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 smear layer was examined from two aspects; the first âdownontoâ the smear layer and the second from the side or profile view. Photomicrographs obtained by SEM showed that the smear layer consists of two confluent components. A thin superficial layer 1-2 micrometres thick overlying a densely packed layer that penetrated into the dentinal tubules for distances of up to 40 micrometres.