Why does the iCal app on my MacBook Pro only have a 2-year archive? Where did everything before that go? And can I get it back?

I use my iCal as a daybook and every now and again need to reference events or occurences from several years ago. I tried to look something up from back in 2010 and the iCal on my MacBook Pro only has iCal data from Jan 1, 2011 onwards. Everything I've put in prior to that seems to have disappeared! I can't find anything under preferences that mentions archiving/storage. Can I change the setting so that this info is kept forever? And can I get my previous info back?