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

使用原位高精度 U-Pb 测年技术研究地球随时间的撞击历史

• 批准号: RGPIN-2019-05343
• 负责人: Kamo, Sandra
• 金额: $ 2.55万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=715501
• 关键词: Investigating; Earth; impact; history; through

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.

地球的早期历史(Hadean Eon)受到了撞击盆地在月球上记录的强烈陨石轰击的影响。对月球撞击熔体和陨石的测年结果表明，年龄范围从~4.2岁到~39亿年，主要集中在年龄谱的年轻端。撞击的证据并没有在地球的动态表面幸存下来。相反，我们依赖于任务返回的样本和陨石。这种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。轰击是不是开始于太阳系内部行星的形成，并持续到整个哈迪亚地区？或者像人们常说的那样，它仅限于一场晚期的、激烈的末期大灾难？世界各地约190个已知的撞击结构记录了地球随后的陨石撞击历史，但这些事件的准确年龄信息严重缺乏。这使得评估它们对地球进化历史的影响变得困难。 这项拟议的研究将使用铀-铅(U-铅)测年技术结合一种创新的提取技术来研究陨石对地球的影响历史，以分离地质背景下的矿物。月球和火星陨石以及小行星上的原位年龄将首次利用高精度U-Pb地质年代学的最新进展来确定，以建立精确的年龄，以帮助澄清我们早期轰击历史的时间跨度。这对于理解地球和其他行星是如何进化的，以及撞击通量率如何以及为什么会随着时间发生变化是至关重要的。它对理解生命的出现具有重要意义，生命的出现可能已经受到早期强烈轰炸的负面影响。 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。在撞击过程中结晶或同位素重置的矿物上，撞击坑形成的时间可以确定。年龄对于评估对生态圈的影响和确定通量速率是重要的，这可能对人类种群产生影响。已知至少有一次陨石撞击在白垩纪末期的一次大规模灭绝中发挥了作用。来自Impact(如布伦特、卡斯韦尔、Vredefort、切萨皮克湾和萨德伯里)的样品已在手中，并将进行研究，以确定它们的时间、目标岩石的年龄，以及撞击后热叠印的影响。 这项拟议的研究是一种新的方法，将使加拿大成为世界上独一无二的。关于撞击的高精度原位测年将建立在我的撞击测年历史的基础上。这些结果将推动行星演化领域的发展，并通过地层记录中的相关性帮助评估过去环境对影响的反应。这是加拿大独一无二的努力，将现代铀-铅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在一起。