What percentage of geologic time have humans been around for?

About 0.1 to 0.2%

Explanation:

The geological time scale can be defined as the arrangement of major events that has taken place on earth, right from the time of formation of the earth, which is about 4.6 billion years back.

According to this time scale, the humans have appeared in the Cenozoic era, some 7 million years back from the present. This is comparatively very recent.

So, from this, it can be concluded that the humans have been on earth for about 0.1 to 0.2% of the total geological time scale.

they use tree rings to figure out weather patters.