It's Earth Day today: Get your green on

Today's Google Doodle is home to a hummingbird, a puffer fish, a dung beetle and a moon jellyfish. It must be Earth Day!

With hundreds of events planned in cities all over the world, there is no shortage of ways to mark the 44th celebration of eco-friendliness.

This year's theme is something more than half the people on earth can relate to: green cities.

"For the first time in history, more than half of the people on earth live in urban areas," says Alex Standen, spokesman for Earth Day Network. "A lot of these cities are ripe for improvement. We are really emphasizing different parts of city infrastructure and how they can be transformed to be more sustainable and eco-friendly."

There is a conference on green cities in Rwanda, a campaign against poisonous plastic materials in Cameroon, celebrations and workshops in Egypt, tree plantings in China and the launch of a new recycling program in the Bahamas.

Here is a look at what's going on in the United States:

Organizers of Earth Day Texas, which has grown from Earth Day Dallas, are expecting 60,000 people at the outdoor festival Saturday and Sunday. Headline speakers will be actor and environmental activist Ed Begley Jr.; CNN Hero of the Year Chad Pregracke, who is known for his environmental work cleaning rivers; and David Mizejewski, a naturalist with the National Wildlife Federation

Columbus, Ohio, has an annual work day today. Organizers estimate that each Earth Day, participants do about 12,000 hours of community service at more than 150 sites planting trees, working in community gardens and cleaning up neighborhoods.

About 5,000 fourth- and fifth-graders from across Oklahoma are headed to Oklahoma City on Thursday for ScienceFest Oklahoma. They will learn about protecting the environment, conserving natural resources and using alternative fuels and technologies. The students will even see a California sea lion show.

At the 25th Annual St. Louis Earth Day Festival on Sunday, visitors can learn about sustainable products and services, meet area non-profit organizations and snack on local, organic and vegetarian foods.

The Smithsonian's National Zoo wants to highlight the dwindling number of 400 Sumatran tigers left in the wild by launching what it calls an "endangered song."

The song, Sumatran Tiger, was recorded on 400 polycarbonate records designed to decompose gradually. The only way to save the song is to digitize and "breed" the music by sharing it through social media, the zoo says. It's being released to 400 music artists, noted bloggers, wildlife conservationists and other social media influencers.

Apple is jumping in. The tech giant is launching a campaign offering free recycling of all its used products and vowing to begin powering all its stores, offices and data centers with renewable energy to reduce the pollution caused by its devices and online services.