Sedimentology of Precambrian Depositional Systems: Understanding the Earth's Surface in Deep Time

*大多数人倾向于认为自然界是恒定的。风暴可能会吹倒一棵树，或者悬崖可能会被海浪慢慢冲走，但海洋和山脉被视为永恒。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，受到我们短暂的寿命的限制。然而，海洋和山脉也有寿命，而且寿命要长得多。仅仅两万年前，加拿大的大部分地区都被冰覆盖着。我们今天看到的一切要么不在这里，要么如果它很大很坚固，就全部或大部分在冰下。我们往前走得越远，与现在的差距就越大。27亿年前，加拿大中部地区由类似加勒比海地区的火山岛组成；北美并不存在；世界海洋主导着地球；最高级的生命是细菌；大气中没有氧气。我们知道这一点是因为此时火山喷发形成的岩石和岛屿侵蚀产生的沉积岩作为基岩出现在加拿大中部大片地区的地下。我的研究使用在沉积岩中留下的线索来发现当时地球还是一颗年轻的行星时，地理上是什么样子的，沉积过程是如何运作的。我特别感兴趣的是3.0到14亿年前这段时间的大气和海洋的组成。大约在这段时间的中期，光合作用的有机体向大气和海洋中增加了大量的氧气。我分析了沉积岩中的矿物，这些沉积岩是在这段时间里在海洋中沉淀下来的化学物质形成的。这些矿物生长在海底，现在包含在沉积岩中。矿物的组成为我提供了所需的信息，以得出关于海洋-大气系统的化学如何随时间发展的结论。这项工作的重要性不仅限于了解海洋和大气是如何随着时间的推移而变化的。地球表面的化学物质是地球上各种形式生命进化的主要控制因素。了解海洋-大气化学对于解开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 viewed as 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 twenty 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 all or mostly under the ice. The further back in time we go, the greater the difference from the present. 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. 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 and what sedimentary processes were operating, when the Earth was a young planet. I am particularly interested in the composition of the atmosphere and ocean during the time period 3.0 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 analyse 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 ocean-atmosphere system 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 unraveling life's early history.