Puffy Nation

Latching onto a meteor shower, hundreds of Churns rain down into the earth's oceans and slowly burrow into the sand only to erupt on land a decade later. The Churns are living nano replicators that have wiped out the human race except for a few people on ocean liners and oil rigs. 

Humans blame the nanobots that escaped Tun Technology white rooms but Churns are not man made. They are alien technology.

Each Churn has a 'seed' that determines its pattern and it grinds up the earth and recreates this pattern over and over. The Churn's obsession can be a fractal, based on human architecture, or something as random as a dog's head. Throwing thin ropes across water, the Churn spreads from continent to continent, covering territories so vast they begin to merge into a super continent. The only place safe from them (for now) is the deep ocean.