泥盆系及其统和阶界限的研究有较长的历史,可追溯到上个世纪。这些界限引起了对生物(化石)或沉积物(相)成分主要变化的观察。这些变化中有些明显地仅具局部或有限区域的重要性,但大多数变化证明可追踪到全世界,它们是由全球性事件引起的。下面那些与全球性事件相吻合的界限称为自然界限。 Devonian and its study of the Union-level boundaries have a long history, dating back to the last century. These boundaries have led to the observation of major changes in the composition of organisms (fossils) or sediments (facies). Some of these changes obviously have only partial or limited areas of importance, but most of the changes prove traceable to the world and they are caused by global events. The following boundaries that coincide with the global events are called natural boundaries.