It's not entirely accurate to say the entire Earth's crust changed at once. The Earth's crust is constantly evolving through a process called plate tectonics. Here's a breakdown of how it works:

* Earth's Structure: The Earth has several layers: the crust (outermost), the mantle (thickest layer), the outer core, and the inner core.

* Plate Tectonics: The Earth's crust is broken into large pieces called tectonic plates. These plates "float" on the semi-molten mantle and constantly move, sometimes colliding, separating, or sliding past each other.

* Plate Movement: The movement of these plates is driven by heat and pressure from the Earth's interior. This movement causes:

* Continental Drift: The continents we know today have been moving and changing position for millions of years.

* Mountain Formation: When plates collide, the landmasses can buckle and fold, creating mountain ranges.

* Earthquakes: Sudden shifts along plate boundaries cause earthquakes.

* Volcanoes: When plates separate, magma from the mantle can rise to the surface, creating volcanoes.

So, it's not a singular event that changed the Earth's crust, but a continuous process of movement and interaction between the tectonic plates. This process has been happening for billions of years and continues to shape the Earth's surface as we know it.