In 1991 David Sparks and Mark Parmentier, both then at Brown University, proposed an answer rooted in the variable temperature of ocean crust and the uppermost mantle.

• 1991年，美国布朗大学的斯巴克斯（DavidSparks）与巴曼提耶（MarkParmentier）提出解答，关键就在海洋地壳与地函顶层的温度变化。