The oldest earrings were found in the royal graves in Iraq.  
Earrings have come in and out of fashion over the centuries.  During the Renaissaince era women wore elaborate wigs, hairstyles and clothing with collars that covered the ears.  In the 17th century, women wore their hair back and earrings were seen again.  In the early parts of the 18th century women wore large bonnets with wide ribbons and again the ears were obscured. In the latter half of the 18th century through the 19th century the bonnets came off, the hair went up and lo and behold, earrings again.  
In the early part of the 20th century, Victorians thought that piercing the ears was uncouth.  Necessity being the mother of invention, the screwback which was invented in the 1930's.  Screw backs and other type of clip backs ruled the earring world until the 1970's when ear piercing became a fad again.
Now days, most earrings are made for pierced ears, but if you don't like poking holes in yourself, you can stil find clip ons, contemporary and vintage, to suit your individual tastes and fashion needs.

(C) Judith Barnes 2007