Japanese scientists believe they have established the identity of a "missing element" within the Earth's core.
They have been searching for the element for decades, believing it makes up a significant proportion of our planet's centre, after iron and nickel.
Now by recreating the high temperatures and pressures found in the deep interior, experiments suggest the most likely candidate is silicon.
The discovery could help us to better understand how our world formed.
The innermost part of our Earth is thought to be a solid ball with a radius of about 1,200km.
It is far too deep to investigate directly, so instead scientists study how seismic waves pass through this region to tell them something of its make-up.
It is mainly composed of iron, which makes up an estimated 85% of its weight, and nickel, which accounts for about 10% of the core.
Add this together though and around 5% is unaccounted for.
To investigate, Eiji Ohtani and his team created alloys of iron and nickel and mixed them with silicon.
They then subjected them to the immense pressures and temperatures that exist in the inner core.
They discovered that this mixture matched what was seen in the Earth's interior with seismic data.