Time-Traveling Pentagon

I was just staring at the pentagon for a few seconds, and then all of a sudden it disappeared. About a minute later I got this picture and a letter.


Here's the letter:

Dear Ben,
I decided to travel back in time. I'm in the Ice Age, apparently. It's pretty cool (get it?). Here's a picture of me with a woolly mammoth.

I don't know if I'll come back. It's kind of boring in your time. Here we have mammoths. Also, I don't know how to get back. Maybe you should have invented me with some sort of chronometer so I could control my time travel.

I'll probably see you again, though. I believe I'm immortal, but that has yet to be proven. Look over your shoulder--am I there? [He wasn't.]

Anyways, I hope you're not mad at me. But if you are, it's not like you can do anything about it.

Sincerely,
Infinity Pentagon

At least that was nice of him to send something. Still, I'll probably have to invent another time-traveling pentagon to find him and destroy him.