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.
The periosteum consists of an inner osteogenic layer and an outer fibrous layer. Periosteum consists of dense irregular connective tissue. Periosteum is divided into an outer fibrous layer and inner cambium layer (or osteogenic layer). The fibrous layer contains fibroblasts, while the cambium layer contains progenitor cells that develop into osteoblasts.