How is the Earth’s crust changing and how do we know?

The earth’s crust is constantly changing due to a process called plate tectonic. The other natural changes include changes incurred by rivers etc.
We know because we can see it in:
Earth crust is constantly changing primarily due to plate tectonics (plate motion) but it also changes from activity on the surface from river man made and meteorite impact.
Earth’s crust is constantly changing and plate material is always being created and destroyed. Continents and oceans do not ride atop the plates without changing. As the plates move and change so do the continents and oceans.
mountains that circle Earth are called the Global Mid-ocean Ridge. Magma is pushing up from Earth’s interior all along this ridge and creating new crust. The same forces that pull the plates apart also allow magma from Earth’s interior to come up along the ridges and create new crust. Areas where new crust is created and plates are forced apart are called spreading centers.
Although the movement of the plates away from spreading centers is very very slow (about one inch per year) it has been happening for millions of years. Thus very small changes have become very large over time.
A great example of a change caused by a river is the Grand Canyon in the US. Humans may change the crust by altering flows of rivers mining etc.
But it is important to note that big changes that create entire islands or a mountain ranges to form are the result of plate tectonic.