and his young daughter Maria explored a dark cave in Northern Spain.

When Maria wandered off by herself, she made an amazing discovery.

They were standing inside a site of ancient art,

the walls and roofs decorated with prehistoric paintings and engravings,

ranging from 19,000 to 35,000 years old.

Similar marks of our ancestors have been preserved in caves all over the world.

The oldest we've found were made up to 40,000 years ago.

What do these images tell us about the ancient human mind

and the lives of their creators?

These early artists mixed minerals, clay, charcoal, and ochre with spit or animal fat

to create paint.

They drew with their hands and tools, like pads of moss, twigs, bones, and hair.

In many instances, their images follow the contours of the cave

to create depth and shade.

The most common depictions are of geometric shapes,

followed by large mammals, like bison, horses, mammoths, deer, and boars.

Human figures appear rarely, as well as occasional hand prints.

Some have theorized that these artworks are the creation of hunters,

or of holy men in trance-like states.

And we've found examples created by men, women, and even children.

And why did they create this art?

Perhaps they were documenting what they knew about the natural world,

like modern scientists,

or marking their tribal territory.

Maybe the images were the culmination of sacred hunting rituals

or spiritual journeys.

Or could they be art for art's sake, the sheer joy and fulfillment of creation?

As with many unsolved mysteries of the ancient world,

we may never know for sure,

barring the invention of a time machine, that is.

But while the answers remain elusive,

these images are our earliest proof of human communication,

testifying to the human compacity fo creativity

thousands of years before writing.

They are a distinct visual language that imagines the world outside the self,

just like modern art forms,

from graffiti and painting to animated virtual-reality caves.