What is the earliest form of writing, characterized by wedge-shaped marks on clay tablets?

The earliest form of writing characterized by wedge-shaped marks on clay tablets is known as cuneiform. This writing system emerged in ancient Mesopotamia around 3200 BCE and is considered one of the first forms of written expression. Cuneiform was developed by the Sumerians and was initially used for record-keeping and administrative purposes, such as documenting transactions, laws, and trade. The distinctive wedge shapes were created by pressing a reed stylus into soft clay, allowing for a stylized yet flexible means of communication.

In contrast, hieroglyphics is a system of writing used in ancient Egypt that combines logographic and alphabetic elements, primarily known for its pictorial symbols. The Phoenician Alphabet is a significant development in writing that came much later, around 1200 BCE, and greatly influenced subsequent alphabets but does not feature the wedge-shaped form characteristic of cuneiform. Runes are associated with Germanic languages and were used several centuries after cuneiform, primarily in Northern Europe, and lack the historical context associated with the early written records of Mesopotamia. Thus, cuneiform stands out as the correct answer to this question due to its historical significance and unique features.