The Earth has its own magnetic field (the geomagnetic field), which is confined by the action of the solar wind into a volume called the magnetosphere (see Chapter 5.03). This field is not steady, but varies with time due partly to the interaction with the solar wind, but more importantly by its own physical processes. Direct observation of such changes has been carried out only in the last few centuries, but with indirect measurements we can understand the field behavior millions of years back in time. In this extended time frame, there is evidence that the polarity of the magnetic field reversed frequently, and that the magnetic dipole axis in very ancient times was significantly displaced from the present rotational axis (the North and South geographic Poles). It is of considerable interest how such knowledge was acquired over several centuries. We will take a brief tour of the historical events that provided important steps in formulating our understanding of the geomagnetic field. In doing so, we have to rely solely on the written records, which is the reason why only the European and Chinese histories are referred. There are many works on this topic; among them, the important ones are Mitchell (1932–46), Harradon (1943–45), Needham (1962), and Yamamoto (2003). The English translations of Chinese literature below were taken from Needham (1962). Chinese sentences given together with English were taken from the Japanese translation of this book (Hashimoto et al., 1977). When we talk about the earliest recognition of the magnetism of the Earth, we should be careful to discriminate two separate issues; that is, the attractive force exerted by a magnet on iron, and the north- (or south-) seeking property of the magnet. The former can be taken as the forerunner to the science of magnetism, while the latter is the basis for appreciation of the magnetic field associated with the Earth. Our main interest is in the geomagnetic field, but it is necessary to look into magnets first.

Mineral physics involves the application of physics and chemistry techniques in order to understand and predict the fundamental behavior of Earth materials (e.g., Kieffer and Navrotsky, 1985), and hence provide solutions to large-scale problems in Earth and planetary sciences. Mineral physics, therefore, is relevant to all aspects of solid Earth sciences, from surface processes and environmental geochemistry to the deep Earth and the nature of the core. In this volume, however, we focus only on the geophysical applications of mineral physics (see also Ahrens (1995), Hemley (1998), and Poirier (2000)). These applications, however, are not just be constrained to understanding structure the Earth (see Volume 1) and its evolution (see Volume 9), but also will play a vital role in our understanding of the dynamics and evolution of other planets in our solar system (see Volume 10 and Oganov et al. (2005)). As a discipline, mineral physics as such has only been recognized for some 30 years or so, but in fact it can trace its origins back to the very foundations of solid Earth geophysics itself. Thus, for example, the work of Oldham (1906) and Gutenberg (1913), that defined the seismological characteristics of the core, led to the inference on the basis of materials physics that the outer core is liquid because of its inability to support the promulgation of shear waves. A landmark paper in the history of the application of mineral physics to the understanding of the solid Earth is the Density of the Earth by Williamson and Adams (1923). Here the elastic constants of various rock types were used to interpret the density profile as a function of depth within the Earth that had been inferred from seismic and gravitational data. Their work was marked by taking into account the gravitationally induced compression of material at depth within the Earth, which is described by the Williamson–Adams relation that explicitly links geophysical observables (g(r), the acceleration due to gravity as a function of radius, r, and the longitudinal and shear seismic wave velocities Vp and Vs).

In the ten years that have passed since the publication of the first edition of this textbook exciting advances have taken place in every discipline of geophysics. Computer-based improvements in technology have led the way, allowing more sophistication in the acquisition and processing of geophysical data. Advances in mass spectrometry have made it possible to analyze minute samples of matter in exquisite detail and have contributed to an improved understanding of the origin of our planet and the evolution of the solar system. Space research has led to better

Первое издание энциклопедии по геофизике земли было издано в 1989 издательской компанией Вана Ностранда Реинхолда. Более двадцати лет спустя, это новое издание, отредактированное профессором Харшом К. Гупта, представляет полностью пересмотренную и расширенную работу. Энциклопедия объединяет более 200 статей, охватывающих уже установленные и новые концепции геофизики из различных разделов науки, таких как геодезия, геомагнетизм, сейсмология, глубинные земные процессы, тектоника плит, вычислительные методы, и т.д. в систематическом и последовательном формате. Это авторитетный источник информации благодаря вкладу редакторов и авторов со всего света, предназначенный для нынешних и будущих поколений профессионалов.

Книга представляет собой систематическое изложение основ палеомагнитологии, ее методов и приложений к геологии и геофизике.

Рассматриваются физические и геофизические явления, лежащие в основе палеомагнитологни, описываются современные методы и техника палеомагнитных исследований, излагаются результаты обобщения мировых палеомагнитных данных. Описывается морфология геомагнитных инверсий и палеовековых вариаций, рассматривается их ритмика в связи с процессами тектогенеза. Приводится и обосновывается магнитостратиграфическая шкала фанерозоя, анализируется проблема мировой палеомагнитной шкалы, рассматриваются принципы ее построения.

Географические полюса нашей планеты располагаются в Арктике и Антарктиде. А куда мы в конце концов придём, если будем идти по компасу точно на север? На северный географический полюс? Нет, магнитный северный полюс не совпадает с географическим. И в разные годы стрелка компаса может привести нас в разные места: магнитные полюса, в отличие от географических, не стоят на месте! В брошюре рассказывается о магнитном поле Земли, об истории изучения магнитных полюсов, а также об истории перемещения полюсов и нынешнем их движении. Текст брошюры подготовлен по материалам лекции, прочитанной автором 5 октября 2002 года на Малом мехмате для школьников 7—8 классов. Брошюра рассчитана на широкий круг читателей: школьников, студентов, учителей.