When, and how often, has multicellular life evolved on Earth?

When, and how often, has multicellular life evolved on Earth? The objective of your essay is to describe and critically evaluate the current state of your selected topic. Your paper should do the following: (i) review the recent scientific literature on the topic; (ii) present a balanced evaluation of the evidence supporting different viewpoints; (iii) indicate problems or questions that are still unresolved. In evaluating the literature, you may evaluate or comment on any relevant aspect, but you must justify all statements. Include a Literature Cited section (not included in the word count) at the end of your assignment.