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.
The transition from the peak of the last ice age around 20,000 years ago to the start of the modern interglacial period (the Holocene) around 10,000 years ago, was interrupted by a sharp return to near-glacial conditions during the Younger Dryas period.This period lasted from about 13,000 years ago to 11,500 years ago.he transition from the peak of the last ice age around 20,000 years ago to the start of the modern interglacial period (the Holocene) around 10,000 years ago, was interrupted by a sharp return to near-glacial conditions during the Younger Dryas period.