This is a bit of a trick question! While the Earth's mantle is the largest layer by volume and mass, it's not what contains 67% of *your* mass.

The answer is water.

Here's why:

* Human Composition: The human body is primarily composed of water (around 60% or more).

* Earth's Composition: While the Earth has a lot of water, it's a much smaller percentage of the planet's total mass than the mantle.

So, while the Earth's mantle is huge, it's not what makes up the majority of your body. It's the water you drink, the water in your cells, and the water that makes up your blood.