Final answer:
Scientists discovered Earth's outer core is liquid because shear waves from earthquakes do not pass through it, while compression waves do. Inge Lehmann interpreted seismic data to confirm this structure. The core's heat is maintained by the radioactive decay of elements.
Step-by-step explanation:
The question relates to how scientists discovered that Earth's outer core is liquid. Inge Lehmann played a pivotal role in interpreting seismological data from earthquakes. It was observed that shear waves, which cannot travel through liquid, do not transmit through the Earth's core, unlike compression waves, which do. This was key evidence indicating that the outer core was liquid.
Since shear or transverse waves are not transmitted through the Earth's outer core, but longitudinal waves pass through, it indicated differing properties consistent with a liquid outer core and a solid inner core. The Earth's core was found to consist of a liquid outer core surrounding a solid inner core, made of materials like iron and nickel. The composition and presence of these elements also led to the creation of Earth's magnetic field.
The substantial heat of the Earth's interior, despite the expectation of cooling over 4.5 billion years, is maintained by the radioactive decay of primordial elements. The density of the mantle rock increases with depth and occasionally is studied when ejected from volcanoes, bearing detailed chemistry for analysis.