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.
Definition of Minor Arc. Minor Arc is smaller of the two arcs formed when a circle is divided into two unequal parts. 1  The measure of the minor arc is always less than 180Â° or Ï radian.  The sum of the measures of the major arc and the minor arc is equal to 360Â° or 2Ï radian.