The inner core of the Earth is the most dense layer.

Here's why:

* Composition: The inner core is primarily made of iron with a small percentage of nickel.

* Pressure: The immense pressure from the weight of all the layers above it squeezes the atoms of iron together, making it incredibly dense.

* Density: The inner core has a density of about 13 g/cm³, which is roughly twice as dense as lead!

While the mantle is much larger than the core, it's composed of mostly silicate minerals, making it less dense than the iron-rich inner core.