Molecular biology is a field of biology that looks at the molecular machinery of life. The field was founded in the early 1930s, though the phrase was only used in 1938 and the field didn't take off until the late 50s and early 60s. Since then, progress in the field has been massive.
The Ionosphere and the Exosphere (minor layers) are parts of the Thermosphere (major layer). The ionosphere is part of the theremosphere.
There are three sub-layers within the epidermis itself: the outer stratum corneum, the middle squamous cell layer, and the bottom basal cell layer. The stratum corneum is the visible part of the epidermis and is actually a layer of dead skin cells immediately on the skin's surface. This layer uses a protein called keratin to form a tough barrier between the outside world and the more vulnerable cells inside the skin and body.