The Author Links on my site stopped working. Any idea why?

There have been recent upgrades to JetPack. I have no idea what JetPack has to do with my author links, but when I click on an author link, I get the following error message:

Fatal error: Call to undefined function get_avatar_url() in /home/consci7/public_html/wp-content/plugins/jetpack/functions.opengraph.php on line 104

PLEASE HELP ME. THANKS!