Short answers, pulled from the story.
Geophysics is a physical science concerned with the processes and properties of Earth and its surrounding space environment, studied using quantitative and observational methods. It covers Earth's shape, gravitational and magnetic fields, internal structure, tectonics, volcanism, oceans, atmosphere, cryosphere, ionosphere, and magnetosphere, as well as analogous processes on other planets.
Zhang Heng, described as a prolific inventor, built the first known seismoscope in 132 AD. The device dropped a bronze ball from the mouth of a dragon into one of eight surrounding toads to indicate the direction of a distant earthquake. It was 1571 years before the first European design for a seismoscope appeared, published by Jean de la Hautefeuille, and that design was never built.
Geomagnetic reversals occur when the polarity of Earth's magnetic field, generated by fluid motions in the liquid outer core, randomly flips. They occur at irregular intervals averaging 440,000 to a million years. A geomagnetic polarity time scale records 184 polarity intervals in the last 83 million years, with the most recent brief complete reversal, the Laschamp event, occurring 41,000 years ago.
Geophysics emerged as a separate discipline in the 19th century. The first known use of the word geophysics was in German, as Geophysik, by Julius Fröbel in 1834. Before that, geophysical phenomena such as Earth's magnetic field and earthquakes had been investigated since antiquity, but the science had no unified name.
Radioactive decay accounts for about 80 percent of Earth's internal heat. The main heat-producing isotopes are potassium-40, uranium-238, uranium-235, and thorium-232. This heat powers the geodynamo, which generates Earth's magnetic field, and drives mantle convection, which moves tectonic plates.
Seismologists found that S-waves, which require solid material to propagate, are absent in the outer core. Because liquids cannot support shear, this absence proved the outer core is liquid. The inner core is solid, held in that state by the immense pressure at Earth's center.