Ren pulled the string tight across the kitchen tiles. “This whole line is Earth’s story,” he said, pointing far down the hall. “Dinosaurs don’t show up until very late.” Then he caught himself and added, more softly, “So we start with the really long, slow part.”

Sam took long steps past paper signs for the first oceans and tiny sea life. Blue chalk waves curled across the floor. “All this happened before dinosaurs?” Sam asked.

“Almost all of it,” Ren said. Mina hopped ahead. “Wow,” she said, “they really missed the beginning.”