essential

Maybe not today, because we have better ways to fight disease, but knowing what was out there is essential.

"Hydrothermal systems were essential for the development of life on Earth and our findings suggest Mars also had water, a key ingredient for habitable environments, during the earliest history of crust formation."

Well, it's not essential if church is not an essential part of your life.

There are many things to be said here, about essential humanity united in the basic functions.

Liu, who lives in Manhattan, elaborated on why her library card, spur-of-the-moment theatergoing and riding her bicycle are essential to her well-being.