The EPA was founded on December 2, 1970. Unleaded auto gas (then called "white gas") had been on the market for some time but most people didn't buy it except for things like Coleman stoves and lanterns.

The switch to unleaded gas for cars really began with the introduction of catalytic converters in cars in 1975. Lead destroys a catalytic converter. Within a few years, you couldn't buy leaded gasoline anywhere in the US except at airports. Most piston engined airplanes still used leaded gas (100 octane low lead), although those of us with lower compression engines run premium unleaded auto gas in our planes. We sometimes will buy a few gallons of normal avgas because our valves were designed for leaded fuel.

Odds are even that is likely to change in a few years. The FAA has approved 92 octane unleaded avgas. The question I'd like to know is if it'll work in the planes that require 100 LL. Virtually all piston engined planes built in the last 20 years or so require 100 LL.