Looking for a book from my childhood (was read aloud in 3rd grade, I'm 35) and as the title says, the Earth has been paved over. Further details I recall are that the story follows a girl growing up living in a car train type vehicles and everyone is strapped into motorized wheelchairs. They also only eat food called calorie sticks. They watch robots fight or race on TV for entertainment.
One day, breaking from the normal bland things of life, she notices an apple tree growing up from the pavement. After passing it several times, the travel vehicle stops one day and she gets free of her wheelchair and crawls to the apple tree. Sadly one of the robots immediately finds her and destroys the tree, paving it over. I believe she may have gotten an apple.