Short Answer 
Cremation is a complex process where certain parts of the body, like the belly button, do not turn to ash. Historically significant across various cultures, it has evolved from methods like open-air pyres to modern crematoriums. Additionally, it holds religious significance in traditions such as Hinduism and Jainism, though its practice has fluctuated over time.
Step 1: Understanding the Physical Aspects of Cremation
Unlike what some may believe, the deceased’s belly button remains intact and does not turn to ash during the cremation process. It retains its original shape, as it did on the human body. This peculiar aspect highlights the complexity of human remains and how certain parts react differently during cremation.
Step 2: Historical Background of Cremation
Cremation has a long history, utilized as a ritual in various cultures across the globe. It can be carried out in different forms, such as:
- Open-air pyre: An ancient method still practiced in countries like India and Nepal.
- Cremation at a crematorium: This modern method commonly uses a closed furnace (cremator).
- Historical roots: Documented in India around 1900 BCE, marking the shift from the Indus Valley Civilisation to the Vedic civilization.
Step 3: Cultural and Religious Significance
Cremation is more than just a method of disposing of human remains; it holds significance in various religions. For instance:
- Hinduism and Jainism: Both religions prescribe cremation as a sacred ritual for the deceased.
- Decline in Europe: The practice waned with the rise of Christianity, although it had already faced declining popularity before that.
- Modern revival: Since the 19th century, cremation has been re-established in many parts of the world.