Global warming and the Late Permian mass extinction event

地球上的生命受到了一系列大规模灭绝事件的影响，在这些事件中，陆地和海洋中的很大一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恐龙灭绝事件。然而，与化石记录中记载的最严重的大灭绝事件——晚二叠纪事件相比，白垩纪末期的事件相形见绌。晚二叠纪事件发生在2.5亿年前，在此期间，海洋和陆地上至少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要事件。还有很多事情我们不知道，特别是关于这场灾难的原因。没有确凿的证据表明当时发生了陨石撞击，但这一事件似乎与今天西伯利亚陆地上最大的火山熔岩喷发同时发生。大多数科学家现在认为，西伯利亚火山爆发释放的二氧化碳在大气中慢慢积聚。二氧化碳是一种众所周知的温室气体。随着气温开始上升，科学家们认为地球遭受了“失控的温室效应”，全球变暖失去了控制。科学家们估计，巨大的生命损失发生在全球气温上升5-6摄氏度的时期，这是对下个世纪气温上升的预测的上限。然而，这个5-6度的温度估计有潜在的问题。这些数字来自1980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。我们需要找到另一种方法来估算过去的温度变化。一种方法是分析腕足类海洋动物化石的壳。这些动物生活的海水的地球化学特征被保存在它们的贝壳中，通过对保存完好的贝壳的分析，我们可以重建古代海水的温度。腕足动物有两种：不节肢和节肢。有节肢的腕足动物在二叠纪非常常见，但现在却非常罕见，它们的方解石壳经常被用来重建过去的气候。不发音动物包括腕足动物Lingula，它是一个“活化石”，在过去的重大灭绝事件中幸存下来。在晚二叠纪灭绝事件发生之前，尤其是之后，Lingula非常普遍。最近的研究首次表明，Lingula贝壳的某些部分（由方解石组成的部分）也保留了该动物生活的海水的地球化学特征。直到现在，还没有人使用Lingula来重建过去的气候。我们将在意大利北部的腕足动物灭绝事件发生之前和之后收集。从初步工作中我们已经知道，那里的岩石暴露得很好，含有大量的腕足动物化石，而且这些腕足动物保存得很好。使用地球化学技术，我们将检查我们收集的每一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。我们期望在灭绝事件中看到变化，但它会上升5-6度吗？也许气温变化比科学家们目前认为的更严重，或者更轻微。这一重要信息将有助于我们更好地了解地球历史上最大规模的物种灭绝事件，并有助于我们更好地了解过去的气候变化。

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.