NO OTHER BONE ON EARTH LOOKS LIKE THIS
The bone of the Starchild Skull is uniformly only 1/3 as thick as normal human bone, and weighs about 1/3 as much. It is made of the same basic components as human bone, but the levels of some elements, most notably carbon and oxygen, are higher than in a normal human, and when polished the bone looks yellow and opaque compared to human bone, which is whiter and more translucent. The bone is so strong that it is difficult to cut with a standard tungsten carbide rotary bone saw. One lab team resorted to using a diamond coated blade to cut samples for testing. There is no known condition that can make bone thinner, lighter, and stronger.
The outside surface of human bone is covered in little pits called "Lacunae", which are essential to healthy bone growth. They help move waste out of and nutrients into the bone, and they are resistant to hypoxia (lack of oxygen). These are almost entirely absent in the Starchild Skull, which begs the question, how did it have more oxygen in it's bone and yet lacks one of the main elements that keeps bone oxygenated?
Some skeptics try to dismiss the thin bone of the Starchild Skull as being a result of post mortem shrinkage, and bone can become thinner after death, but the comparisons shown here are between the 900 year old Starchild bone, and 900 year old human bone from a skull found in the same location as the Starchild. They have been exposed to identical conditions ever since they both died, so we are absolutely comparing apples to apples. There is no condition known to man that can cause human bone to become thinner, lighter, and at the same time stronger.
The image at the bottom right shows a Polished section of human bone, compared to a polished section of Starchild Skull bone, both to scale and prepared using the same method but with very different results.