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末期，大约 4 亿年。

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

但是也有一些科学家认为伽玛射线爆发可能是四十五亿年大灭绝罪魁祸首。

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

（44000万年以）和泥盆（36500万年以）分别消灭了大约80%——85%物种。

440 million years ago was the The Ordovician extinction.

4.4亿年是大灭绝。

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

在之，地生命 可能仅限于微生物。

This is known as the Great Ordovician Biodiversification Event.

这被称为生物多样性大 事件。

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

进入大约 4.85 亿年时期，类分泌物多样化为数千种形式。

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

7亿年，在， 第一批植物开始生活在地上。

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

我们所知道第一次大灭绝是发生在 4.5 亿年晚世大灭绝。

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

大约 4.7 亿年时期，植物首先开始在这片土地上定居。

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

当寒武进入时，头足类动物进入了黄金时代。

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

他们发现化石大约有 4.88 亿年历史——这使它们处于。

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

这种被称为-志留灭绝双重影响消灭了大约 25% 所有分类科，包括大约一半三叶虫科。

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

头足类动物是当时最大动物，身长可达 6 米， 令人印象深刻。

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

但是，在晚世期间，化石记录中出现了海蝎第二个亚目——Eurytperina。

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

随着进展，头足类动物开始离开浅滩探索开阔海洋。

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，他最钟爱是一种名叫三叶虫海生动物。那种动物一度充满海洋，但早已不复存在，除了以化石形式。

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

紧接寒武之后时期是，古生物学家正是在这个时期发现动物生命构成发生重大变化。

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

时期还出现了更活跃悬浮式捕食者，例如巨大滤食性奇虾 Aegirocassis。