1.Genetic drift __________.A.refers to the slow process by which two or more viruses combine or exchange genetic material B.was implicated as a major cause of mass extinction events in the last 530 million years C.in the human population has greatly

1.Genetic drift __________.A.refers to the slow process by which two or more viruses combine or exchange genetic material B.was implicated as a major cause of mass extinction events in the last 530 million years C.in the human population has greatly
1.Genetic drift __________.
A.refers to the slow process by which two or more viruses combine or exchange genetic material
B.was implicated as a major cause of mass extinction events in the last 530 million years
C.in the human population has greatly increased as our global population eclipsed 7 billion
D.is more likely to occur in smaller populations than in larger ones
2.__________ refers to the development of many new species from a single ancestor in a relatively short time.
A Genetic drift
B Microevolution
C Adaptive radiation
D The founder effect
3.To the best of our knowledge,which of the following describes what Earth was like from about 4.6 to 3.8 billion years ago?
A.Frequent electrical storms crackled the atmosphere.
B.After a cooling period,living organisms first appeared 4.5 billion years ago.
C.The early atmosphere contained mostly nitrogen and oxygen.
D.An ozone layer protected Earth from ultraviolet radiation and made life possible.

1.Genetic drift __________.A.refers to the slow process by which two or more viruses combine or exchange genetic material B.was implicated as a major cause of mass extinction events in the last 530 million years C.in the human population has greatly
1、选D.
遗传漂变（genetic drift）由于抽样误差引起群体内等位基因频率随机变化的现象.常发生在小群体中,因为抽样误差的大小与样本含量的大小成反比——样本越小,误差越大.
2、C.
适应辐射(adaptive radiation)
同起源生物类群演化成多种不同类型的后代,以适应不同环境的现象.
3、D.
冥古宙 （大约46亿年前--38亿年前）
冥古宙（Hadean）是指自地球形成至距今38亿年前这段时期.其间包含三个代
CrypticEra（直译是神秘时代） ——45.677亿年前 +/-0.7百万年
关于这个年代目前一无所知,地球是在这个阶段成型的,地球的内部开始塌陷（就是密度较大的物质向球心集合,如果地球足够大就会通过这个过程变成一颗恒星）而熔液表面则开始凝固.这一形成过程约长5000万到一亿年.
BasinGroups（直译是盆地群） ——45.6717亿年前-41.50亿年前
冥古代的第二个阶段,这个阶段持续到距今40亿年前.这个阶段可能因为地球表面的大量盆地得名.目前已知地球上最古老的岩石就形成于这个阶段
Nectarian（酒神代） ——约为40亿年前 -39.75亿年前
冥古代的第三个阶段,这个阶段只有短短的2500万年,在这一阶段发生了席卷太阳系内圈的天文轰炸,大量的天体撞击地球,所以在这个阶段,地球上应该还在不断地产生新的盆地.
46亿年前,刚刚形成的地球是一个没有生命的世界.那时,天空中赤日炎炎,电闪雷鸣,地面上火山喷发,熔岩横溢.从火山中喷出的甲烷、氨、氢、水蒸气等气体包围在地球表面,形成了原始大气层.原始大气与现在的大气成分完全不同,没有氧,也没有臭氧层,太阳的紫外线直射到地面上.在紫外线、宇宙射线、闪电、高温等巨大的自然条件长期作用下,原始大气中的各种成分不断发生合成或分解反应,形成了多种简单的有机物,这就为原始生命的产生创造了物质条件.
后来（大约在39亿年前）,地球的温度逐渐降低,但火山的喷发仍然很频繁,地壳也发生了变化,有些地方隆起形成高原和山脉,有些地方下降形成洼地和山谷.同时,大气中的水蒸气不断增多.当水蒸气达到饱合状态,冷却以后,便成为雨水降落到地面,汇入洼地,形成原始海洋.原始大气中的简单有机物也随着雨水进入原始海洋.在原始海洋中,这些简单的有机物在一定条件下,不断地进行反应,经过极其漫长的岁月,逐渐形成了原始生命.因此,原始海洋是原始生命诞生的摇篮.
祝你开心如意!