The Holocene epoch marks a profound shift in Earth's climate history. It begins precisely 11,600 years ago at the end of the Younger Dryas, a boundary that separates the Pleistocene from the modern geological era. This transition brought sea levels substantially higher than present and initiated the climatic conditions that have defined human civilization. The correlation between this warming period and rising sea levels has long been recognized, but the precision of that 11,600-year marker reflects decades of refinement in ice core data and geological evidence. Understanding this boundary is essential because it represents the baseline against which all modern climate discussions must be measured.