Robert M. Hazen: Of all the periodic table’s richly varied denizens, carbon, the sixth element, is unique in its impact on our lives. Carbon is not simply the static element of “stuff.” Carbon provides the most critical chemical link across the vastness of space and time — the key to understanding cosmic evolution. Over the course of almost 14 billion years, the universe has evolved, complexified, and become ever more richly patterned with seemingly endless fascinating and quirky behaviors. Carbon lies at the heart of this evolution — choreographing the emergence of planets, life, and us. And, more than any other ingredient, carbon has facilitated the rapid emergence of new technologies, from steam engines of the industrial revolution to our modern “plastic age,” even as it accelerates unprecedented changes in environment and climate on a planetary scale. So here are a few musings about carbon — the most important element in the cosmos.