The origin of Earth’s moon, the largest moon in the
(36) system, is still something of a mystery. There are some
theories about its origin however. Now, keep in mind that a theory of the moon’s
origin has to be (37) with two important facts. The first
fact is that the Earth (38) a lot of iron, most of it has an
iron core. But the moon contains (39) no iron. The second
fact is that other than the difference in iron content, the moon and Earth are
(40) of the same minerals, a (41) not
shared with any other planet or moon in our solar system. One of the earliest
theories of the moon’s origin, I called it the Capture Theory, proposes that the
moon was somehow captured by Earth’s gravitational force. This theory is
improbable, (42) , because it assumes that the moon and Earth
formed in different parts of the solar system. If this was true you would
(43) the moon’s composition to be much different from
Earth’s composition, just as all the other planets in the solar system are so
different from Earth. (44) . It is sometimes referred to as
the Mars Theory, because according to this theory, when Earth was still in
formation, (45) . The impact caused the cores of the two
planets to melt together and chunks of Earth’s crest to be thrown out into
space. These chunks came together to form the moon. Now, remember, Earth’s crust
is low in iron, because the iron is in Earth’s core, but high in various other
minerals. (46) .