Although Tkalčić's work confirmed the core is solid, the shear waves were 2.5 percent slower than expected. From this Tkalčić concluded the core is softer than even the least rigid estimates produced in a longstanding debate on the stiffness of the core. He told IFLScience two explanations have been proposed, one involving melted pockets trapped within the core, the other reflecting the structure of iron crystals at the immense pressures the core experiences.
The core is known to be mostly iron and nickel, with some lighter elements, but Tkalčić says his work has yet to distinguish between the proposed impurities of sulfur, oxygen, and silicon.
Tkalčić hopes the measurements will improve models that “track the evolution of the inner core back in time.” He believes it will be possible to “estimate its age based on its characteristics and understand the point at which it started solidifying.”
Identifying the conditions under which the inner core formed, and therefore is likely to form on other worlds, has major implications for the quest for extraterrestrial life. “We know that the latent heat of solidification drives convection in the outer core,” Tkalčić told IFLScience.
Since this convection induces the Earth's magnetic field, without which life on Earth would probably not exist, we have reason to be very thankful for our planet's soft heart.