Complex sentence: By the mid- 1990s, Hazen felt that his research had reached a "respectable plateau" where the main principles of how crystals compress were known, so the questions he was asking were increasingly narrow and the answers rarely surprising.
Split into simpler sentences: By the mid- 1990s, Hazen felt that his research had reached a "respectable plateau" where the main principles of how crystals compress were known. The questions he was asking were increasingly narrow and the answers rarely surprising.