Investigating Earth's impact history through time using in situ high precision U-Pb dating

地球的早期历史（冥古宙）受到月球撞击盆地记录的强烈陨石轰击的影响。月球撞击熔体和陨石的年代测定表明，年龄在~ 42 ~ ~ 39亿年之间，在年龄谱的年轻端占优势。撞击的证据并没有在地球动态的表面上留存下来。相反，我们依赖于任务返回的样本和陨石。这些天体物质形成的精确时间序列可以回答有关地球起源的基本问题。轰击是否作为内太阳系行星形成的结果而开始并持续到整个冥古宙？还是像人们常说的那样，仅仅局限于“一场晚期的、激烈的终极大灾难”？地球随后的陨石撞击历史被世界上约190个已知的撞击结构所记录，但这些事件的精确年龄信息严重缺乏。这使得评估它们对地球进化史的影响变得困难。***拟议的研究将利用铀-铅（U-Pb）测年结合一种创新的提取技术来分离地质背景下的矿物，研究地球的陨石撞击历史。利用高精度U-Pb地质年代学的最新进展，将首次确定月球和火星陨石以及小行星的原位年龄，以建立精确的年龄，帮助阐明我们早期轰击历史的时间跨度。这是理解地球和其他行星如何进化的基础，也是理解撞击速率如何以及为什么随时间而变化的基础。这对理解生命的出现有意义，生命的出现可能受到早期强烈撞击的负面影响。在陆地记录中，陨石撞击在地质和生物记录中留下了其影响的痕迹。陨石坑形成的时间可以通过在撞击过程中结晶或同位素重置的矿物来确定。年龄对于评估对生态圈的影响和确定可能对人口产生影响的通量率非常重要。已知至少有一次陨石撞击在白垩纪末期的一次大灭绝中起了作用。来自撞击的样本（例如Brent、Carswell、Vredefort、Chesapeake Bay和Sudbury）已经到手，并将对它们的时间、目标岩石的年龄以及撞击后热套印的影响进行调查。拟议中的研究是一种新方法，将使加拿大在世界上独树一帜。高精度的撞击现场测年将建立在我的撞击测年史上。结果将推动行星演化领域的发展，并有助于通过地层记录的相关性评估过去环境对影响的响应。这是加拿大独特的努力，将现代U-Pb测年和纳米束矿物调查的发源地与唯一可用的微磨矿物仪器结合起来。*****

Earth's early history (Hadean Eon) was affected by intense meteorite bombardment recorded on the Moon by impact basins. Dating of lunar impact melt and meteorites indicates ages ranging from ~4.2 to ~3.9 billion years old, with a preponderance towards the young end of the age spectrum. Evidence of the impacts have not survived on Earth's dynamic surface. Instead, we rely on mission-returned samples and meteorites. The precise time sequence of formation of such astro-materials can answer fundamental questions about Earth's beginnings. Did bombardment begin as a consequence of planet formation in the inner Solar System and continue throughout the Hadean? Or was it restricted to a late, intense terminal cataclysm', as commonly cited? Earth's subsequent meteorite impact history is documented by ~190 known impact structures around the world, but precise age information for these events is severely lacking. This makes it difficult to assess their influence on Earth's evolutionary past. *** The proposed research will investigate the meteorite impact history of Earth using uranium-lead (U-Pb) dating in combination with an innovative extraction technique to isolate minerals within their geological context. For the first time, in situ ages on Lunar and Martian meteorites, and asteroids, will be determined using the latest advances in high precision U-Pb geochronology to establish precise ages to help clarify the time span of our early bombardment history. This is fundamental in understanding how the Earth and other planets evolved, and to how and why the impact flux rate changed through time. It has implications to understanding the emergence of life, which may have been negatively affected by early intense bombardment. *** In the terrestrial record, meteorite impacts have left traces of their effects in the geological and biological records. The time of impact cratering can be determined on minerals that crystallized, or were isotopically reset, during the impact process. Ages are important for assessing effects on the ecosphere, and to establishing flux rates, which can have implications for human populations. At least one meteorite impact is known to have played a role in a major mass extinction at the end of the Cretaceous. Samples from impacts (e.g., Brent, Carswell, Vredefort, Chesapeake Bay, and Sudbury) are in hand and will be investigated for their timing, age of target rocks, and effects of post-impact thermal overprinting. *** The proposed research is a new approach and will position Canada as unique in the world. High precision in situ dating on impacts will build upon my history of impact dating. Results will advance the field of planetary evolution and help evaluate past environmental response to impacts through correlations in the stratigraphic record. It is a uniquely Canadian effort in uniting the birthplace of modern U-Pb dating and nanobeam mineral investigation with the only available instrument for micro-milling minerals.*****