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世界是恒定的。当然，暴风雨可能会吹倒一棵树，或者悬崖可能会被海浪慢慢吞噬，但海洋和山脉是永恒的。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，受到我们短暂的寿命的限制。然而，海洋和山脉也有寿命，而且寿命更长。仅在一万年前，加拿大的大部分地区还被冰覆盖。我们今天看到的一切要么不在这里，要么，如果它又大又坚固，那就在冰下。我们走得越远，事情就越不同。两千七亿年前，加拿大中部地区由类似于加勒比地区的火山岛组成；北美并不存在；世界海洋主宰着这个星球；最高级的生命是细菌；大气中没有氧气，但有大量二氧化碳。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，在加拿大中部大片地区以基岩的形式出现。我的研究利用沉积岩中留下的线索来探索地球年轻时的地理状况。我对 2.7 至 1800 万年前的大气和海洋的组成特别感兴趣，当时进行光合作用的生物体首次开始向大气和海洋添加大量氧气。我分析了沉积岩中的矿物质，这些矿物质是由当时海洋中沉淀的化学物质形成的。这些矿物质生长在海底，现在包含在二十亿年前的沉积岩中。矿物质的成分为我提供了所需的信息，以得出关于海洋化学如何随时间发展的结论。

Most people tend to view the natural world as constant. Sure, 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 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 Carribean region; North America did not exist; a world ocean dominated the planet; the most advanced life were 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 discouver 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 2.7 to 1.8 thousand million years ago when photosynthesizing organisms first started to add significant amounts of oxygen to the atmosphere and oceans. I analyse minerals in sedimentary rock that formed from chemicals precipitated in the ocean at that time. These minerals grew on the bottom of the ocean and are now contained in two billion year old 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.