the outer part of the earth's atmosphere. It begins at an
altitude of about twenty-five miles. It is made up of layers of gases that have been ionized (changed into groups of
atoms that have
electrical charge).
the outer part of the Earth's atmosphere, beginning at an
altitude of about 25 miles and extending to the highest parts of the atmosphere.
the outer part of the earth's atmosphere which begins at an
altitude of about twenty-five miles. It is made up of layers of gases that have been ionized (changed into groups of
atoms that have
electrical charge).