Red ochre was a regularly used substance in Paleolithic sites. It is a naturally found mixture of sand and hematite.
Red ochre is a common substance throughout the world, which may be why it was thought of as the earth's blood.
Red ochre was used in conjunction with death and caves (womb), suggesting a combination that meant rebirth. It was common for bones left over after excarnation to be placed deep in a cave or in some artificial cavern and covered with red ochre in order to aid in the process of rebirth.