I like David Talbott's explanation. It could be something they saw in the sky.
https://www.youtube.com/watch?v=PmropNlSRdE
Skip to the 19:00 mark to see the same drawing depicted worldwide. It's the same shape you get with super heated plasma in a vacuum.
https://www.ancient-origins.net/sites/default/files/field/image/petroglyphs.jpg
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