Happy Earth Day everyone!
As expected, most of the search engines have special logos for the day. Google and Yahoo's logos are animated, Google has a JPG that rotates between images (like an animated GIF but not) to show the evolution of the growth. Yahoo has a nice animated logo, Bing and Ask.com have really nice background themes and even Sogou has a special logo.
Google's logo in stages (warning, a lot of scrolling needed) but before, here is a video of it in action:
This logo was actual photos shot by a Google Doodler over time. Google's Marissa Mayer explained on Twitter:
For Earth Day, doodler Jen actually planted and grew our logo, then made a time-lapse video: google.com— marissamayer (@marissamayer) April 22, 2012
Yahoo's animated logo:
Forum discussion at Google Web Search Help.