 The variation of sea level over time has been reconstructed using oxygen isotope analysis of deep sea cores, the dating of marine terraces, and high resolution oxygen isotope sampling from ocean basins and modern ice caps.A drop of eustatic sea level by about lower than present-day levels, commencing around 30,000 years BP, created Beringia, a durable and extensive geographic feature connecting Siberia with Alaska.With the rise of sea level after the Last Glacial Maximum (LGM), the Beringian land bridge was again submerged.