Complex sentence: In an attempt to colonize Mars, 21st century scientists tasked with terraforming the planet seed it with a modified algae to absorb sunlight and purify the atmosphere, and cockroaches whose corpses spread the algae across the planet as they feed.
Split into simpler sentences: In an attempt to colonize Mars, 21st century scientists are tasked with terraforming the planet. Their goal is to seed the planet with a modified algae to absorb sunlight and purify the atmosphere, and cockroaches, whose corpses spread the algae across the planet as they feed.