The nature of the Ediacaran to early Cambrian geomagnetic field

埃迪卡拉纪至早寒武世地磁场的性质

• 批准号: 1520681
• 负责人: John Tarduno
• 金额: $ 29.55万
• 依托单位: University of Rochester
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1520681&HistoricalAwards=false
• 关键词: nature; Ediacaran; early; Cambrian; geomagnetic

The suggestion that the entire solid Earth rotated by 90 degrees, approximately 565 million years ago, and that this event sparked the explosion of life on the planet (when most existing animal phyla and classes first appeared), is one of the most controversial hypotheses in the geosciences. Ultimately, the veracity of this idea rests on how well the past geomagnetic field is recorded in ancient rock samples (the purview of the discipline of paleomagnetism). The PIs have developed a method for obtaining paleomagnetic data from geologic samples - known as the single silicate crystal approach - having higher fidelity than standard procedures. Preliminary data applying this method leads the team to an alternative hypothesis. Rather than recording a rotation of the entire solid Earth, the data reflect a geomagnetic field 565 million years ago that was in an unusual state: it was weak, and the poles reversed frequently. The team will test their hypothesis through a single silicate crystal paleomagnetic study of samples from three areas of southern Canada. Because the strength of the geomagnetic field is a principal factor defining shielding of the planet from the solar wind, this study will also help constrain the potential influence of energetic solar particles on the atmosphere and biosphere during this critical time in Earth history. The data collected will also be useful for testing if continental plate velocities were higher than uniformitarian assumptions, in the past. The work will support graduate students and undergraduates, who will acquire valuable skills though training in the classroom, field studies and in the laboratory. The suggestion that the entire solid Earth rotated by 90 degrees during Ediacaran to early Cambrian times (approximately 635-530 Ma), and that this sparked the early Cambrian explosion of life, is highly contentious. This is not a question of whether such an event, known as inertial interchange true polar wander (IITPW), is theoretically possible, but rather whether it occurred. Ultimately, the veracity of the event relies on the fidelity of paleomagnetic data. The PI team has recently examined this enigma using single silicate crystal paleomagnetic analysis, a method that allows the isolation of single-domain magnetic carriers that are the best field recorders, capable of preserving remanences on billion-year time scales. In their study of the Sept-Iles (approximately 565 Ma) intrusion (Canada), they have not found support for IITPW. Instead, they find evidence that the geomagnetic field was reversing during cooling of the intrusion. Preliminary analyses further suggest unusually low paleointensities. These observations provide the basis for an alterative hypothesis: the Ediacaran to early Cambrian geomagnetic field was unusually weak, and reversed frequently. The team will study three areas in southern Canada to test their hypothesis. This work will also broadly constrain the boundary conditions for biotic evolution during the key Ediacaran to early Cambrian interval, and will have implications for the core, mantle and surface environment. Specifically,the investigators hope to constrain i. whether the geodynamo was in an unusual state (perhaps associated with inner core growth), ii. if the magnetopause standoff distance was reduced, allowing greater penetration of energetic solar particles, and iii. if continental plate velocities were higher than uniformitarian assumptions. The work will support graduate students and undergraduates, who will acquire valuable skills though training in field studies in southern Canada and in the laboratory. They will combine field excursions, classroom studies and summer programs to give students a comprehensive research experience.

大约5.65亿年前，整个固体地球旋转了90度，这一事件引发了地球上生命的爆炸（当时最初出现的最初动物的门和阶级时）是地球科学中最具争议的假设之一。最终，这一想法的真实性取决于过去在古代岩石样品（古磁性学科的权限）中记录过去的地磁领域的程度。 PI已开发出一种从地质样品（称为单硅酸盐晶体方法）获得的古磁数据的方法，其保真度高于标准程序。应用此方法的初步数据使团队提出了替代假设。数据没有记录整个固体地球的旋转，而是反映了5.65亿年前的地磁场，处于异常状态：它很弱，而两极经常逆转。该小组将通过对加拿大南部三个地区的样品进行单次硅酸盐晶体古磁研究来检验他们的假设。由于地磁场的强度是定义行星免受太阳风的屏蔽的主要因素，因此本研究还将有助于限制在地球历史上这个关键时期，能量太阳颗粒对大气和生物圈的潜在影响。如果过去，收集的数据也可用于测试大陆板速度高于统一的假设。这项工作将支持研究生和本科生，他们将在课堂，野外研究和实验室中培训中获得有价值的技能。关于整个固体地球在Ediacaran期间旋转90度的建议，至寒武纪早期（约635-530 MA），这引发了早期寒武纪生命的早期爆炸，这是高度争议的。这不是一个问题，在理论上可能是可能的事件，即称为惯性互换的真实极地徘徊（IITPW），而是发生的。最终，事件的真实性取决于古磁数据的保真度。 PI团队最近使用单个硅酸盐晶体古磁分析检查了这种谜，这种方法允许隔离单域磁性载体，该磁载体是最佳的现场记录器，能够在数十亿年度尺度上保留remansence。在对SEPT-les（大约565 MA）入侵（加拿大）的研究中，他们尚未找到对IITPW的支持。取而代之的是，他们发现证据表明在侵入冷却过程中，地磁领域正在逆转。初步分析进一步表明了异常较低的质感。这些观察结果为换句假设提供了基础：Ediacaran到早期的寒武纪地磁场异常弱，并且经常逆转。该小组将研究加拿大南部的三个地区以检验其假设。这项工作还将广泛地限制关键Ediacaran期间生物进化的边界条件，并将其对核心，地幔和表面环境有影响。具体而言，调查人员希望限制i。 Geodynamo是否处于异常状态（可能与内部核心生长有关），ii。如果减少了磁笼式距离距离，从而使能量太阳颗粒的渗透更大，并且III。如果大陆板速度高于统一的假设。这项工作将支持研究生和本科生，他们将通过在加拿大南部和实验室的实地研究中获得有价值的技能。他们将结合现场游览，课堂研究和夏季计划，为学生提供全面的研究经验。