奥陶纪 Ordovician

构造运动

Sea levels were high during the Ordovician; in fact during the Tremadocian, marine transgressions worldwide were the greatest for which evidence is preserved in the rocks

在奥陶纪，海平面很高；事实上，在奥陶世，那些保留在岩石里的证据证明了那时曾发生过世界范围内最大的海侵。

During the Ordovician, the southern continents were collected into a single continent called Gondwana. Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole.

在奥陶纪，南部大陆聚集在一起形成一个单一的大陆，被称作冈瓦纳古大陆。冈瓦纳古大陆起源于赤道附近地区，随着时间的推移，逐渐向南极漂去。

Early in the Ordovician, the continents Laurentia (present-day North America), Siberia, and Baltica (present-day northern Europe) were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move towards Laurentia later in the period, causing the Iapetus Oceanto shrink between them.

在早奥陶世，劳伦大陆（现今北美地区），西伯利亚和波罗地大陆（现今北欧地区）仍然是相互独立的大陆（自从早些时候超大陆潘诺西亚分裂以来），但是后来波罗地大陆开始朝着劳伦大陆运动，引起它们之间的巨神海开始收缩。

The small continent Avalonia separated from Gondwana and began to head north towards Baltica and Laurentia. The Rheic Ocean between Gondwana and Avalonia was formed as a result.

小大陆阿瓦隆尼亚大陆从冈瓦纳古大陆中分离出来，并且开始向北朝着波罗地大陆和劳伦大陆运动，结果在形成了冈瓦纳古大陆和阿瓦隆尼亚大陆之间形成了瑞亚克洋。

A major mountain-building episode was the Taconic orogeny that was well under way in Cambrian times. In the beginning of the Late Ordovician, from 460 to 450 Ma, volcanoes along the margin of the Iapetus Ocean spewed massive amounts of carbon dioxide into the atmosphere, turning the planet into a hothouse.

主要的造山运动是在寒武统顺利进行的塔科尼克造山运动。在晚奥陶世开始时，从460到450Ma，沿着古大西洋的火山喷出了大量的二氧化碳到大气中，直接把地球变成了温室。

These volcanic island arcs eventually collided with proto North America to form the Appalachian mountains. By the end of the Late Ordovician these volcanic emissions had stopped. Gondwana had by that time neared or approached the pole and was largely glaciated.

这些火山岛弧最终和来自于阿帕拉契山脉的原始北美大陆相碰撞。到晚奥陶世末期的时候，这些火山喷发物已经停止了。直到那时冈瓦纳古大陆已经接近或者到达了极点，几乎被大范围地冰封。

气候特征

 

At the beginning of the period, around 485.4 ± 1.9 million years ago, the climate was very hot due to high levels of CO2, which gave a strong greenhouse effect. The marine waters are assumed to have been around 45 °C (113 °F), which restricted the diversification of complex multi-cellular organisms.

奥陶纪开始时，由于高浓度二氧化碳产生的强烈温室效应，气候非常炎热。据推理假设，海洋水域温度达到45摄氏度，从而限制了多细胞生物的多样化。

But over time, the climate became cooler, and around 460 million years ago, the ocean temperatures became comparable to those of present-day equatorial waters.

但随时间流逝，气候逐渐变凉爽，约460百万年前的海洋水温与现在赤道附近的水温大致相当。

As the Ordovician progressed, we see evidence of glaciers on the land we now know as Africa and South America. At the time these land masses were sitting at the South Pole, and covered by ice caps.

奥陶纪末期曾有一次大冰期the Hirnantian glaciation，气温持续下降。我们在现在的非洲、南美洲可以看到这次冰川留下的痕迹，当时这些陆地位于南极点，并且覆着冰盖。

生物特征

 

海生生物空前发展。化石以三叶虫、笔石、腕足类、棘皮动物中的海林檎类、软体动物中的鹦鹉螺类最常见，苔藓虫、牙形石、腔肠动物中的珊瑚、棘皮动物中的海百合、节肢动物中的介形虫和苔藓动物等也很多。节肢动物中的板足鲎类和脊椎动物中的无颌类[如甲胄鱼类]等均已出现。低等海生植物继续发展，淡水植物据推测可能在奥陶纪也已经出现。

在奥陶纪早期，约5亿年前，首次出现了可靠的陆生脊椎动物——淡水无颚鱼。奥陶纪中期，在北美落基山脉地区出现了原始脊椎动物异甲鱼类——星甲鱼和显褶鱼，在南半球的澳大利亚也出现了异甲鱼类。植物仍以海生藻类为主。

腕足动物在这一时期奥演化迅速，大部份的类群均已出现，无铰类、几丁质壳的腕足类逐渐衰退，钙质壳的有铰类则盛极一时；鹦鹉螺进入繁盛时期，它们身体巨大是奥陶纪的海洋中凶猛的肉食性动物；

由于大量食肉类鹦鹉螺类的出现，为了防御，三叶虫在胸、尾长出许多针刺，以避免食肉动物的袭击或吞食。珊瑚在中奥陶世开始出现，复体的珊瑚虽说还较原始，但已能够形成小型的礁体。由于海洋无脊椎动物的大发展，在前寒武纪时非常繁盛的叠层石在奥陶纪时急剧衰落。

奥陶纪时期的海洋生物是现代动物的最早祖先最大的新出现的动物是像萨卡班巴鱼这样的无颌类。无颌类，例如发观于南美的萨卡班巴鱼，是地球上最早的脊椎动物之一。这一时期仍然没有任何动物种类生活在陆地上。