1 Flashcards
What is the Quaternary?
The most recent period of the geological record extending to the present. It is climatically, sedimentologically and ecologically distinct from earlier periods, and has had variable warm and cold cycles.
When did the Quaternary start?
It is internationally recognised as starting at 2.588 +/- 0.005 million years ago. (Gibbard et al. 2007).
What is the Holocene?
The current warm period within which major human development and modification of the Earth has taken place. (Last 10,000 years of Quaternary).
Evolution of Ideas of Earth’s Past Environment
James Ussher (16th Century) concludes Noah's flood created the Earth we see today. Lyell (18th Century) Argued observable geological processes could explain geographical history. Hutton (1726-97) observed rocks are constantly renewed and recycled, envisaged there was no begging or end, everything is explainable by processes currently operating on Earth. (Uniformitarian Theory).
How do we reconstruct past events (simple)
We need to find evidence, understand these and their distribution to reconstruct the past.
Huttons Maxim
The present is the key to the past.
What is ‘proxy data’ or ‘proxy record’
An indirect measurement of climate or environmental evidence.
What is a modern analogue?
This is how you unlock a proxy record by looking at modern processes or distributions etc.
‘When knowledge of a current system/process is used to interpret proxy data for past conditions, we are treating the current system/process as an analogue.
What does the use of a modern analogue assume?
- The same processes occur today in the same way as they did in the past.
- Through the quaternary, plant / animals haven’t evolved/adapted to different conditions.
- ‘all other things being equal’ e.g. assuming tree rings are dominated by climate cycle, not squirrel population.
Key assumptions of Uniformitarianism (these underpin the use of proxies and analogues)
- Controlling environmental factors are known (if beetle is temp sensitive or veg sensitive).
- Ecological affinities remain constant through time (dung beetle always ate dung)
- Populations past and present are/were in equilibrium.
- Modern analogues exist for past species/environments.
- Process of fossilisation (taphonomy) is known.
- No contamination or differential preservation.
- Fossil species can be identified.
Sources of Evidence
Glaciological (ice cores) Marine (sediment cores) Terrestrial (landforms, sediments). Biological (tree rings, insects, fossils). Historical (images, documents).
proxy conditions we can interpret from evidence
Temperature Precipitation Flows (atmos, ocean, ice) Events (timing & magnitude) Relationships between events (correlation)
Advantages of Oceanic Evidence
- Long records, continuous deposition means no gaps.
- Several different lines of evidence
- Reflects global hydrological and temperature changes,
Disadvantages of Oceanic Evidence
- Can lack spatial detail.
- Low temporal resolution (sedimentation is very slow as little as 1cm/1000yrs)
- Cant identify short lived events.
- Time and money consuming
Advantages of terrestrial Evidence
- Many different lines of evidence across multiple disciplines.
- Plenty of evidence (geomorphology, sediment, biological)
- Can reconstruct different elements of climate change, temperature, wind, precipitation etc.
Disadvantages of terrestrial evidence
- Temporal and spatial discontinuity due to erosion (except ice core records).
- The best records may only cover short time periods.
- Lack of good analogues.
What makes a good proxy?
- Good time span
- Real representation
- Continuity
- Un-ambiguity
- High sensitivity / fast response to climate change.
- Dating control
- High resolution
- Low cost
Why do environmental reconstructions use multiple proxies?
Most proxies only meet a few of the ‘good proxy’ criteria, so we use multiple to combine their interpretations, and use different dating methods for verification of a reliable picture of the past.
How can lag cause issues when comparing proxies?
Different proxies can have different lag times to respond to climate change. E.g. Coleoptera records may respond quicker to climate change than tree-pollen count, hence we must consider lag times when reconstructing the past.
What is relative dating?
This type of dating compares whether something is older or younger than something else. This is powerful as it places events/sediments in order, on an ordinal scale.
What is incremental dating?
This is when we know the rate of change per year, e.g. one tree ring grows per year, from this we can measure how many events have occurred and get an idea of the age of something. E.g. A tree with 100 rings we know is 100 years old.
What is numerical/absolute dating?
This produces the years of when an event occurred in the past, including luminescence and carbon dating. However there is usually some uncertainty within the result.
What are the two principles of relative dating?
Relative Position: based on stratigraphical principles, oldest sediment at bottom, youngest at top. E.g. Lancaster et al., 2002 confirmed subsequentuality of overlapping dunes in Western Sahara, using luminescence dating.
Relative change is based on physical and chemical changes, e.g. soils weathering. You can compare rocks with the same geology but different erosional features to get a sense of change and age.
What is a floating chronology?
A chronology of events that have been relatively dated, but there is no identified start or end point. An example would be if you aged a tree that had been cut down but didn’t know when it was cut.
