听力文本

To prove it they thought they needed just two fossils.
他们认为证明这一观点只需要两块化石
They needed the first tetrapod, the very first land walking creature with four legs with five toes
他们需要找到第一只四足动物，第一只具备四肢和五趾的陆行动物
and they needed the fish from which it came, a fish that could grow legs.
他们还需要找到它起源的那条鱼，一条能长出腿的鱼
Find these two fossils, compare them and in the differences between them
找到这两块化石，对它们进行比较，根据它们之间的区别
we would learn the reason why a fish had developed legs.
我们就能了解鱼进化出腿的原因
They had one huge clue to set them off:
有一条重要线索引导科学家进行探寻
they knew this evolution must have happened 400 million years ago, in the Devonian era.
他们知道这一进化过程肯定发生在4亿年前的泥盆纪

The Devonian is so long ago that barely any rock can now be found from it, let alone fossils,
泥盆纪距今甚为久远，如今那个时代的岩层已难觅踪迹，更不用说化石了
but academics knew that before it nothing walked and after it everything did,
不过学者们知道，在此之前没有能行走的动物，而这之后却是谁都能行走
so the evolution of legs must have happened then and they thought they knew something else.
所以腿的进化必然发生在那个年代，而且他们还了解别的情况
Textbooks said it was a time of blistering heat when almost nothing could live on the land, not even plants.
教科书中记载当时的气候酷热难耐，任何生物都无法在陆地上生存，甚至连植物也不例外
It meant most life survived not on land but in the water.
也就是说大部分生物并非生活在陆地上，而是呆在水中
This was the age of fish and one of them, the one with the beginning of legs, was the first fossil they needed to find.
那是鱼的时代，而其中一条鱼拥有腿的雏形，那就是他们要找的化石。

词汇解析

1.in the differences between ...之间的差异
Brazil offers a case study in the differences between a middle class created by the state and one that owes more to the private sector.
关于国家催生的中产阶级和更多地归功于私营领域的中产阶级的种种差异，巴西提供了一个鲜活的研究案例。

2.let alone 更不必说
She can't ride a bicycle, let alone drive a car.
她连自行车都不会骑，更别说开小汽车了。

3.live on the land 居住在陆地上
We must think about the people who live on the land.
我们必须考虑一下住在这片土地上的人。

视频及简介

19世纪，英国生物学家赫胥黎在研究了尼安德特人的头骨以后，认为是一个具有猿脸的头骨，但决不是人与猿之间的中间缺环。这就告诉我们，人与猿之间的亲缘关系，似乎还应该有一环。1891年发现直立猿人（爪哇猿人）的骨胳，证明这个缺环确实是存在的。可是，日本的人类学家认为爪哇猿人尚不是真正的中间缺环。那么，在猿与人之间到底应该是什么样的一环呢？在埃塞俄比亚发现的早期人科动物化石，很可能是过渡物种。这一发现，弥补了原始人类进化中的一个“缺环”。