The Earth is constantly changing. Nature and humans have played a part in how the Earth appears today. However, natural forces can change the Earth's appearance dramatically.
Erosion occurs everyday, and plays an important role in changing the Earth's surface. Erosion involves the breaking down of rocks and dirt. We can see the effects of erosion when we look at the Grand Canyon. The Grand Canyon is the result of millions of years of erosion. Many examples can illustrate the importance of erosion. For example, when you go to the beach and look at the billions of grains of sand, you can see how the oceans have eroded the Earth's surface.
Rock formation is also important in shaping the Earth's appearance. Sedimentation is one type of rock formation that determines the texture or shape of a particular landscape.
Plate tectonics is one of the most immediate ways in which we can see how the Earth can change in a small period of time. Earthquakes are a result of plate tectonics, and so are volcanoes and mountains. You can think of the Earth's crust as floating over a rubbery-pliable surface which is the upper mantle. The crust is also divided into plates. So, for instance, the North-American plate is constantly grinding against the Pacific plate. This is why San Francisco and Los Angeles have massive and destructive earthquakes which may result in the movement of California's western coast to move upwards, near Oregon, in the next few billion years.
Volcanism is a consequence of a plate moving over a hot spot or an "open sore" of the crust and mantle. Volcanism is not actually as destructive as it may seem; in fact, everyone knows that the islands of Hawa'ii were formed by the Pacific plate moving over hot spots. Different types of volcanoes have different effects. For instance, if the volcano found in Yellowstone erupts, it will destroy hundreds of kilometers of nature in its path, and the amount of ash and dust it will displace will cover up the Sun and consequently result in an ecological change.
Less commonly found are large asteroids and meteorites. Asteroids will, upon impact, create impact craters and change the Earth's surface, but usually the Earth's atmosphere breaks down any falling material so much so that we rarely realize how many small meteorites actually are able to fall on Earth on a daily basis.
Even if humans are adding to the change in the Earth's appearance, nature's very important role is apparent.