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Our understanding of the past behavior of the geomagnetic field arises from magnetic signals stored in geological materials, e.g., (volcanic) rocks. Bulk rock samples, however, often contain magnetic grains that differ in chemistry, size, and shape; some of them record the Earth's magnetic field well, others are unreliable. The presence of a small amount of adverse behaved magnetic grains in a sample may already obscure important information on the past state of the geomagnetic field. Recently it was shown that it is possible to determine magnetizations of individual grains in a sample by combining X-ray computed tomography and magnetic surface scanning measurements. Here we establish this new Micromagnetic Tomography (MMT) technique and make it suitable for use with different magnetic scanning techniques, and for both synthetic and natural samples. We acquired reliable magnetic directions by selecting subsets of grains in a synthetic sample, and we obtained rock-magnetic information of individual grains in a volcanic sample. This illustrates that MMT opens up entirely new venues of paleomagnetic and rock-magnetic research. MMT's unique ability to determine the magnetization of individual grains in a nondestructive way allows for a systematic analysis of how geological materials record and retain information on the past state of the Earth's magnetic field. Moreover, by interpreting only the contributions of known magnetically well-behaved grains in a sample, MMT has the potential to unlock paleomagnetic information from even the most complex, crucial, or valuable recorders that current methods are unable to recover.

For archeomagnetic dating, high-quality directional and intensity paleosecular variation curves are needed. The Azores Archipelago in the mid-Atlantic Ocean provides a wealth of volcanic products erupted during the Holocene, making it an ideal location to (1) gather paleomagnetic data from well dated lava flows and (2) construct a paleosecular variation (PSV) curve that enables paleomagnetic dating of volcanic products with unknown age. Here, we present new full-vector paleomagnetic data from Pico Island, and combine the new data with existing data from neighboring islands to construct a new full-vector PSV curve for the Azores Archipelago. An extensive rock-magnetic study underpins the quality of our paleomagnetic carriers. From Pico Island, we obtained 21 new mean site directions; and 15 paleointensity estimates with the multimethod paleointensity approach from 12 sites, the age was known for 14 and 10 sites, respectively. By bootstrapping the non-Gaussian uncertainty estimates of the radiocarbon age calibrations and the confidence intervals associated with the direction and paleointensity estimates, we produce the first full-vector PSV curve with confidence intervals for the Azores covering the past 2 kyr. The PSV curve reveals a period of low inclination between ∼900 and 1560 AD, with minimum values of 32°. The potential of our new full-vector PSV curve is demonstrated by successfully dating five lava flows from Pico Island.

Paleointensity.org is an online, open source, application to analyze paleointensity data produced by the most common paleointensity techniques. Our application currently supports four different methods: thermal Thellier (all variations), microwave Thellier, pseudo-Thellier, and the multispecimen protocol. Data can be imported using a variety of input file formats such as ThellierTool files, the generic PmagPy file format, and a number of lab-specific formats. The data for the individual paleointensity methods are visualized by the relevant graphs and parameters, which are updated dynamically while interpreting the data. Beyond manual interpretation, Paleointensity.org features an autointerpreter for specimen level Thellier-type data. Interpretations and data can be exported to csv and MagIC files. Moreover, it is possible to export the local storage containing all data, saved interpretations, and settings. This file can be shared among researchers or attached to a paper as supporting information. Because of its many features and ease of use, Paleointensity.org is a major step forward in enhancing an open paleomagnetic community in which data can be shared, checked, and reused in line with the findable, accessible, interoperable, and reusable data principles.

Our understanding of the behavior of the geomagnetic field arises from magnetic signals stored in geological materials, e.g. lavas. Almost all experiments to determine the past state of the Earth’s magnetic field use bulk samples (typically 1 - 10 cc) and measure their magnetic moment after series of laboratory treatments. Lavas, however, consist of mixtures of different iron-oxide grains that vary in size, shape, and chemistry. Some of these grains are good recorders of the Earth’s magnetic field; others are not. Only a small amount of adverse behaved magnetic grains in a sample already hampers all classical experiments to obtain paleointensities; success rates as low as 10-20% are common, i.e. for 80-90% of all lavas vital information on paleointensities is lost before it can be uncovered. Recently, we showed that it is possible to determine the magnetization of individual grains inside a synthetic sample using a new technique: Micromagnetic Tomography. The individual magnetizations of grains are determined by inverting scanning magnetometry data from the surface on the sample onto the known locations, sizes and shapes of the magnetic grains that are obtained from a microCT scan of the sample. The synthetic sample used for our proof-of-concept, however, was optimized for success: the dispersion of magnetic markers was low, and the magnetite grains had a well-defined grain size range. Furthermore, the scanning SQUID microscope used requires the sample to be at 4 K, below the Verweij transition of the magnetite grains. Here we present the first Micromagnetic Tomography results from natural samples. We used two magnetic scanning techniques that operate at room temperature, a Magnetic Tunneling Junction set-up and a Quantum Diamond Magnetometer, to acquire the magnetic surface scans from a Hawaiian lava and calculated magnetic moments of individual grains present. We show that it is possible to acquire rock magnetic information as function of grain size from these natural samples and reveal the first results of interpreting a paleomagnetic direction from selected subsets of grains in our samples. These are the first steps towards deriving rock magnetic and paleomagnetic information from subsets of known good recorders inside lava samples, a technique that will revolutionize our field of research.

Obtaining reliable information from even the most challenging paleomagnetic recorders, such as the oldest igneous rocks and meteorites, is paramount to open new windows into Earth's history. Currently, such information is acquired by simultaneously sensing millions of particles in small samples or single crystals using superconducting quantum interference device magnetometers. The obtained rock-magnetic signal is a statistical ensemble of grains potentially differing in reliability as paleomagnetic recorder due to variations in physical dimensions, chemistry, and magnetic behavior. Here we go beyond bulk magnetic measurements and combine computed tomography and scanning magnetometry to uniquely invert for the magnetic moments of individual grains. This enables us to select and consider contributions of subsets of grains as a function of particle-specific selection criteria and avoid contributions that arise from particles that are altered or contain unreliable magnetic carriers. This new, nondestructive, method unlocks information from complex paleomagnetic recorders that until now goes obscured.

The Dutch Inspectorate for Education established that the quality of elementary students’ writing is below the desired level, and that the teaching of writing must be improved. The aim of this PhD research was therefore to improve writing education in upper elementary grades by developing an effective teaching program for writing, including professional development for teachers, and tools for the assessment of writing. Building on the findings of previous research, we developed and tested Tekster [Texter], a strategy-focused comprehensive program for teaching writing in grade 4 to 6. Tekster combines several evidence-based practices, such as strategy instruction, goal setting, text structure instruction and observational learning into one general approach to address both the focus and mode of writing instruction. Tekster was developed in close collaboration with elementary teachers. The effectiveness of Tekster was tested in two large-scale intervention studies with 144 teachers and 2766 students from 52 schools. Students’ writing performance was assessed with multiple tasks in multiple genres in order to draw inferences about students’ underlying writing proficiency. The quality of their texts was rated by multiple raters using a benchmark rating scale. To ensure that the intervention was implemented with fidelity, teachers were provided with a manual and training. In the first study students’ writing performance improved significantly after following the Tekster program, with an effect size of 0.40, while generalizing over students, teachers, and tasks. The improvement was established in all grades and maintained two months after the intervention. In the second study, in which we added a professional development program, the effect size was even higher, i.e., 0.55. This study specifically showed that teachers became more positive and felt more efficacious about the teaching of writing after working with the program. They were highly satisfied with Tekster and the professional development activities. Moreover, it was shown that teachers were able to transfer their newly acquired knowledge and skills to colleagues. In two subsequent studies we specifically investigated the effectiveness of the writing strategy. This strategy divides the writing process into a prewriting, writing, and post-writing phase. We found that explicitly teaching students a writing strategy enhanced their metacognitive knowledge about writing and promoted the use of prewriting activities, which improved the quality of their texts. Further, we examined whether teachers are able to adequately provide feedback to texts of varying quality. Results show that the type and amount of feedback depends more on the style of the teacher than on the actual performance of the student, and that additional training for teachers is necessary to optimize the effectiveness of feedback. Therefore feedback formed a substantial part of the professional development program of Tekster. To summarize, this PhD research demonstrates that a comprehensive writing program, such as Tekster, is a promising approach to improve writing education in elementary grades. The program appeared to be effective for students and teachers. All in all, this research provides valuable clues on how the gap between research and classroom practice can be bridged to improve writing education.