Final answer:
Scientists determined that Earth's inner core is solid based on seismological data interpreted by Inge Lehmann, who noticed the absence of shear waves and the presence of compression waves, pointing to a liquid outer and solid inner core. This, alongside studies on Earth's density and the composition of meteorites, confirmed the solid state of the inner core.
Step-by-step explanation:
D_anish geophysicist Inge Lehmann was instrumental in using seismological evidence to prove that Earth has a solid inner core. This discovery h_inged on the observation that shear waves, which cannot pass through liquid, were absent in the core, while compression waves did pass through, indicating a liquid outer core and a solid inner core. Moreover, the fact that Earth has not cooled down to a solid state despite being over 4.5 billion years old implies that radioactive decay within the core is generating heat, preventing such cooling.
The Earth's core is highly dense, indicated by calculations based on the planet's rotation and is believed to be composed mostly of iron, with some nickel, and other elements like sulfur. Researchers have also used seismic wave analysis to confirm the liquid state of the outer core and the solidity of the inner core. Samples from the upper mantle that are occasionally ejected from volcanoes allow for detailed analysis, supporting the understandings of the Earth's composition and structure.
These findings from seismological data and geological study have helped map out the interior structure of Earth, with a solid inner core about 2400 kilometers in diameter and a liquid outer core that is larger than the planet Mercury. The study of seismic waves not only helped confirm the phases of the core but also allowed scientists to estimate the temperature and composition of these deep Earth layers.