How does Google AMP affect my SEO and organic rank?

Let’s put it this way: If you are not using Google AMP as a publisher, you will see declines in your mobile organic search traffic if( you have not already seen that decline). If mobile traffic within the organic search channel is important to you, then AMP really matters.

It is critical to understand the actual mechanism for AMP pages to appear in the AMP index (only visible in Webmaster Tools).  Your Google AMP pages will ONLY be indexed based on the following:

• The MOBILE page is requested in a search result (more on this below)
• The AMP meta data is present
• The pages are valid AMP pages

The existence of AMP pages do not affect the actual position in the SERP. However, the carousel (AMP rich-result) appears first in the result and is the most prominent. If you are not participating in AMP, you will miss out on that traffic.  Only AMP pages with valid structured data are eligible for the AMP carousel.

The content on the AMP pages should be as close as possible to the mobile page.  If it is significantly different Google will ignore the AMP page and it will appear as an error in Webmaster Tools.  The content on the AMP pages does NOT affect the actual postion in the SERP.  Google ONLY uses the mobile version of the page to determine that.  This is why the AMP page needs to be as close as possible to the mobile page.

While Google AMP is not specifically a ranking factor, it does represent a more streamlined user experience.  If you have done a good job with your implementation, the visitor experience will be even better than mobile.  That makes for additional engagement and sharing.  Those are two major off-page factors that ultimately impact search performance.