24-Isopropylcholestane

[3][4] In this transitional period at the start of the Phanerozoic, single-celled organisms evolved to produce many of the evolutionary lineages present on Earth today.

[5] Interpreting 24-isopropyl cholestane in ancient rocks as indicating the presence of sponges before this rapid diversification event alters the traditional understanding of the evolution of multicellular life and the coupling of biology to changes in end-Neoproterozoic climate.

However, there are several arguments against causally linking 24-isopropyl cholestane to sponges based on considerations of marine algae and the potential alteration of organic molecules over geologic time.

High abundances of 24-isopropyl cholestane are identified in the Precambrian rocks from the Hufq supergroup in Oman, suggesting the presence of sponges prior to the Cambrian explosion.

If correct, these results would give scientists much more confidence in interpreting elevated levels of 24-isopropyl cholestane in ancient rocks as reflecting the presence of sponges.

Climate change before the Cambrian explosion and the subsequent diversification of life are intricately intertwined with understanding the causes of Snowball Earth episodes,[11] the deposition of Banded Iron Formations,[12] and the second step in the rise of atmospheric oxygen.

Figure 1: 24-isopropyl cholestane (left) and 24-n-propyl cholestane (right), two organic molecules produced by sponges and marine algae relevant for studying the evolution of multicellular life in the Precambrian and Phanerozoic.