largest unit of time and smaller divisions

Eon

Era, period, epoch

What are isotopes?

Diff forms of the same element with diff masses

What are stable isotopes?

Isotopes that do not undergo radioactive decay

Why are isotopes useful in palaeoclimatology?

Their relative abundance in materials reveals past environmental processes.

What are the three stable isotopes of oxygen?

16O, 17O, 18O

Which oxygen isotope is the most abundant?

16O (>99%)

Which oxygen isotopes are most commonly used in palaeoclimate studies?

16O and 18O

Where is oxygen analysed in palaeoclimatology?

In water (H₂O) and calcium carbonate (CaCO₃).

Where can calcium carbonate (CaCO₃) be found in geological records?

In sediments and shells of organisms

What provides information about past climates in isotope studies?

Variations in isotope abundance

What isotope ratio is commonly measured?

18O/16O

What instrument is used to measure isotope ratios?

Mass spectrometer

Why are absolute isotope ratios rarely used?

They are very small and difficult to measure accurately.

What is delta notation? and in what units is it expressed?

The difference between a sample’s isotope ratio and a standard

Parts per thousand (%)

What does a δ18O value greater than 1 mean?

The sample has a higher 18O/16O ratio than the standard

What does a δ18O value less than 1 mean?

The sample has a lower 18O/16O ratio than the standard

What does a δ18O value of zero mean?

The sample and standard have the same ratio.

What standard is used for water and carbonate samples?

VSMOW (Vienna Standard Mean Ocean Water)

VPDB (Vienna Pee Dee Belemnite)

What do oxygen isotopes in ice cores mainly reflect?

Temp of precipitation

What happens to heavier isotopes during condensation?

they are removed preferentially from the atmosphere

What happens to remaining water vapour after condensation?

It becomes depleted in 18O

How does temperature affect isotope fractionation?

Lower temperatures increase condensation and isotope separation.

What is the relationship between δ18O in ice cores and temperature?

Positive correlation

Why are ice-core δ18O values useful?

they act as paleothermometer

What is the relationship between water temperature and δ18O in carbonates?

Negative correlation

What organisms are commonly used in deep-ocean isotope studies?

Foraminifera

What happens during evaporation in oceans?

16O is removed

What happens during glacial periods (oxygen wise)

Ice sheets grow and store 16O, thus becoming enriched in 18O

What do high δ18O values in deep-sea carbonates indicate?

Increased global ice volume

Why are lake isotope records harder to interpret?

More factors affect lake water composition

What influences δ18O in mid-latitude lakes?

Rainfall δ18O and water temperature

What is radiocarbon dating used for?

Dating carbon in Quaternary sediments

What is the max age range of radiocarbon dating?

40,000 - 50,000 years

Why is radiocarbon dating limited?

It only covers a small part of the Quaternary

What isotope is used in radiocarbon dating?

Carbon-14 (¹⁴C)

How is Carbon-14 (¹⁴C) produced? and what happens to it after?

Neutron bombardment of atmospheric nitrogen by cosmic rays

It oxidises to ¹⁴CO₂ and enters the biosphere

What are the two main causes of long-term variation in atmospheric ¹⁴C?

changes in production rates

changes in reservoir exchange

How do geomagnetic changes affect ¹⁴C production?

Weaker magnetic field allows more cosmic rays → more ¹⁴C

How does solar activity affect ¹⁴C production?

Low solar activity → more cosmic rays → more ¹⁴C

What is the relationship between sunspots and ¹⁴C?

Low sunspots → higher ¹⁴C and cooling

High sunspots → lower ¹⁴C and warming

How does ocean circulation affect atmospheric ¹⁴C?

Changes alter exchange between ocean and atmosphere

What is the role of ocean circulation in ¹⁴C storage?

It transfers ¹⁴C to the deep ocean

How does volcanic activity affect ¹⁴C levels?

Adds CO₂, diluting atmospheric ¹⁴C concentration

What is short-lived radioisotope dating used for? why is it impt? what materials can be dated using this method?

Dating very recent sediments (last ~100–130 years)

It allows study of post-industrial environmental change

Marine sediments, lake sediments, ice cores

How is Lead-210 (²¹⁰Pb) produced? how does it enter sediments? what is it used to determine?

From the decay of Radon222 in the atmosphere

Deposited onto land/water and incorporated into sediments

Determines sediment age and sedimentation rates

What is Caesium-137 (¹³⁷Cs)? when was its peak and secondary peak

An artificial radioisotope from nuclear weapons testing and reactors

First peaked in 1963, then in 1986 (Chernobyl)

What is a radiometric sediment core and what does it show?

vertical samples of lake or ocean floors analyzed for radioactive isotopes

Age, sedimentation rate, and isotope concentration with depth