Why do scientists break earth's history down into smaller pieces

Why might a placoderm be more useful index fossil than a cockroach?

Scientists once classified a diverse group of eukaryotic species into kingdom Protista. However, in modern evolutionary classification, protists are not grouped together in their own clade, and the concept of kingdom Protista has little meaning.

The water on the Earth today has been sustaining life for millions of years.

An astronaut travels from Earth to the moon. The moon is much smaller than Earth. Which statement describes what happens to the astronaut as he approaches the moon? A. His weight decreases. B. His weight increases. C. His mass decreases. D.

Which energy conversion takes place in plant cells, but never in animal cells? a. chemical energy to the energy of motion b. light energy to chemical energy c. chemical energy to light energy d. the energy of motion to sound energy

An individual who has an eating disorder along with intense thirst and wildly varying body temperatures may have a dysfunction of the medulla. hypothalamus. thalamus. pons. brainstem.

What consists of loose connective tissue that binds the tunica mucosa to the next layer

I tend to have an inquiring mind, and i want to know more about how water moves within the plant body. i take a common houseplant and cut the stem off about 1 inch from the soil surface.

How are mosses and horsetails similar to ferns

Determine approximately how much total energy is lost from a three step food chain if 1000 calories enter at the autotroph level