Notes: 1  In 1997, MLB retired Jackie Robinson's number 42 meaning no other player in MLB could ever wear it. However, it was grandfathered to anyone who was currently wearing the number. 2  Mariano Rivera is the only Yankee to appear as an active player while wearing his retired number.
The Ordovician Period. The Ordovician Period lasted almost 45 million years, beginning 488.3 million years ago and ending 443.7 million years ago.* During this period, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern supercontinent Gondwana.
Getting To Know the Age: The Ordovician Period is in the Paleozoic Era, which is set in the Phanerozoic Eon. The period began approximately 510 million years ago and ended 440 million years ago, totaling 70 million years, or 1.52% of geologic time (Prothero). Possible nicknames: Ordo the Obvious, the Drama Queen.