Short answers, pulled from the story.
Earth's outer core is composed mostly of iron and nickel, with light elements mixed in to account for its lower density. By weight, estimates include iron plus 0 to 0.26 percent hydrogen, 0.2 percent carbon, 0.8 to 5.3 percent oxygen, 0 to 4.0 percent silicon, 1.7 percent sulfur, and about 5 percent nickel.
Earth's outer core is about 2,260 kilometres thick. It begins roughly 2,889 kilometres beneath the surface at the core-mantle boundary and ends 5,150 kilometres down at the inner core boundary.
Earth's outer core stays liquid because there is not enough pressure to keep it solid, even though it has a composition similar to the solid inner core. Seismology supports this, since seismic shear-waves are not transmitted through the outer core, and shear-waves cannot pass through fluids.
Eddy currents in the nickel-iron fluid of Earth's outer core are, under dynamo theory, the principal source of Earth's magnetic field. The field is driven by thermal and chemical convection, with the average field strength inside the outer core estimated at 2.5 millitesla, fifty times stronger than at the surface.
Earth's outer core is estimated at about 3,000 to 4,500 kelvin in its outer region and 4,000 to 8,000 kelvin near the inner core. This high temperature makes the outer core a low-viscosity fluid that convects turbulently.
The new core paradox arises from claims that iron's thermal conductivity at core temperatures and pressures is much higher than previously thought, implying core cooling was largely by conduction rather than convection. This would limit thermal convection's ability to drive the geodynamo, raising questions about how Earth's magnetic field was sustained before the inner core formed.