Plant trees, the most popular activity performed to celebrate the Earth Day. As the date also roughly coincides with U.S. Arbor Day, over time Earth Day has taken on the role of tree-planting. Planting trees helps to reduce greenhouse gas emissions, cleans pollution, secures soil in place to prevent erosion, and provides homes for a lot of biodiversity.
Earth Day is a good time to make a commitment to learning more about the environment and how you can help to protect it. Borrow some library books and read up on an issue such as pollution, endangered species, water shortages, recycling, and climate change. Or, learn about a region you've never considered before, like the Arctic, the deserts, or the rainforests. Think about the issues that concern you the most and if you haven't done so already, join a local group that undertakes activities to help protect the environment in your area.