The term “sky burial” can refer to several very different burial traditions, both ancient (like the Sky Burial rituals practiced by Tibetan Buddhists or the Zoroastrians) and modern (such as scattering ashes at high altitude).
The Tibetan Buddhist practice a form of “sky burial” in which the deceased is ritually dissected and “offered to nature” on a mountaintop. The remains are exposed to the elements and animals, such as birds of prey, thus becoming a part of the circle of life.
The Zoroastrian tradition utilizes a “Tower of Silence” for their Sky Burials. The deceased is laid to rest on the top of the tower – exposed to elements and birds of prey.
Both the Tibetan Buddhist and Zoroastrian traditions are fading – replaced by different traditions, or even banned in some places.
The more modern definition of “sky burial” is the scattering of cremated remains (cremains) for an airplane – either by sky divers or at a very high altitude. There is also a company that will send your ashes into space.