What does as scientific theory compare to a scientific law?

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

What processes take place before the mature mrna exits the nucleus?

The eruption of a nearby volcano causes a prairie ecosystem to receive a lot less sunlight. which of these is most likely effect on the ecosystem?