PR has nothing to do with your adsense performance. So don't worry, changes in PR won't make any difference in your earnings. SticKer
PR is no way related to your adsense earnings. PR is important when you are looking to sell text links as well as sponsored posts on your website.
Why would PR matter when trying to sell text links? (I'm going somewhere with this question so consider the answer...) ie, what is it about the PR that is enticing to the person who is buying the link?
I am not google that can answer directly on your question but pr is also a googles product. So who knows that big G also get some points on this. This is only my opinion. What do you think?
Most people are saying that PR not effect AdSense earning. But, I want to say it affect AdSense earning not directly but indirectly. Page rank is a numeric value given by Google to a website based on the importance of the page on the internet. So, if you have PR blog means you are getting more organic traffic better than PR0 blog. So, your CTR rate will be high and you will get more adsense revenue.
I'm not seeing that It's related. But I have some experience that if You have a good PR, google is placing good paid ads as well as They think your site is trustable.