The Appalachian Mountains are among the oldest mountain ranges on Earth, with a complex geological history spanning over a billion years.

• The initial geological processes that led to the formation of the Appalachians began about 1.1 to 1.2 billion years ago during the Precambrian era, involving sedimentation, volcanic activity, and metamorphism of rocks

• The first significant mountain-building event related to the Appalachians, known as the Grenville orogeny, started around 1.25 billion years ago and lasted about 270 million years

• Subsequent major mountain-building episodes occurred during the Paleozoic era, including the Taconic orogeny (~450 million years ago), the Acadian orogeny (~375 million years ago), and the Alleghanian orogeny (~325 million years ago), which contributed to the formation of the supercontinent Pangea and the uplift of the Appalachians near its center

• The mountains as we see them today were mainly formed approximately 260 million years ago during the late stages of these orogenies, although erosion had reduced them to near flat plains by the end of the Mesozoic era (~66 million years ago)

• The current topography of the Appalachians was rejuvenated by uplift during the Cenozoic era (starting about 66 million years ago), which caused streams to cut into the ancient bedrock and shape the present landscape

In summary, the Appalachians are roughly 480 million years old in terms of their initial mountain-building, but their geological roots extend back over a billion years, making them one of the oldest mountain ranges on Earth