Process art is art that explores the act of producing art, and is often less concerned with the object or work that is eventually produced. The process art movement began in the 1960s and can be seen in the paintings of abstract expressionist Jackson Pollock, which were at least in part defined by the process through which he made them—the drip and splatter process. Other art movements also have overlaps with process art, including earthworks (land art), because of the way in which the environment acts upon them after they are created. The often monumental yet minimalist work of American sculptor Richard Serra (1939–) is a good example of process art. His steel sculptures encourage viewers to think about the nature of the materials and the way in which they were put together. What at first seems simple—a tall, tower-like slab of steel, for example, becomes a curiosity as one contemplates “how.”