Anthony Peratt authored this paper in 2003 that strongly correlates the existence of many similar petroglyphs (worldwide) from antiquity to substantially higher auroral activity (i.e... a more energetic sun).

It's a solid paper; Peratt created many different plasmas in the lab and showed their distinct similarities to early petroglyphs.

Is there a competing explanation for his observations? I did find a paper once that seemed to be trying to negate Peratt's work. If I remember right they correlated historical accounts and concluded that solar activity was probably much the same back then as it is now. I don't have a link for it but distinctly remember they never delved into "pre-history" as Peratt is doing.

If he is correct then the sun's relatively recent history was much more variable than we've thought.

We humans seem to have an ingrained need/desire to document the things we see. In our modern world we take pictures. In antiquity they scratched on rocks. I have read and reread Peratt's paper and I am unable to conclude anything other than that "Grog" (if you remember him) looked up and saw the very same patterns in the night sky that Peratt saw in his lab. And the next morning he documented it on his cave wall.

We are aware that the sun is not completely stable and even in the last 2,000 years there has been heat ages as well as periods of great cold. Material falling into it, like a large asteroid or even the solar system going through intergalactic clouds of dust and gas can make a difference too. As to our view of the sun with the unaided eye, that can change due to volcanic eruptions or large meteor impacts nearby.