People of all ages around the globe are participating in "Acts of Green" this week and next weekend to mark Earth Day, a 42nd annual environmental awareness event. This year's theme -- Mobilize the Earth -- is put into action with tree plantings, cleanups, recycling drives and donation collections by students, community groups, companies, nonprofit organizations and individuals, as described in the Earth Day Network video below.

There also will be fairs, festivals, concerts, fund-raising walks and lots more. The highest-profile event will be a seven-hour National Mall rally in Washington, D.C., on Sunday featuring speeches, renewable energy demonstrations, voter signups, entertainment, information booths and celebrity appearances. The idea there and elsewhere is to increase appreciation of the natural environment and to spread knowledge about threats to it. The United Nations three years ago designated April 22 as International Mother Earth Day, now observed in about 175 countries.

Earth Day began in 1970 with college campus "teach-ins" (mass discussions) focusing on air, water and land pollution. The movement helped raise concern about littering, pesticides, herbicides, wasteful packaging, emissions and other risks to the earth and everything or everyone living on it. Changes in government policies and how we live have brought improvements such as the Endangered Species Act, Clean Water Act, Clean Air Act and many other groundbreaking actions. Still, climate changes and other issues keep the environmental protection crusade continuing.

Official site says: "Together we will stand united for a sustainable future and call upon individuals, organizations, and governments to do their part." -- www.earthday.org/2012

Critics say: Earth Day has become an empty ritual with more celebrating than productive action, some environmentalists feel. People with different views say it's too political, anti-business and critical of development.

Blogger writes: "Earth Day reminds us we all share the same planet. . . . It reminds us that protecting Earth is every person's and every country's responsibility." -- Michelle Wolfson, parent in Gloucester Township, NJ, blogging at patch.com