All of you have experienced the pleasures of the outdoors; a picnic in the park or a hike in the wilderness. While in a park or a forest, have you ever wondered what composes the landscape? That is, have you ever dissected the scene into smaller and smaller parts?

Let's do this to a scene along the Ken Patrick Trail, a densely wooded rim trail of the Earth's watermark, the Grand Canyon.

As shown here, a plant leaf is made up of a gridwork of cells. If you could peer into the structure of animals and microbes, you would find that they too are composed of cells. All living organisms that we can see with our eyes are made of cells. Most cells are very small; about a millionth of a pencil lead in width. Some cells are large, like the yellow yoke of an egg.

Knowing now that life is made up of cells, how was this fact discovered? Who were the first people to see cells, and recognize their role as building blocks of larger organisms? A brief historical perspective is in order.