Theories may change over time. In ancient times, people observed that living things seemed to arise from nonliving things. They observed that maggots would
often appear on rotting meat. This became known as the Theory of Spontaneous
Generation and was widely accepted for many years. In 1668, Anton van
Leeuweenk invented the microscopes which allowed him to see microorganisms
for the first time. Upon observing the rotting meat under magnification, scientists
changed their understanding of living things.
What theory did this new information lead to?