Randall Munroe has done it again. His latest xkcd comic is an enormous timeline of the Earth's temperature, showing the enormously long time we have temperature estimates for, and how little it has changed until very, very recently.
Munroe has an incredible talent for creating simple and fun explanations for complex topics. I highly recommend his book, Thing Explainer.
The comic is a great example of not constraining yourself to some predefined format, but instead finding the right frame for what you're trying to show. In this case, the image is about 750px wide and almost 15,000px high: an aspect ratio of 20:1.
And since Munroe encourages embedding and hot linking, here's the whole thing in all its glory: