Share This button not displaying

Found at http://www.Earthascope.com

I can’t figure out for the life of me why my Share This button will not display. I have the plugin file in the correct place and the code in my singlepost.php

See here for what my code looks like:

<?php get_header(); ?>
<?php if (have_posts()) : ?>

		<?php while (have_posts()) : the_post(); ?>
<div class="excerpt" id="post-<?php the_ID(); ?>">
								<div class="excerpt_header snap_nopreview"><a href="<?php the_permalink() ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a></div>
								<div class="excerpt_subheader snap_nopreview">
									<div class="excerpt_subheader_right"></div>									<div class="excerpt_subheader_left">
										By
										<?php the_author() ?>
																													</div>
								</div>
								<a href="http://www.stumbleupon.com/submit?url=<?php the_permalink(); ?>&title=<?php the_title(); ?>"><img src="http://cdn.stumble-upon.com/images/16x16_su_3d.gif" align="absmiddle"> Stumble It </a>:: <?php if (function_exists('sharethis_button')) { sharethis_button(); } ?>:: <a href="http://www.feedburner.com/fb/a/emailverifySubmit?feedId=1903223&amp;loc=en_US"><img src="http://www.envirohumanimpact.com/wp-content/themes/mimbo2.2/images/emailmini.jpg" align="absmiddle"> Subscribe via Email</a> :: <a href="http://www.envirohumanimpact.com/feed"><img src="http://www.envirohumanimpact.com/wp-content/themes/mimbo2.2/images/rssmini.jpg" align="absmiddle"> Subscribe via RSS</a><div class="entry">									<?php the_content('<p class="serif">Read More &raquo;
'); ?>

</div>
							</div>
								<?php endwhile; ?>		<?php comments_template(); ?>  

							</div>
							 <?php else : ?>

							      <h2 class="center">Not Found</h2>
      <p class="center">Sorry, but you are looking for something that isn't here.

	<?php endif; ?>		

<?php get_sidebar(); ?>

</div>
<?php get_footer(); ?>

Anyone have any ideas?

Thanks in advance!