Thirty-five years ago—the year before the first Earth Day—many of the major environmental problems of the day seemed so enormous, pervasive, and intractable, that progress must have looked impossible. More than a hundred million highly polluting cars filled the highways. Tens of thousands of industrial and municipal facilities, from city sewer systems to factories, spewed pollution unchecked into air and water. Persistent and frighteningly hazardous pesticides were the norm. And despite these obvious problems—commentors likened breathing the air in Portland to smoking a pack of cigarettes each day—there was precious little political momentum to do anything systemic about them, and most environmental laws hadn’t even been conceived.

But 35 years later, the landscape is completely different. Big-picture trends in pollution are largely going in the right direction. Slower, admittedly, than we’d like. But while many of the most hazardous substances—DDT, PCBs, leaded gasoline—have left a legacy of contamination that still plagues us today, that legacy is gradually dying out.

Such advances didn’t happen overnight, but resulted of a slow accumulation of lots of small changes, both in people’s attitudes and in policies, that have taken decades to take hold. Progress hasn’t necessarily been steady, and some trends have stalled. But 35 years later, the problems that might have seemed completely pie-in-the-sky—say, shifting the entire US auto fleet from leaded to unleaded gasoline—are now old news.

Today’s problems—the rising accumulation of greenhouse gases in the atmosphere, the gradual erosion of biological diversity, the steady loss and degradation of natural habitats, even some newly troubling and persistent toxic chemicals—seem just as huge, abstract, and insurmountable today as did the pollution problems addressed by the first wave of environmental laws.

But if the memory and celebration of Earth Day teaches us anything, it is that even the biggest problems can yield to patience, time, and a steady will.