Mobile is the name of the game for marketers right now.

The number of mobile-only Internet users surpassed the number of desktop-only Internet users in the United States for the first time ever, according to a comScore study. Moreover, in 10 countries, including the US and Japan, more searches are taking place on mobile devices than on desktops, states Google. And mobile digital media time is consistently outpacing time on desktop and other media, according to the latest Kleiner Perkins Caulfield & Byers mobile technology trends report.

What Google Changed

Search engines on desktops and mobiles used to deliver largely identical results, regardless of whether the searcher used a desktop machine or a mobile device. However, early this year, Google announced it would be implementing a new algorithm update that would add mobile-friendliness as a ranking signal.

April 21, 2015 was the official inception date, and Google detailed that the update would affect SERPs on mobile devices, demoting sites that were not mobile-friendly while presumably promoting those that were.

Though Google was the first search provider to begin tailoring results to different devices, other major search engines began to follow suit. Not long after Google's update, Bing announced that it would also be rolling out a mobile-friendly ranking algorithm in the following months.

So, with these trends in mind, here are five important things to know about the divergence of mobile search results from desktop search results.

1. The mobile-friendly update is a faucet, not a flood

In the immediate aftermath of the April 21 algorithm update—termed "mobilegeddon" by many in the SEO community—people began voicing their skepticism about the effects of the change.

Extreme shifts in mobile SERPs weren't seen, and many people who were underwhelmed felt that Google had exaggerated the update. But this update was never intended to be the one and only update as far as mobile search is concerned.

Rather than viewing the mobile-friendly update as an abrupt flood (or, for that matter, an apocalyptic event), think of it as a faucet, which can be turned on gradually as needed. On April 21, Google opened up the tap but only just slightly.

In the months following the update, the faucet's flow has gradually increased. Now, the industry is seeing significantly more discrepancies between mobile SERPs and desktop SERPs. Google will continue to increase the water pressure of this mobile-friendly update as time goes on, and we will continue seeing mobile rankings deviating from desktop rankings as a result.

2. Eventually, Google's algorithm will likely operate on a mobile-friendly spectrum

Google's mobile-friendly test analyzes a URL and report whether the specified page is mobile-friendly (according to Google's standards).

The test returns binary results—either a page is mobile-friendly or it is not; there is no middle ground. However, as mobile continues to grow and as more websites adopt a mobile-first mentality, Google will likely re-evaluate its test to function on a spectrum. There will be degrees of mobile-friendliness, taking into consideration factors such as page-loading speeds, usability, viewport configurations, and more.

For example, a site with a responsive design but excessively long load speeds may face lower rankings than an m-dot site without click-to-call functionality built-in or vice versa. Both hypothetical sites have mobile-friendly elements. However, they both also have mobile-unfriendly elements that could negatively impact user experience and satisfaction.

3. The update you didn't hear about: app inclusion in search

A second, quieter announcement in the days following the mobile-friendly update detailed that Google would begin returning app listings in search results on mobile devices.

In the past, apps have been included in mobile SERPs but only those that were already installed on the user's device.

This update is indicative of another potential trend: Google may begin prioritizing apps in search results. Apps are very singular, typically geared towards a very specific purpose or target audience. Therefore, app search results relevant to certain key phrases could prove useful. Though still in the initial stages, it's definitely something to keep an eye on in the upcoming months.

4. Geolocation will play a huge role in mobile search results

Have you ever asked Siri to find the closest Italian restaurant to you or done a search on your phone for an urgent care center? Chances are your mobile returned results based on your location—perhaps a list of the six Italian restaurants within a five-mile radius of your car's location or the closest urgent care center currently open.

At a desktop, Google has a vague idea of your location based on your ISP, usually down to the ZIP code. With mobile devices (so long as location services are enabled), however, Google uses a combination of WiFi, 2G/3G/4G, and GPS satellites to more precisely locate the searcher's location. Thus, mobile search results are becoming more and more granular, based upon user location.

Also, as geolocation-based results continue to flourish, they will edge out other results served in the SERPs.

5. Usability is a major factor, and it will only become more important over time

Google's primary goal with its search engine has always been to provide value for its searchers by consistently returning the best results and the best user experiences. That's why, in the past, algorithm updates have targeted sites with poor content and spammy links.

With this update in particular, one of the biggest factors affecting a site's mobile-friendly ranking is usability. For example, mobile screens are significantly smaller than desktop screens, and font sizes that are too small and sites requiring zooming and horizontal scrolling will likely annoy users.

Likewise, tap targets are not appropriately sized (i.e., too small for the average finger pad to comfortably press) can contribute to user frustration as well. Frustrated users are more likely to bounce a site and, thus, bounce rate is likely to become a predicting factor for mobile site rankings as well.

Other factors Google might use to evaluate usability include time-on-site, pages viewed, and on-site user behavior.

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Google's primary interest, in its own words, is "to deliver the most relevant—and useful—information to people seeking answers." Regardless of searchers' device of choice, the search giant aims to "to ensure a meaningful 'after-click' experience that helps people use information relevant to their task."

So, if your website doesn't render well on mobile, it only makes sense that it wouldn't rank well on mobile. That's what Google's addition of mobile-friendliness as a ranking signal is designed to do. It's not hard to imagine a future in which the mobile version of the Google SERPs is almost completely different from the desktop version. That's why, if your website isn't currently mobile-friendly, now is the time to take preemptive action and adapt your site to the new mobile-first environment.