In 2008, a study by Soares "et al.", which included Oppenheimer, examined mtDNA lineages in ISEA and Taiwan and discovered that, at most, only around 20% of modern mtDNA were introduced during the Neolithic. They examined mtDNA Haplogroup E in particular, which they concluded likely evolved from Haplogroup M (specifically Haplogroup M9), that arrived in ISEA more than 50,000 years ago. Although the sea-level rise was mostly gradual starting from ~19,000 years ago in the last glacial period, other studies have shown that there were likely three episodes of catastrophic rise events at approximately ~14,500, ~11,500, and ~7,500 years ago caused by ice sheet collapse. They concluded that these sudden sea level floodings triggered mass population displacements from ISEA and were the initial conditions that triggered the development of the maritime technologies that later defined Austronesian culture.