How to add BC-dates (age of a continent)

Seems like temporal controler only works with standard dates. If you dont mind cheating a little you can create pseudo-standard-dates out of your real dates. So e.g. 1000000 real years become 10 years for QGIS temporal controler.

For this to do, you need to know a suiting divisor for your date, you can find out by looking at your max and min value. In my example I am using 100000 having a max-real-date of -1000000 and a min-real-date of -20000000. So 1000000 real years become 10 years for QGIS temporal controler. Just use make_date() expression like this to create your pseudo date: make_date(round(abs("integerfield")/100000),1,1).

Use it within temporal settings of your layer as expression:

Here a comparison between the two fields when using the above expression:

As animation it can look for example:

PS: no guarantee here that I did not mess up with zeros.

The time manager plugin has an "Archaeological mode" (tiny button left of the setting button) that let you use negative date.

This plugin won't work with the latest QGIS release (the native temporal controler replace it since version 3.14, ) but you could use an older QGIS version or have a look at how the plugin handle negative date...