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。一场风暴可能会把一棵树吹倒，或者一个海崖可能会被海浪慢慢地侵蚀掉，但是海洋和山脉被认为是永恒的。当人们以这种方式思考永远时，他们是从人类的角度来看待这个概念的，受到我们短暂寿命的限制。然而，海洋和山脉也有寿命，而且寿命更长。两万年前，加拿大大部分地区还被冰雪覆盖。我们今天看到的一切要么不在这里，要么，如果它是大而坚实的，全部或大部分都在冰下。我们越往前走，与现在的差异就越大。27亿年前，加拿大中部地区由类似于加勒比地区的火山岛组成;北美不存在;世界海洋主宰着地球;最先进的生命是细菌;大气层没有氧气。我们之所以知道这一点，是因为当时火山爆发形成的岩石，以及岛屿侵蚀产生的沉积岩，都是加拿大中部大面积地区的基岩。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形和沉积过程。我对30亿到140亿年前大气和海洋的组成特别感兴趣。大约在这段时间的中间，进行光合作用的生物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质，这些矿物质是由这一时期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。矿物的组成为我提供了所需的信息，以形成关于海洋-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如何随着时间的推移而变化。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.