Great Falls Tribune: In its almost four decades, Earth Day – today – has become a catalyst for cleaning up the environment and, in a world inhabited by more than 6.6 billion people, living more responsibly. In modern parlance, the term is "reducing your environmental footprint" – and more specifically of late, reducing your "carbon footprint." What that means is living in a way that leaves less of a mark on the world, whether through the modern Three Rs of reducing, reusing and …