Mod - Failed validation!

Unsurprisingly, my volcano web page failed its W3C validation test. But what does surprise me is the errors. I don't really understand what is wrong, as the most common point is that the mark up text 'is not closed' see sample paste from validation test. But the tags are closed ... I think these errors are related to useability - as the volc page displays OK. Mmmmmmmmmmm ... 17 errors in one short web page. Eeeek.

1. Error Line 38 column 42: end tag for "I" omitted, but its declaration does not permit this.

        the Earth, over four billion> 

   • You forgot to close a tag, or
   • you used something inside this tag that was not allowed, and the validator is complaining that the tag should be closed before such content can be allowed.

   The next message, "start tag was here" points to the particular instance of the tag in question); the positional indicator points to where the validator expected you to close the tag.