Investigating the Past

what are the core ‘drivers of change in the earths system

changes in plate tectonics, earths orbit and sun’s strength

age of earth

4.5 billion years

late cenozoic ice age

ice age we are currently in began 34 mill years ago, currently in warmer interglacial period known as the holocene which began around around 11,000 years ago

cenozoic ice age

started 65 million years ago and it involved the gradual cooling over the geological time resulting in the formation of glaciers (around when the dinosaurs died out) 

instrumental records

most extend back to mid 19th centuary, many much shorter

• Direct measurements of environmental variables that are made with instruments (often made at high frequency, daily or even hourly). 

• Meteorological variables are obvious examples but there are others (sea level, river water discharge and quality...) 

• accurate if date+time also recorded(baso no dating uncertanties)

• high resolution

• largee geographical ‘gaps’

documentary records

• Extend the timescale beyond that of instrumental records, but still limited in time span 

• Geographically restricted 

• Require caution in interpretation 

• May highlight examples (might assume a very cold winter is just the average winter) 

• May involver subjectivity (observer dependent) in recording and anecdotal evidence 

• Eg. Inscriptions, Paintings, Maps and charts, Agricultural Records, Diaries, Photographs... 

• (Glaciers are very good measure of changes in temperature and precipitation) 

• Documentary records allow us to extend further back into the past than instrumental records (e.g. up to 1000 or even 2000 years in the case of archives from China).

proxy records

derived from natural archives . indrecte evidence

natural repositories of info ab past climate

• Eg. Sediments (Marine sediments of Terrestrial sediments), Ice, Corrals, Trees... etc 

a paleoenvironent poxy

is a measure from a non0natural archive that is used a proxy from some climate, climate-related or environmental variable that cannot be measured directly. 

include rock and sediment records, cores of ice from ice sheets, tree rings and speleothems (stalagmites and stalactites in caves).

Proxy evidence used to reconstruct ancient environmentst

long term records requiring interpretation

can extend fra back

iisues with paleoenvironmental proxy evidence

• It may be difficult to produce quantitative estimates of past environment. 

• Often difficult to establishes seasonality 

• Dating may be uncertain

• may be hard to interpret

what must natural archives be

dated (instrument+documentary evidence has an age assigned to it)

order of geologic timescale

cenozoic, mesozoic(dinosaur era), plaeozoic, precambrian

what are we currently in

cenozoic, glacial, holocene

dating with the geologic time scale

‘a’ refers to age • ‘y’ or ‘yr’ to duration • Prefix ‘k’ = thousands (kilo, or 103) of years (k is lower case - K is the Kelvin) • Prefix ‘M’ = millions (Mega, or 106) of years (M is upper case - m is milli, or 10-3) Examples • 10 ka =10,000 years ago • 2.4 Ma = 2,400,000 years ago • 10 kyr = an interval of 10,000 years duration

disagrams concerning the geologic time period will have age meausred in what on graphs

(a) (Ma) (ka) (ce)

palaeoenvironmental proxy:measure/archive/proxy

does frequency and magintude of change vary with timescale

yes

order of geographical timescaless

eon>era>period>epoch>age

what eon are we currently in

The Phanerozoic Eon
Started 541 million years ago and includes most visible life.

what are the 3 eras in the phanerzoic era

cenozoic startinf 66 million years ago age of mammals

mesozoic starting 252 million years ago age of dinosausr

palaeozoic 541 million years ago ancient life

which era is known as the ‘age of the dinosaurs’

mesozoic

• 3 periods: cretaceous, Jurassic, Triassic

What event marks the end of the Mesozoic Era?

The Cretaceous–Paleogene extinction event
(~66 million years ago) which wiped out most dinosaurs

2 periods in the cenozoic and which are we currently in

Quaternary (in) 2.58 milll years afo

Tertiary 66 mill years ago

order of tertiary epoch (most recent to least)

Pliocene

Miocene

Oligocene

Eocene

Palaeocene

order of palaeozoic periods(most recent to least)

Permian

carboniferous

devonian

silurian

ordodvician

cambrian

What do the age numbers on the geologic time scale represent?

The time in millions of years ago when a geologic boundary occurred

Paleozoic → Mesozoic → Cenozoic
Think: “Past – Middle – Current life.”

isotopes

different nuclides - forms of same elect w different masses

stable isotopes do not undergo radioactive decay

why are isotopes used in palaeoclimatology

different isotopes behave differently in the environment + relative abidance in geological material can therefore tell us about past processes

oxygen isotopes relative atomic mass

16 - 99.759%

17 - 0.037%

18 - 0.204%

which are most used in palaeoclimateology

16O and 18O

how are oxygen isotopes used in palaeoclimateology

analyse the oxygen that is part of the water molecule (H2O), for example in ice cores, or in calcium carbonate (CaCO3) preserved in sediments as chemical precipitates or in shells of organisms.

relative abundance of diff isotopes (ratio)

measured using a mass spectrometer

act as palaeothermometers (past temperature indicators)

why are absolute ratios rarely reported + what is used instead

• They are very small numbers

• Difficult to measure accurately

• Hard to work with mathematically

Delta (δ) values, which compare the sample to a standard.

What does δ¹⁸O represent?

The difference in ¹⁸O/¹⁶O ratio between a sample and a standard, expressed in parts per thousand (‰).

• expressed In parts per thousand as isotope differences are very small

• mainly use this as rare+ heavy therefore can compare to common

What standard is used when analysing water samples?

VSMOW (Vienna Standard Mean Ocean Water).

What standard is used when analysing calcium carbonate?

VPDB (Vienna Pee Dee Belemnite).

What does a δ¹⁸O value greater than zero mean?

The sample has more ¹⁸O relative to the standard.

if 0 = same

if less = less

Where are most ice cores used for oxygen isotope analysis taken from?

greenland and antarctica

What mainly controls δ¹⁸O variations in ice cores?

Temperature of precipitation (snowfall).

Why are heavier water molecules (H₂¹⁸O) removed from the atmosphere first during condensation?

Because heavier molecules condense more easily.

therefore atmospheric water vapour levels;s become depleted in O18

cold temps increase condensation+ enhance o18 removal

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

A: Positive correlation (higher δ¹⁸O = warmer conditions).

What two main factors control δ¹⁸O in carbonates?

Water temperature (neg correlation, warm water lower 18o)

δ¹⁸O of the water(positive correlation, highr carbonate

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

Foraminifera (microscopic organisms with calcium carbonate shells).

RECORD 18O. values mainly reflect changes in ocean ocean water 18o which linked to global ice volume

Why does ocean δ¹⁸O increase during glacial periods?

When seawater evaporates, H₂¹⁶O evaporates more easily. During glacial periods this light water becomes stored in ice sheets, leaving oceans enriched in ¹⁸O, increasing ocean δ¹⁸O.

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

Large global ice volume (glacial conditions).

Why are lake carbonate δ¹⁸O records harder to interpret than ocean records?

Because lake water δ¹⁸O is influenced by many factors, including:

• Rainfall δ¹⁸O (often linked to air temperature)

• Water temperature

• Evaporation (which removes ¹⁶O and increases δ¹⁸O)

Proper interpretation requires understanding the specific lake system.