Global warming and the Late Permian mass extinction event

地球上的生命受到了许多大规模灭绝事件的影响，陆地和海洋中的大部分动物和植物永远消失了。一个著名的例子是6500万年前白垩纪末期灭绝恐龙的灭绝事件。然而，与化石记录中记录的最严重的大规模灭绝事件：晚二叠世事件相比，白垩纪末的事件相形见绌。晚二叠世事件发生在2.5亿年前，在此期间，海洋和陆地上至少有80%甚至90%以上的物种灭绝。近年来，越来越多的科学家开始研究这一地球历史上的重大事件。我们仍有许多不了解的情况，特别是关于这场灾难的原因。当时并没有陨石撞击的证据，但这一事件似乎与现今西伯利亚发生的最大规模的火山熔岩喷发相吻合。大多数科学家现在认为西伯利亚的火山爆发释放了二氧化碳，二氧化碳在大气中慢慢积累。二氧化碳是一种众所周知的温室气体。随着气温开始上升，科学家认为地球遭受了“失控的温室效应”，全球变暖失控。科学家们估计，在全球气温上升5-6摄氏度的时候，发生了巨大的生命损失，这是对下一个世纪气温上升的预测范围的上限。然而，这个5-6度的温度估计存在潜在的问题。这些数字来自20世纪80年代末对奥地利南部石灰岩的地球化学研究。不幸的是，这些岩石保存得不是很好，根据我们对地球化学的现代理解，我们现在认为这些估计是错误的。我们需要找到一种替代方法来估计过去的温度变化。其中一种方法是分析腕足类海洋动物化石的贝壳。这些动物生活的海水的地球化学特征被保存在它们的外壳中，通过分析保存完好的外壳，我们可以重建古代海水的温度。腕足动物有两种类型：无关节和有关节。有关节的腕足动物在二叠纪非常常见，但在今天却非常罕见，它们的方解石壳经常被用来重建过去的气候。无关节动物包括腕足动物舌形动物，它是一种“活化石”，在过去的大灭绝事件中幸存下来。小舌在晚二叠世灭绝事件之前和之后非常常见。最近的研究首次表明，舌形贝的一部分（由方解石组成的部分）也保留了这种动物生活的海水的地球化学特征。到目前为止，还没有人使用Lingula来重建过去的气候。我们将在北方意大利收集灭绝事件之前和之后的腕足动物。从初步工作中我们已经知道，那里的岩石暴露良好，含有丰富的腕足动物化石，腕足动物保存完好。利用地球化学技术，我们将检查我们收集的每个化石壳的保存情况，并将使用保存最好的化石壳来估计动物实际生活的水温。我们希望通过灭绝事件看到一个变化，但它会上升5-6度吗？也许温度变化比科学家目前认为的更严重，或更少。这些重要信息将有助于提高我们对地球历史上最大规模灭绝事件的理解，并有助于提高我们对过去气候变化的理解。

Life on Earth has been affected by a number of mass extinction events, where a significant proportion of the animals and plants, on land and in the sea, disappeared forever. One well-known example is the extinction event that wiped out the dinosaurs at the end of the Cretaceous Period, 65 million years ago. The end-Cretaceous event is dwarfed, however, by the most severe mass extinction event recorded in the fossil record: the Late Permian event. The Late Permian event happened just over 250 million years ago, during which time at least 80% and perhaps more than 90% of species in the oceans and on land became extinct. In recent years an increasing number of scientists have started to investigate this important event in earth history. There is still much that we do not know, especially regarding the cause(s) of the catastrophe. There is no good evidence of a meteorite impact at that time, but the event does seem to coincide with the largest outpourings of volcanic lava on land which occurred in present-day Siberia. Most scientists now think that the volcanic eruptions in Siberia released carbon dioxide that slowly built up in the atmosphere. Carbon dioxide is a well-known greenhouse gas. As temperatures began to rise, scientists think that the Earth suffered a 'runaway greenhouse' and global warming spiralled out of control. Scientists estimate that the huge loss of life occurred during a time when global temperatures rose by 5-6 degress C, which is in the upper range of predictions made for temperature increase in the next century. There are, however, potential problems with this 5-6 degree temperature estimate. The numbers derive from geochemical studies of limestone rocks from southern Austria made in the late 1980s. Unfortunately, these rocks are not very well preserved, and with our modern understanding of geochemistry we now think that these estimates are wrong. We need to find an alternative way of estimating temperature change in the past. One way is to analyse the shells from fossil marine animals called brachiopods. The geochemical signature of the seawater in which these animals lived is preserved within their shells, and from analysis of well-preserved shells we can reconstruct the temperature of the ancient seawater. There are two types of brachiopod: inarticulate and articulate. The articulate brachiopods were very common in the Permian, but much rarer today, and their calcite shells are often used to reconstruct past climate. The inarticulates include the brachiopod Lingula, which is a 'living fossil', having survived the major extinction events of the past. Lingula is very common before and especially just after the Late Permian extinction event. Recent work has shown for the first time that parts of the Lingula shell (the portion made of calcite) also preserve the geochemical signature of the seawater in which the animal lived. Until now, nobody has used Lingula to reconstruct past climate. We will collect brachiopods from just before and just after the extinction event from northern Italy. We already know, from preliminary work, that the rocks are well exposed there, contain abundant fossil brachiopods, and that the brachiopods are well-preserved. Using geochemical techniques we will examine the preservation of each fossil shell we collect, and will use the best preserved ones to produce estimates of the water temperatures in which the animals actually lived. We expect to see a change through the extinction event, but will it be a rise of 5-6 degrees? Perhaps the temperature change was more, or less, severe than scientists presently think. This important information will help improve our understanding of the greatest mass extinction event in our planet's history and will help improve our understanding of past climate change.