Simplify the following text for a Grade 10 native English-speaking person.
Original: More recent variants in the 1980s and 1990s include GÃ 1\/4 nter WÃ chtershÃ user 's iron-sulfur world theory and models introduced by Christian de Duve based on the chemistry of thioesters .
Simplified: In the 1980s and 1990s , GÃ 1\/4 nter WÃ chtershÃ user came up with the iron-sulfur world theory and Christian de Duve introduced models based on the chemistry of thioesters .