how can scientist use the microscope to know wheter something is alive?

Answer 1

They can't. Just by looking at something won't tell you if it's alive. I always look at lichens and I am continually amazed that they are alive at all, but they are. And trust me, the smaller something is the less it looks alive for the most part. But there are some cases that a microscope will show you something is alive. Small Protists, like Paramecia, have contractile vacuoles that look like a blinking eye under a microscope, and motile microbes like E. coli, Amoebas, and Cholera bacteria have very recognizable moving patterns that can't not be mistaken as random movement. Otherwise, life is very slow under a microscope.

Answer 2

they don't they use special robots to take samples of soil from uther plantes the also test the ice for life on other planets