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。

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

但有一些科学家认为伽玛射线爆发可能四十五亿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（44000万以）和泥盆纪（36500万以）分别消灭了大约80%——85%的物种。

440 million years ago was the The Ordovician extinction.

4.4亿奥陶纪灭绝。

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

在奥陶纪之，陆地生命 可能仅限于生物。

This is known as the Great Ordovician Biodiversification Event.

这被称为奥陶纪生物多样性大 事件。

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

7亿，在奥陶纪， 第一批植物开始生活在陆地上。

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

但在晚奥陶世时期，化石记录中出现了第二种海蝎亚目——广翅亚目。

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

进入奥陶纪时期， 大约4.85亿，期海百合分化出了数千种形态。

The Ordovician period also saw the advent of more active suspension feeders, like the giant, filter-feeding anomalocarid Aegirocassis.

奥陶纪时期出现了更多活跃的悬垂摄食者，比如巨型滤食动物艾吉罗卡西斯。

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发生在 4.5 亿的晚奥陶世大灭绝。

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

到了寒武纪过渡到奥陶纪时，头足类动物迎来了黄金时代。

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

奥陶纪的内角贝类头足类动物当时最大的动物，体长可达惊人的6米。

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

随着奥陶纪的推进，头足类动物开始离开浅水区，探索开阔的海洋。

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

这次被称为奥陶纪-志留纪灭绝事件的双重打击，消灭了大约25%的所有分类科，包括约一半的三叶虫科。

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4.88亿的历史——这将它们归类到奥陶纪。

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

这种鱼生活在现在的玻利维亚沿海水域，大约4.7亿的奥陶纪时期。

Crinoids became the most abundant echinoderms of the Ordovician, and some were the ancestors of today's stalkless feather stars and stalked sea lilies.

海百合成为了奥陶纪最丰富的棘皮动物，其中一些今天无茎羽状海百合和有茎海百合的祖先。

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，他最钟爱的一种名叫三叶虫的海生动物。那种动物一度充满奥陶纪的海洋，但已不复存在，除了以化石的形式。