tertsiaal

Tertsiaal is a term used in various contexts, most notably in music and geology. In music theory, a tertsiaal refers to an interval spanning three diatonic scale degrees, such as a third. This could be a major third, minor third, or augmented third. The concept of thirds is fundamental to understanding harmony and chord construction in Western music. For example, a triad is typically built by stacking two thirds on top of each other.

In geology, the term tertsiaal describes a specific geological period, also known as the Tertiary Period. This period began approximately 66 million years ago, following the Cretaceous-Paleogene extinction event, and ended about 2.6 million years ago with the start of the Quaternary Period. The Tertsiaal is characterized by the diversification and dominance of mammals, the evolution of birds, and significant changes in flora. Major geological events during this time included the formation of mountain ranges like the Himalayas and the Alps, and fluctuations in global sea levels and climate. Paleontologists study fossils from the Tertsiaal to understand the evolution of life and Earth's history. The term "Tertiary" is sometimes replaced by "Paleogene" and "Neogene" in modern geological nomenclature, which together encompass the traditional Tertsiaal period.