Ancient Sponges may Represent Earth’s Earliest Animal Life, New Research Suggests
Evidence suggests that ancient sponges may be among the first animals to have evolved on Earth, appearing substantially earlier than most other multicellular organisms. A recent study, focusing on a specific organic compound, strengthens this hypothesis.
Researchers identified a geological stable sterol form, a 30-carbon (C30) sterol – a component of steroid groups including cholesterol – within ancient rock formations. This sterol is typically found in the cell membranes of complex organisms. The team connected this specific sterol to Demosponges, a class of sea sponges, indicating the “chemical fossil” represents traces of early animal life.
“We did not know exactly what this organism was like at that time, but they must have lived in the ocean, soft body, and we suspect they did not have a silica frame,” explained roger Summons, professor of geobiology at MIT’s Department of Earth, Atmospheric and Planetary Sciences, as quoted by IFL Science.
Sponges, despite their simple appearance, are classified as animals. They are composed of diverse eukaryotic cells performing specialized functions,lack cell walls,and exhibit behaviors like eating,reproduction,and responding to their environment. However, they are relatively simple animals, lacking organs, tissues, and complex systems like nervous systems or circulatory systems. Essentially, they are aggregations of animal cells.
The emergence of these early sponges predates the Cambrian explosion, a period of rapid diversification of complex life forms marked by a sudden appearance of many animal groups in the fossil record. Prior to this, life primarily consisted of simpler structures and single-celled organisms.
Initial findings in 2009 suggested C30 sterols could indicate early animal life, but alternative theories proposed the sterols might originate from other organisms or geological processes.
This new research bolsters the original claim. By analyzing drill cores and rock outcrops from Oman,western India,and Siberia,the team found evidence linking the sterols strongly to Demosponges.
“You are not eukaryotes if you don’t have a comparable sterol or lipid membrane,” Summons stated.
further, the team synthesized C30 sterols in a laboratory setting, demonstrating their production using enzymes encoded by Demosponge genes. This combined evidence – analysis of the rock samples, characteristics of modern sponges, and laboratory synthesis – firmly supports the conclusion that the 635-million-year-old rocks contain evidence of ancient animal life.
“This is a combination of what is in the stone, what is in the sponge, and what you can make in the chemical laboratory. There are three lines of evidence that support and mutually reinforce each other, showing that this sponge is among the earliest animals on earth,” Summons concluded.
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