Today, most people are searching on Google using a mobile device. However, their ranking systems still typically look at the desktop version of a page’s content to evaluate its relevance to the user. This can cause issues with content ranking and relevance when the mobile page has less content than the desktop page. Google’s search algorithms are not evaluating the actual page that is seen by a mobile searcher.
Although Google’s search index will continue to be a single index of websites, their algorithms will eventually primarily use the mobile version of a site’s content to rank pages from that site, to understand structured data, and to show snippets from those pages in their results. Of course, while their index will be built from mobile documents, Google’s focus is to continue to build a great search experience for all users, whether they come from mobile or desktop devices.