The nature of the Ediacaran to early Cambrian geomagnetic field

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大爆发（当时大多数现存的动物门类和类别首次出现），这是地球科学中最具争议的假设之一。最终，这种观点的真实性取决于古代岩石样本（古地磁学科的范围）对过去地磁场的记录有多好。pi开发了一种从地质样品中获取古地磁数据的方法——被称为单硅酸盐晶体方法——比标准方法具有更高的保真度。应用这种方法的初步数据使研究小组得出了另一种假设。这些数据并没有记录整个固体地球的旋转，而是反映了5.65亿年前处于一种不寻常状态的地磁场：它很弱，两极经常反转。研究小组将通过对加拿大南部三个地区的单一硅酸盐晶体古地磁样本进行研究，来验证他们的假设。由于地磁场的强度是确定地球屏蔽太阳风的主要因素，因此这项研究还将有助于限制高能太阳粒子在地球历史上这一关键时期对大气和生物圈的潜在影响。收集到的数据也将有助于检验过去大陆板块速度是否高于均变说假设。这项工作将支持研究生和本科生，他们将通过课堂、实地研究和实验室的培训获得宝贵的技能。在埃迪卡拉纪到寒武纪早期（大约635-530 Ma），整个固体地球旋转了90度，这引发了寒武纪早期的生命大爆发，这一说法极具争议。这不是一个被称为惯性交换真极漂移（IITPW）的事件在理论上是否可能的问题，而是它是否发生过的问题。最终，事件的真实性取决于古地磁数据的保真度。PI团队最近使用单硅酸盐晶体古磁学分析来研究这个谜，这种方法可以隔离单畴磁载流子，这是最好的现场记录器，能够在数十亿年的时间尺度上保存残留物。在他们对Sept-Iles（大约565 Ma）入侵（加拿大）的研究中，他们没有找到支持IITPW的证据。相反，他们发现有证据表明，在侵入物冷却期间，地磁场发生了逆转。初步分析进一步表明古强度异常低。这些观测结果为另一种假设提供了基础：埃迪卡拉纪到寒武纪早期的地磁场异常微弱，并且频繁反转。该团队将研究加拿大南部的三个地区来验证他们的假设。这项工作还将广泛地约束埃迪卡拉纪至早寒武世关键时期生物进化的边界条件，并将对地核、地幔和地表环境产生影响。具体来说，研究人员希望限制1 .地球发电机是否处于一种不寻常的状态（可能与内核生长有关）；如果磁层顶距离减小，允许高能太阳粒子更大的穿透；如果大陆板块速度高于均变说假设。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培训获得宝贵的技能。他们将结合实地考察，课堂研究和暑期课程，给学生一个全面的研究经验。

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.