The first one that happens is at the end of the Ordovician period around 400 million years ago.

第一次大灭绝发生在奥陶纪末期，大约 4 亿年前。

But some also believe that a gamma ray burst was responsible for the Ordovician extinction around 455 million years ago.

但是也有一些认伽玛射线爆发可能是四十五亿年前奥陶纪大灭绝的罪魁祸首。

The Ordovician (440 million years ago) and Devonian (365 million) each wiped out about 80 to 85 percent of species.

奥陶纪（44000万年以前）和泥盆纪（36500万年以前）分别消灭了大约80%——85%的种。

440 million years ago was the The Ordovician extinction.

4.4亿年前是奥陶纪大灭绝。

This is known as the Great Ordovician Biodiversification Event.

这被称奥陶纪生多样性大 事件。

Before the Ordovician, terrestrial life was probably limited to microbes.

在奥陶纪之前，陆地生命 可能仅限于微生。

Heading into the Ordovician Period, around 485 million years ago, eocrinoids diversified into thousands of forms.

进入大约 4.85 亿年前的奥陶纪时期，类分泌多样化数千种形式。

470 million years ago, in the Ordovician Period, the first plants began to live on land.

7亿年前，在奥陶纪， 第一开始生活在陆地上。

The very first mass extinction we know of is the Late Ordovician extinction that took place 450 million years ago.

我们所知道的第一次大灭绝是发生在 4.5 亿年前的晚奥陶世大灭绝。

By the time the Cambrian had segued into the Ordovician, cephalopods had entered a golden age.

当寒武纪进入奥陶纪时，头足类动进入了黄金时代。

Plants first began colonizing the land during the  Ordovician period, about 470 million years ago.

大约 4.7 亿年前的奥陶纪时期，首先开始在这片土地上定居。

The fossils they found were about 488 million years old -- which put them in the Ordovician.

他们发现的化石大约有 4.88 亿年的历史——这使它们处于奥陶纪。

This twofold impact known as the Ordovician-Silurian Extinction, wiped out about 25% of all taxonomic families, including about half of trilobite families.

这种被称奥陶纪-志留纪灭绝的双重影响消灭了大约 25% 的所有分类，包括大约一半的三叶虫。

But, during the Late Ordovician, a second suborder of sea scorpion emerges in the fossil record — the Eurytperina.

但是，在晚奥陶世期间，化石记录中出现了海蝎的第二个亚目——Eurytperina。

The Ordovician endoceratids cephalopods were the biggest animals of their time, reaching an impressive 6 meters in length.

奥陶纪的头足类动是当时最大的动，身长可达 6 米， 令人印象深刻。

And as the Ordovician progressed, cephalopods began to leave the shallows to explore the open ocean.

随着奥陶纪的进展，头足类动开始离开浅滩探索开阔的海洋。

And there are extensive black shale deposits in places like China and northern Africa, dating to the late Ordovician.

在中国和北非等地有大量黑色页岩矿床，可追溯到晚奥陶世。

But his first love is a type of marine creature called trilobites that once teemed in Ordovician seas but haven't existed for a long time except in fossilized form.

但是，他最钟爱的是一种名叫三叶虫的海生动。那种动一度充满奥陶纪的海洋，但早已不复存在，除了以化石的形式。

The period right after the Cambrian is the Ordovician, and this is when paleontologists saw a major change in the composition of animal life.

紧接寒武纪之后的时期是奥陶纪，古生正是在这个时期发现动生命的构成发生重大变化。

This fish lived in the coastal waters of what's now Bolivia, during the Ordovician Period, some 470 million years ago.

大约 4.7 亿年前的奥陶纪时期，这种鱼生活在现在玻利维亚的沿海水域。