how do archaeology digging not damage artefacts or fossils?

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Everytime I see clips of these archaeologists dig stuff, I can’t help but wonder how do they know where or when to stomp their shovel into the ground? It seems to me that if you aren’t for certain, your digging could easily damage or break a potentially great discovery.

I’ve seen anything from shovels to excavators and they seem to go pretty hard into the dirt.

So how do they know how much force to hit and make sure they don’t cut or destroy such ancient and delicate items?

In: Earth Science
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Initial discoveries can be made by normal construction activity that obviously is done with excavators and shovels, but when archaeologists are digging in an area known to contain artifacts they do their preparation. Dirt layers build up over time, so when something is uncovered say 3m underground they will look at the layers above in the area already exposed to see what was going on during those periods and if it is of interest. After checking a number of spots they gain confidence that indeed the area of interest is covered by 2m of overburden and they can use equipment to remove that material more efficiently than the hand trowels, brushes, and fine picks used for the delicate work.

Scientists use ground penetrating radar and sonar as well as geology to get estimates on how deep the site is. They then go through all the material with a fine tooth comb as they dig and switch to very delicate methods once close to where the artifacts should be.

There are many techniques that can be loosely categorized as invasive (using an excavator), minimally invasive (manually troweling) and noninvasive (ground penetrating radar). The selection of excavation technique depends on the initial information gathered about the site locality and what is feasible for the project in terms of money and time. Different archaeologists in different areas of the world have different excavation preferences based on their research topic and geographical area. Mistakes unfortunately do happen, but when the research is important to society, it is unusual that the artifacts are not handled with care.

There are layers in the ground called strata, and we usually know which one we’re looking for.

So if you’re looking for a load of burials, and there are 3 strata, you know that layer 1 is soil, layer 2 is pebbles, and layer 3 is clay. The people lived before the soil, so they lived on layer 2, but they dug the graves deep down so the holes for the people will be in layer 3, so you can remove all the soil and some of the rocks with a digger and then be really careful with the clay layer.

Saying that, on a dig in Spain, the first hit with a pickaxe into the top layer shattered a burial urn, the head archaeologists response was just “that’s what glue is for!”. Once you find the right layer you do everything super slowly. So when I found the edges of a burial hole with my shovel, I dug with a tiny trowel and brush, and every inch or so was photographed and cataloged, so you couldn’t do any damage. All of the dirt that was dug out was inspected and even tiny bone fragments were sorted and kept.

Usually diggers are used to remove all the layers that people have already messed with. Farmland has been plowed to a certain depth, so you know everything up to a certain point has been disturbed anyway.

Whatever was protecting the artifacts or fossils from the elements would protect it from the slow process of digging. Also, the people who dig a site have some idea of what could be buried there