Earlier and later posts link at bottom of page

I apologize if this question has already been asked and answered, but I was unable to find it in my search.

I would like to add a link to earlier posts at the bottom of my blog, so that readers can continue reading in reverse chronological order. Right now, when they hit the bottom of the page, they can only read more by using the archives or categories, which is not the most efficient way.

Do I need to tweak the code or add a plugin? Or are there some themes that support this and others that don’t? I’m currently using K2 on http://popvultures.com.

Thank you for your help.