Totally boggles my mind. But hey, like any scientist I simply analyzed the empirical data provided and made an educated hypothesis.
Came on the scene in 1872. It literally had a 100-year head start over Earth Day, which premiered in 1970. AD also has a simple premise. Encouraging folks to plant trees. And lastly, Arbor Day has a primo time slot – the last week in April. One week before Iron-Man 2 comes out.
Began as a movement started by Wisconsin senator Gaylord Nelson. His orignal idea was to simply educate people on conservation issues. The first holiday had 20 million people (mostly college kids) across the U.S. preaching about environmentalism and getting high. Of course now ED has billions of people involved. And it even has an entire week. Country leaders make speeches. There are Earth Day conferences planned at really nice hotels. Parades. Fairs. And U2 caps off the week with a huge all out musical extravaganza.
EARTH DAY. No contest!!!
Arbor Day suffers from being too niche a holiday, Tree Hugging. E-day covers the entire GREEN spectrum. PLUS, Earth Day also does a better job in the marketing department and is endorsed by BONO.