Many historians think they don’t need to understand archaeology to understand history. Who needs objects when there are written records anyway? But the further back in time we study, the fewer records survive, and to understand prehistory – which by its very name means there are no written records of it – archaeology becomes extremely important. At the very least, seeing objects connected with the past can make that past seem more real and can make it come alive. That’s why people like visiting museums or historic places such as Stonehenge. Sometimes though, the things archaeologists discover change the way people think about the written records, and can make them change their mind about what actually happened. The word ‘archaeology’ comes from the Ancient Greek for learning about ancient things, but now it means the study of the human past through the objects left behind. It doesn’t study dinosaurs or other ancient creatures that lived before the first human-like species (that’s what palaeontologists study), and nor does it study rocks (which geologists look at). Most think of archaeology as simply digging up bits of old pots, but it covers a broad range of areas, from underwater archaeology to studying satellite photographs. Scientific processes have been applied to it to help provide information on everything from the diet of early humans to where humans came from. As we think archaeology is important for our understanding of history and mention it a lot on this site, here is a brief guide to some of the main things that archaeologists do.

Fieldwork

This is what most people think about when someone mentions archaeology: it is the hands-on act of finding a site, digging it, and collecting what’s dug up. Archaeologists have to be careful not to contaminate the evidence by, for example, getting it mixed up with other finds that may come from different layers or parts of the dig, or by introducing something that shouldn't be there (such as an old coin slipping out of their pocket). They also have to make sure they record everything properly, so that other people can see what they found, where they found it and how they found it. There are tools which archaeologists use to help them decide where to dig. These include:

• Aerial photography – where people in planes take pictures of the land. From this, they can see any unusual bumps or other markings that people on the ground might not be able to see.
• Geophysical surveying – uses technology to see what’s under the soil, by measuring whether it is more solid in some places than others, or whether there is anything magnetic in it. It is done by walking the equipment up and down in a grid-like pattern, and then looking at the results.

Dating

An item can only be useful if we understand something about it. The most obvious thing to find out is how old it is. If we’re lucky, then the item (such as a coin) might be datable from what we know about history. However, most of the time, an object is not stamped with a date, and we need to find another way of dating it. There are several ways to do this:

• Relative dating – this is saying whether something is newer or older than something else. It works on the principle that things found deeper in the soil are older than things that are closer to the surface. It can also be done by grouping an object with similar ones (for example, styles of pots change over time so we can find out something about that pot by comparing it with others). None of these methods give an actual date, only where a find will sit compared with other finds. It is not accurate and can be misleading.
• Dendrochronology – or tree ring dating is based on the fact that trees grow at different rates each year depending on the weather, but each year a tree will always add another ring. Because archaeologists can have access to very old wood, they can produce accurate dates for objects made from wood, sometimes going back 10,000 years, although some trees preserved in bogs in New Zealand are up to 40,000 years old.
• Radiocarbon, or carbon dating – this is the most well-known way of dating organic objects (things such as plant or animal remains, that were once alive). When things are alive, their bodies absorb an isotope called carbon-14 from the Sun. When they die, they stop absorbing it, and the carbon-14 starts decaying. Archaeologists can work out how long something has been dead by how much carbon-14 is still in the body. However, these results need testing against other ways of dating (‘calibration’) to make sure they are right, because the amount of carbon-14 in the atmosphere can change over time. This form of dating works up to about 50,000 years ago at most.
• Potassium/Argon dating – is used to date rocks in volcanic areas, and works in the same way as carbon dating, by measuring how much potassium-40 there is, compared with argon.
• Thermoluminescence – is used to date pottery and burnt flint (anything that hasn’t been alive, but that has been exposed to heat or sunlight) that has been used within the last 10,000 years.
• Electron Spin Resonance – is used to tell how old human or animal teeth are if they are older than 50,000 years (and can’t be radiocarbon dated), by measuring changes in electrons (some of the small particles which form all matter on earth) over time.

Experimental archaeology

Even when archaeologists have all of the items they can find, they still don’t always know what they were used for or how they were made and used. This is where experimental archaeology helps. Experimental archaeologists take the tools (or make replicas – new ones modelled on the old ones) and try to use them. This can tell us a lot more about the skill of the people who used items, as well as a bit about how they actually lived.

Chemical analyses

As well as those tests that are done to date archaeological finds, chemical tests can tell us other things. In particular, it can tell us where and how people lived.

• Tooth enamel is a very hard substance, which is grown while we are young, and it can be tested to tell us something about the person who owned the teeth, as teeth absorb the things we eat and drink. If we drink water in a colder climate, then that water will contain more of the isotope oxygen-16 (which is the most common oxygen isotope), but if we drink water from warmer climates, we will find more oxygen-18. So, a person’s teeth can tell us if they grew up somewhere hot or cold. Also, a chemical called strontium is absorbed into our teeth through the food we eat, and different soils contain different levels of strontium. So, we know that the Amesbury Archer, who lived 4,000 years ago and died near Stonehenge, actually came from the Alps.
• Bones, like tooth enamel, also absorb chemicals (such as carbon and nitrogen) from the food we eat and these can be tested to find out what sort of diet a person had in the 10 to 15 years before the person died (so, whether food mainly came from meat, or from fish, or from plants). Strontium that is found in bones can tell us roughly where the person lived in the last 10 years of that person’s life.

DNA analysis

DNA is the genetic code within all living things, which biologically makes us who we are. It is given to a child by both parents, and can therefore tell its own story about the history of a family tree and of large movements of people (migrations). There are two main types of DNA analysis:

• Mitochondrial DNA – this is DNA that is passed down from a mother to her children, but is never passed from a father to his. Because it changes so little over time, it is possible to show a deep history of someone’s female line.
• Y chromosome DNA – If a person has a Y chromosome, they are male, and they have had the chromosome from their father. This means that the Y chromosome can be used to trace the male line back through time to find out where a person’s ancestors might have come from.

Digital archaeology

With improvements in technology, much work that used to be done over long periods by archaeologists out in the field is now being done on computers, with the help of enhanced photographing and scanning. The main ways this is being done are set out here.

• Laser scanning is expensive, but can show archaeologists carvings and other bumps in things which we can’t normally see.
• We can get a better idea of how things looked with the help of modelling from photographs. These models are three-dimensional (rather than flat pictures) and so give us a better idea of how anything solid might look.
• Photograph enhancement, or fiddling with digital pictures, can bring out aspects of that picture which the eye normally can’t see. This allows archaeologists to find more cave art, for example, and can also tell them what layer or painting was drawn first.
• Satellite imagery has taken over from the old aerial photography used by archaeologists to spot patterns in the land. With tools such as Google Earth, it is now possible to spot lots of archaeological features, and they can be almost anywhere in the world.

Things to do

• Lots of people find things in the ground using metal detectors, which can be bought reasonably cheaply. If you can, use a metal detector to do some geophysical surveying of your garden or a local field (be sure to ask the farmer’s permission first!).
• Look at samples of wood and see if you can see the rings left by the tree’s growth. Look at the sizes in the different layers and come up with the story of the weather during the tree’s lifetime
• Try extracting your own DNA:
  1. Rinse your mouth out with 25ml of water and a pinch of salt (careful not to swallow any!) and spit it into a container
  2. Put 1ml of washing up liquid and 6ml of pineapple juice in to the container and shake it (preferably with a lid on!)
  3. Strain the mixture into another container
  4. Pour 60ml of alcohol (of about 80-90% ABV – parents can buy something like overproof vodka or rum for this part) on top of the mixture
  5. Your DNA will separate from the mixture in the bottom and rise into the alcohol to form a cloud.

• ‘Living history’ events show the public how experimental archaeologists work, and are common during the summer particularly at historic sites. It’s always fun to spend a day visiting one of these, or going to year-round attractions such as Butser Iron Age Village, or Blists Hill Victorian Town.
• The Council for British Archaeology holds a festival once a year, with archaeological events up and down the country. There’s always a chance to try a dig or experimental archaeology somewhere local. See information about the next festival at http://www.archaeologyfestival.org.uk/
• Use Google Earth to spot some archaeological features near you and in other countries.