When did the first plants on earth begin to grow on land and what were they called? July 18, 2014 by Karen Hill | Filed Under: Earth The first plants to begin growing on land were bacteria, or microscopic plants, in the Ordovician period, 505 to 438 million years ago. Lichens, mosses, and liverworts followed the bacteria onto land. Before the Ordovician period ended, a varied plant population, including ferns and trees, extended all over Earthâs land masses. Related
The iris (plural: irides or irises) is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. Eye color is the color of the iris, which can be green, blue, or brown.
The eye is a slightly asymmetrical globe, about an inch in diameter. Just behind the iris and pupil lies the lens, which helps to focus light on the back of the eye. Most of the eye is filled with a clear gel called the vitreous. Light projects through the pupil and the lens to the back of the eye. The inside lining of the eye is covered by special light-sensing cells that are collectively called the retina. The retina converts light into electrical impulses. Behind the eye, the optic nerve carries these impulses to the brain. The macula is a small extra-sensitive area within the retina that gives central vision. It is located in the center of the retina and contains the fovea, a small depression or pit at the center of the macula that gives the clearest vision. Eye color is created by the amount and type of pigment in the iris.