一、概述
    the Old World是合成名词，意为“东半球(尤指欧洲)”。反之，the New World则是“西半球”，即美洲。Old-World（东半球的）和New-World（西半球的，美洲的）则是它们分别所对应的形容词。

二、旧大陆、东半球（the Old World）

  旧大陆是指在哥伦布发现新大陆之前，欧洲认识的世界，包括欧洲、亚洲和非洲（全体被称为亚欧非大陆或世界岛，但不包括英伦三岛、日本、马达加斯加和马来礁岛）。与此相区别，新大陆主要指美洲大陆。

虽然在那个时候，亚洲和非洲内陆还不为欧洲人所知，但是欧洲人已经知道远到日本和南非的亚洲和非洲的存在，因此也被认为是旧大陆。大洋洲和南极洲即不明确属于旧大陆，也不属于新大陆，这是由于旧大陆和新大陆是在发现大洋洲和南极洲之前提出的。

    在生物学上的使用，旧大陆的生物是指那些在欧亚大陆、非洲、大洋洲发现的生物，新大陆的生物是指那些在美洲发现的生物。在生物学上，把大洋洲划入旧大陆反映了物种在进化过程中传播散布的一般形式。

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旧大陆地图 （托勒密Ptolemy，15世纪）

The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" (i.e., the Americas).The Old World comprises Africa, Asia, and Europe (collectively known as Afro-Eurasia), plus surrounding islands (or at least those parts which were known to classical geography before the 15th century).

The concept of the three continents in the Old World goes back to classical antiquity. Their boundaries as defined by Ptolemy and other geographers of antiquity were drawn along the Nile and Don rivers. This definition remained influential throughout the Middle Ages and the Early Modern period.

三、新大陆、西半球 （the New World）
    新大陆是西半球的另一个名称，有时指美洲和大洋洲（澳大拉西亚）。该术语最早源于16世纪。

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新大陆，绿色部分

The New World is one of the names used for the Western Hemisphere, specifically the Americas and

sometimes Oceania (Australasia). The term originated in the early 16th century, shortly after America was discovered by European explorers, expanding the geographical horizon of the people of the European middle Ages, who had thought of the world as consisting of Europe, Asia, and Africa only: collectively now referred to as the Old World. The Americas were also referred to as the "fourth part of the world".

整理自维基百科、沪江