Precambrian Sedimentary Assemblages: Keys to Understanding Ocean-Atmosphere Evolution and Tectonic Processes on the Young Earth

大多数人倾向于认为自然界是不变的。暴风雨可能会吹倒一棵树，悬崖可能会被海浪慢慢吞噬，但海洋和山脉被认为是永恒的象征。当人们以这种方式思考永恒时，他们是从人类的角度来看待这个概念的，因为我们的寿命很短。然而，海洋和山脉也有寿命，而且寿命要长得多。仅仅在一万年前，加拿大的大部分地区还被冰覆盖着。我们今天看到的一切要么不在这里，要么就在冰下，如果它又大又坚固的话。时间越久远，事物就越不同。27亿年前，加拿大中部地区由火山岛组成，类似于加勒比海地区；北美还不存在；世界海洋主宰着地球；最先进的生命是细菌；大气中没有氧气，却有大量的二氧化碳。我们之所以知道这一点，是因为当时火山喷发形成的岩石，以及岛屿侵蚀产生的沉积岩，在加拿大中部的大片地区形成了基岩。我的研究利用沉积岩中留下的线索来发现地球年轻时的地理状况。我对280到140亿年前的大气和海洋的组成特别感兴趣。大约在这一时期的中期，光合作用的生物向大气和海洋中添加了大量的氧气。我分析沉积岩中的矿物质，这些矿物是在这段时间里由海洋中沉淀的化学物质形成的。这些矿物生长在海底，现在包含在沉积岩中。这些矿物的组成为我提供了必要的信息，使我能够就海洋的化学成分是如何随着时间的推移而发展得出结论。这项工作的重要性并不局限于了解海洋和大气是如何随着时间的推移而变化的。地球表面的化学成分是地球上各种生命形式进化的主要控制因素。了解海洋大气化学对于揭示生命的早期历史至关重要。

Most people tend to view the natural world as constant. A storm may blow a tree down or a bluff may be slowly eaten away by the waves, but the oceans and the mountains are looked upon as representing forever. When people think of forever in this way, they are approaching the concept from a human point of view, limited by our short lifespans. However, the oceans and mountains also have lifespans and these are much longer. Only ten thousand years ago most of Canada was covered by ice. Everything we see today was either not here or, if it was large and solid, was under the ice. The further back in time we go, the more different things were. Two thousand seven hundred million years ago the central area of Canada consisted of volcanic islands similar to the Caribbean region; North America did not exist; a world ocean dominated the planet; the most advanced life was bacteria; and the atmosphere had no oxygen, but lots of carbon dioxide. We know this because the rocks that were formed at this time from volcanic eruptions, and the sedimentary rocks produced by the erosion of the islands, occur as bedrock under large areas of central Canada. My research uses clues left behind in sedimentary rocks to discover what the geography looked like when the Earth was a young planet. I am particularly interested in the composition of the atmosphere and ocean during the time period 2.8 to 1.4 thousand million years ago. In approximately the middle of this time period photosynthesizing organisms added significant amounts of oxygen to the atmosphere and oceans. I analyze minerals in sedimentary rocks that formed from chemicals precipitated in the ocean during this time period. These minerals grew on the bottom of the ocean and are now contained in sedimentary rocks. The composition of the minerals provides me with the information I need to form conclusions on how the chemistry of the oceans developed through time. The importance of this work is not limited to understanding how the oceans and atmosphere were transformed over time. The chemistry of the surface of the Earth was a major control on the evolution of various forms of life on Earth. Understanding ocean-atmosphere chemistry is essential to unravelling life's early history.