Steptoean positive carbon isotope excursion
The Steptoean Positive Carbon Isotope Excursion (SPICE) was a geological event which occurred about 500 million years ago at the end of the Cambrian Period. The SPICE event was a sudden reversal of the anoxia (lack of oxygen) that had steadily spread throughout the oceans during the Cambrian which also affected the atmosphere. After the SPICE event, oxygen levels recovered and levels in the atmosphere may have risen as high as 30%, higher than the 21% of the atmosphere that prevails today. The sudden increase in oxygen led to an explosion of life across the globe.