<span>The geologic time scale is divided into periods, which are then divided into epochs, which are further divided into ages. For example, the time of the dinosaurs lasted 3 periods (Triassic, Jurassic, Cretaceous), each period had 3 epochs (late, early, middle), and each age fit into one of those. Many epochs have more than 1 age associated with them.
As for the basis for differentiating the eras, I'm not so sure. The only one I can say for sure is the end of the Cretaceous, which is when the dinosaurs suddenly became extinct due to a meteor impact. I think the divisions are based on significant, global-scale events that changed the world.
Sorry its so long but that the answer i think >:) ur welcome
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Answer:

Plasmodesmata play roles in both cellular communication and in molecule translocation. Plant cells must work together as part of a multicellular organism (the plant); in other words, the individual cells must work to benefit the common good. Therefore, communication between cells is crucial for plant survival.
Answer: Unusual sounds or noises, sights,smells or odors, appearances or behaviors are often
the first sign of an emergency.
Bystander roles in an emergency may include giving first aid, calling 9-1-1 or the designated emergency number, or getting equipment
( for example: A first aid kit).
Explanation:
Stars Like the Sun. When the core runs out of hydrogen fuel, it will contract under the weight of gravity. ... The upper layers will expand and eject material that will collect around the dying star to form a planetary nebula. Finally, the core will cool into a white dwarf and then eventually into a black dwarf.