Eli5 How did ancient drawings in caves survive thousands of years without wearing away completely?
In: Earth Science
Caves are protected environments. No wind, no water, few animals. The cave drawings that survive are generally in very isolated , deep parts of caves where’s there even less of those factors.
Prehistoric people probably drew lots more stuff in lots more places, but those places would be more affected by erosion, weather, animals, and later populations
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There were even “cave galleries” where only respected artists would be allowed to paint on the wall. Like the Chauvet Cave in France. https://en.m.wikipedia.org/wiki/Chauvet_Cave
Some really advanced techniques were used to create these drawings too, for example using the unique shape of the walls to create interesting effects of perspective.
Researchers couldn’t figure out why many of the animals seemed to have more then 4 legs, some with 6 or 7. It was then suggested that if viewed by a flickering firelight it would create a visual illusion of movement
>How did ancient drawings **in caves** survive thousands of years without wearing away
In a cave, what’s going to wear them away? Most weathering processes don’t exist in caves (light, wind), that’s why they’re good dwellings.
**More importantly**, there’s a huge survivor-bias here. All we have to go on are ones that DID survive. There’s no way to know how many more there were that DID wear away completely. Of course there’s still some weathering in caves, from water, crumbling walls, moss/mould, maybe animals. But any of the ones that eroded are gone, just like you said! When we find cave drawings that survived 1000s of years, that’s the 1% of initial drawings that happened to be in suitably dry, dark, stable caves. The vast majority didn’t make it.
It’s like how we think “wow old machines really were built to last”. Partially true, but also most machines of the 50’s were in landfills by the 60s, and the 50s machines still in use today are the 1% that didn’t break, *and* got super well maintained.
1. Very little erosion since it’s in a cave.
2. The use of oxides for painting. For example, the ochre which is one of the most common pigments (in red, browns and yellows) is basically iron oxide. Since it’s an oxide it can’t oxidize.
3. No sunlight. Being in a cave the paint isn’t exposed to the bleaching effect of the sun (light, and especially UV radiation, will break down most pigmentation bonds over time. For example the US flag on the moon is almost certainly pure white by now).
4. What little rainwater that seeps down will actually act as a preservative. Travelling through the rock the water will carry with it hydrogen carbonate (HCO3) which leeches off as it travels down the rock wall and forms a protective glaze over the painting and protecting it from future erosion.
Basically a cave is the perfect preservation environment for a wall painting because of the lack of outside influences like temperature drops and spikes, wind, water and very few animals. This is the same reason why bones and other remains found in caves are often in very good shape for being tens of thousands of years old.
All of the answers so far focus on how caves are protected environments. My answer focuses on something else.
The question you posed already bakes in a bunch of survivorship bias. The ancient drawings *we have found* were found because, well… they survived. The more general question might be why do some ancient art survive while others didn’t and what blind spots does that create in our understanding of ancient art?
Lots of ancient (using the term loosely to span from prehistory through classical antiquity) art was lost because it was done without durable media (e.g. bright colors on Greek marble busts), were in sites subsequently obscured by natural elements (Maya pyramids, Nazca lines, anything in the Sahara), were destroyed by humans (Tadrart Acacus carvings), or other reasons.
Think of writing something on paper. Inside your house that paper is going to be fine. It’ll sit on the table and just kinda be looked at. But bring it to the beach and leave it on the sand without touching it. It’ll get dirty buried in the sand by the wind, maybe even taken out to ocean if the tide comes in.
The difference is inside away from the elements that paper is protected, but outside many things can happen that would destroy it or cause you to lose it.
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