What are the benefits of having stem cells?

Which of the following occurs after a natural or unnatural disturbance in an ecosystem

What did not occur in the proterozoic eon a)the oxygen levels increase greatly in the atmosphere,b)the emergence of the eukarya , c)muti cella’s eukaryotic organisms began to diversify,d)anaerobic bacteria kept thriving with more oxygen

Fredrick griffith made a scientific discovery in 1928