Question

the first organisms on earth appeared approximately 3.8 billion years ago and were all unicellular. multicellular organisms have only existed for about one billion years.
what evolutionary milestone made it possible for more complex multicellular organisms to exist?
a. appearance of stem cells
b. appearance of eukaryotic cells
c. appearance of prokaryotic cells
d. appearance of photosynthetic cells

Explanation:

Eukaryotic cells have a nucleus and membrane - bound organelles, which allowed for greater cellular complexity and the development of multicellular organisms. Prokaryotic cells are simpler and unicellular. Photosynthetic cells are related to energy - production and stem cells are related to cell differentiation in already complex organisms.

Answer:

B. appearance of eukaryotic cells