These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing.
As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
The mathematics of inferring backwards from measurements to age is not appropriate for most students.
This is the second lesson in a three-lesson series about isotopes, radioactive decay, and the nucleus.
Terry Harrison of New York University, leading to the recovery of more than a dozen new hominin finds, Dated to 3.7 million years ago, they were the oldest known evidence of hominin bipedalism at that time.
Subsequently, older Ardipithecus ramidus fossils were found with features that suggest bipedalism.
A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved.
However, by itself a fossil has little meaning unless it is placed within some context.