There are many Earth Day activities scheduled for this weekend that you can participate in. In Broadview there are several volunteer events at Carkeek Park. The Carkeek Watershed Community Action Project is sponsoring an annual event for all ages. Here is a link to to more information. http://act.earthday.org/event/carkeek-park-earth-day-32nd-annual
Also at Carkeek Park is the monthly Carkeek STARS volunteer work party. Volunteers do forest restoration and trail maintenance work. http://www.broadviewseattle.org/carkeek-stars-jan-15-2011/
There are parks volunteer events all around the city. See the Seattle Parks and Recreation volunteer calendar for a list of events you can participate in. http://www.cityofseattle.net/parks/calendar/volunteer.htm#
The weather forecast for Saturday is favorable for doing something outdoors. Enjoy the day!