In order to understand our present environment, and better predict future changes, it is important to analyse past records of environmental change. These records can provide long-term context for changes in the Earth’s system and are described by scientists as “palaeo-data”, where “palaeo” means past. This means that they can be either historical records (since written records began) or from before this, in pre-history (in other words, further back in geological time).
Historical records can include anything from ancient observations, such as an ancient diary entry documenting a flood event, to weather station data collected yesterday. For example, a great deal of our knowledge of the famous Mt Vesuvius eruption in 79 AD comes from a written account by Pliny the Younger, of Ancient Rome. Although many of these ancient sources are fragmentary, or based on the viewpoint of an individual, they help scientists to piece together past events in the Earth’s history. In more recent times, technology has allowed us to collect more detailed and continuous data, such as the weather data collected by the UK’s Met Office, or the monitoring of volcanoes before and during an eruption.
Using prehistorical records allows us to reconstruct longer-term past environments. The discipline of Geology focuses on prehistorical data throughout the history of the Earth (4.6 billion years). This section with focus on the Quaternary (the past 2.6 million years), though many of the techniques are also used for older geological records. The Quaternary is unique amongst geological time periods as it gives us the opportunity to study detailed, high-resolution and accessible records of environmental change. As it is the most recent geological period, the records of past climate change are comparatively well-preserved.
Quaternary studies focus on several different palaeo-records, including:
- Geomorphology: the interpretation of features in the landscape formed by rivers, glaciers and oceans, for example. Landforms are often made up of sediments, analysing these sediments can tell us about how the landforms were developed.
Sedimentology: the characteristics of rocks, sands and soils (collectively known as ‘sediments’). These can come from many environments including lakes, rivers, cliffs, peat bogs, ocean-floor sediments and glacial sediments. Analysing the ways these sediments were laid down tells us about the environment at the time of deposition.
Ecology: the study of fossil or sub-fossil organisms (palaeocology, palaeontology). These are found within sediments and can tell us about the past environmental conditions in that area.
One example of how we might study part of a landscape is within a lake sediment core.
The schematic below shows a lake basin surrounded by a landscape containing many varieties of trees and plants (vegetation). Much of the pollen from this vegetation will eventually be washed into the lake and deposited at the lake bed. Quaternary scientists take samples of the sediments at the bottom of a lake and assess its sedimentology. Lake sediments normally contain very fine silt and clay material and often sand and gravels (sediments). Within these sediments, macro- (visible to the eye) and micro- (visible under a microscope) fossils are often well-preserved. These fossils are ecological indicators and represent the organisms that were living in or near to the lake at the time that they were deposited at the lake bed. By studying them at the present day, we can understand what the environment was like hundreds or thousands of years ago.
The palaeo-records can tell us a great deal about the type of environment under which they formed.
But how do we know when these climatic regimes existed?
How can we be sure that we are analysing a climatic period from thousands of years ago rather than a hundred years ago?
In palaeo-environmental studies it important to use dating techniques to gain an absolute age on the landform/deposit/fossil under investigation. This is done using a range of methods such as: radiocarbon dating (14C); Uranium-series dating; cosmogenic dating; or luminescence dating. Many of these techniques involve measuring the levels of naturally occurring radioactive isotopes that are round within rocks, sand grains or biological material. They are often time consuming or expensive methods, but form an important part of palaeoenvironmental research. Only by dating climatic events as accurately or precisely as possible can we fully understand the ways in which the Earth’s climate has changed over time.