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2h ago

Rare C31 Chemical Fossils Bolster Case That Sponges Were Earth’s Earliest Animals

Peer-reviewed analyses link Ediacaran steranes to demosponges through converging geochemical tests.

Some of the first animals on Earth were likely ancestors of the modern sea sponge, according to MIT geochemists who unearthed new evidence in very old rocks.
Colorful sea sponges line the ocean floor. (© denissimonov - stock.adobe.com)
A rare chemical indicator suggests sponges may have arrived as the first animals on Earth.
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Overview

  • An MIT-led PNAS study reports abundant C31 alongside C30 steranes in rocks older than 541 million years, strengthening a demosponge origin for the signals.
  • Drill cores and outcrops from Oman, western India, and Siberia yielded the rare biomarkers in Ediacaran-age sediments.
  • Analyses of living demosponges identified matching C31 sterols, tying modern biochemistry to the ancient sterane signatures.
  • Laboratory synthesis of eight C31 sterols followed by simulated fossilization showed only two yield the exact rock products, arguing against nonbiological formation.
  • The results reinforce a 2009 sponge interpretation while leaving precise timing and morphology unresolved, and the team plans broader global sampling to refine the record.