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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=738208
• 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（冥古宙）受到月球撞击盆地记录的强烈陨石轰击的影响。月球撞击融化物和陨石的年代测定显示年龄范围为约 4.2 至约 39 亿岁，其中年龄谱中年轻的一端占主导地位。地球动态表面上没有留下影响的证据。相反，我们依靠任务返回的样本和陨石。这些天体物质形成的精确时间顺序可以回答有关地球起源的基本问题。轰击是否是内太阳系行星形成的结果，并持续到整个冥古宙？或者正如人们普遍引用的那样，它仅限于一场晚期的、剧烈的“末期灾难”？世界各地大约 190 个已知的撞击结构记录了地球随后的陨石撞击历史，但严重缺乏这些事件的精确年龄信息。这使得评估它们对地球进化历史的影响变得困难。 拟议的研究将利用铀铅 (U-Pb) 测年法并结合创新的提取技术来研究地球的陨石撞击历史，以在地质背景下分离矿物。将首次利用高精度 U-Pb 地质年代学的最新进展来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，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如何演化，以及撞击通量率如何以及为何随时间变化至关重要。它对于理解生命的出现具有重要意义，生命可能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。撞击坑的时间可以根据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通量率非常重要，这可能对人口产生影响。已知至少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。来自撞击（例如布伦特、卡斯韦尔、弗里德堡、切萨皮克湾和萨德伯里）的样本已在手，将对其时间、目标岩石的年龄以及撞击后热叠印的影响进行研究。 拟议的研究是一种新方法，将使加拿大在世界上独一无二。对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。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。这是加拿大独特的努力，将现代 U-Pb 测年和纳米束矿物研究的发源地与唯一可用的微研磨矿物仪器结合起来。