The only constant in the world of SEO is changing. In fact, Google is reported to change its search algorithm around 500 to 600 times each year.

While most of these updates are small and often aren’t even picked up by users and SEO, every once in a while, Google releases major updates.

Below are links to some of the most important resources for search marketers:

January 8, 2016: Unnamed Update

Multiple tracking tools (including MozCast) reported historically-large rankings movement, which Google later confirmed as a “core algorithm update”. Google officially said that this was not a Penguin update, but details remain sketchy.

February 23, 2016: AdWords Shake-up

Google made major changes to AdWords, removing right-column ads entirely and rolling out 4-ad top blocks on many commercial searches. While this was a paid search update, it had significant implications for CTR for both paid and organic results, especially on competitive keywords.

May 10, 2016: Unnamed Major Update

MozCast and other Google weather trackers showed a historically rare week-long pattern of algorithm activity, including a 97-degree spike. Google would not confirm this update, and no explanation is currently available.

May 12, 2016: Mobile-friendly 2

Just more than a year after the original “mobile friendly” update, Google rolled out another ranking signal boost to benefit mobile-friendly sites on mobile search. Since the majority of sites we track are already mobile-friendly, it’s likely the impact of the latest update was small.

September 1, 2016: Possum

While unconfirmed by Google, MozCast recorded extreme temperatures of 108° and a drop in local pack prevalence, and the local SEO community noted a major shake-up in pack results. Data suggests this update (or a simultaneous update) also heavily impacted organic results.

September 13, 2016: Image/Universal Drop

MozCast recorded a nearly-record 111° temperature and a 50% drop in SERPs with image (universal/vertical) results. The universal result shake-up opened up an organic position on page 1, causing substantial ranking shifts, but it’s likely that this was part of a much larger update.

September 23, 2016: Penguin 4.0 Announcement

After almost two years of waiting, Google finally announced a major Penguin update. They suggested the new Penguin is now real-time and baked into the “core” algorithm.

Initial impact assessments were small, but it was later revealed that the Penguin 4.0 rollout was unusually long and multi-phase (see September 27th and October 6th).

September 27, 2016: Penguin 4.0, Phase 1

The first phase of Penguin 4.0, which probably launched around September 22-23, was the rollout of the new, “gentler” Penguin algorithm, which devalues bad links instead of penalizing sites.

The exact timeline is unconfirmed, but we believe this rollout took at least a few days to fully update and may have corresponded to an algorithm temperature spike (113°) on September 27th.

October 6, 2016: Penguin 4.0, Phase 2

The second phase of Penguin 4.0 was the reversal of all previous Penguin penalties. This seemed to happen after the new code rolled out, and may have taken as long as two weeks.

Post-Penguin activity had one final peak on October 6th (116°), but it is unclear whether this was Penguin or a new update. Algorithm temperatures finally started to drop after October 6th.

November 10, 2016: Unnamed Major Update

MozCast detected a major (106°) spike on November 10th and another on the 18th. Industry chatter was high during both periods, with some suggesting that the second spike was a reversal of the first update.

Google has not confirmed either event. Many people reported bad dates in SERPs during the same time period, but it’s unclear whether this was causal or just a coincidence.

Reference blog from Moz.com