Ancient Chinese astronomers referred to the five major planets by the names of the element they were associated with: Venus corresponds to Metal (gold); Jupiter to Wood; Mercury to Water; Mars to Fire; Saturn to Earth.
As with most astrological systems Chinese Astrologers believed a person’s destiny could be determined by the positions of the major planets, the positions of the Sun, Moon and comets and the person’s time of birth and the corresponding zodiac birth sign.
This complex system is based upon the twelve year cycle of the orbit of Jupiter. (11.86 years in reality but who is counting?}.
The combination of 5 elements × 12 animal zodiac signs creates a 60-year cycle, which starts with the Wood Rat and ends with Water Boar.
If the year ends in 8 it is Yang Earth. If the year ends in 9 it is Yin Earth.
Earth is associated with the center of all directions and things, any enclosures, the change of seasons, the planet Saturn, the color yellow. the digestive system, and the spleen and stomach.
Earth people are patient, militaristic, prudent, stable, reliable, hard-working, ambitious, stubborn, and very energetic. They are disciplined, tenacious, logical, usually governed by service and duty to others.
Earth Governs' Dragon, Rat, and Ox. but is the central balance of the elements and can lend qualities to all 12 animals as well.
Here is the simple Chinese character for earth in earth.