Reopening cell origins in 1967
Publishing as Lynn Sagan, she proposed a sequence of ancient symbioses in On the Origin of Mitosing Cells in 1967. Acknowledging earlier proposals, the paper combined cytological, biochemical and paleontological material and offered predictions that could be investigated experimentally.
References: [2]
Organelles and different genetic ancestries
This approach connected organelles with formerly independent microorganisms. It required explanations of organelle genetic systems and host relationships, not just structural resemblance. Subsequent research supported bacterial origins for mitochondria and plastids while revising the identity of the host and proposed evolutionary sequences.
Different proposals, different evidential outcomes
The 1967 scheme also connected eukaryotic flagellar structures with spirochaetes. That proposal did not gain supporting evidence and is distinguishable from the widely accepted endosymbiotic origins of mitochondria and plastids. Margulis helped make symbiosis a testable explanation of cell evolution without every part of her initial scheme being confirmed.
References: [3]
Microbial evolution and planetary-biology training
She worked at Boston University and UMass Amherst and participated in NASA-supported microbial-evolution research. In 1980 she established a Planetary Biology Internship program connecting graduate students with NASA and NASA-supported laboratories. She also collaborated with James Lovelock on the Gaia hypothesis and wrote for specialist and public audiences.
References: [1]