The Earth's outer core freezes, if the inner core continues to grow at its current rate of 1 mm per year. Without its liquid outer core, the Earth's magnetic field shuts down, and charged particles emanating from the Sun gradually deplete the atmosphere. Earth's surface temperature, even at the poles, reaches an average of c. 422 K (149 °C; 300 °F). At this point, all life, now reduced to unicellular colonies in isolated, scattered micro-environments such as high-altitude lakes or subsurface caves, will go extinct.