It was only explored in a gross sense. As a measure of this, it's estimated that we only know of between 2/5ths and 1/15th of all species (http://www.enviroliteracy.org/article.php/58.html). The oceans, which comprise 95-99% of the living space on the planet by volume (Bill Bryson, A Short History of Nearly Everything), are almost completely unknown. There are still places to go to get away from things.
In the 80s, I'm pretty sure the planet was mostly explored.