The first animal to appear on Earth was very likely the simple sea sponges. According to researchers at the world-famous Massachusetts Institute of Technology (MIT), sea sponges pre-date the Cambrian explosion, an evolutionary period that began around 540 million years ago, during which a large number of new animals appeared. The researchers confirm that sea sponges are the source of a curious molecule found in rocks that are 640 million years old.

One rare molecule in particular, 24-Isopropylcholesterol, or 24-IPC, has been found in rocks that are 640 million years old. It’s also known to be produced by sea sponges.

The researchers found that both sea sponge and algae species have the right number of copies of SMT to produce 24-IPC, and by analysing these genes and producing evolutionary trees based on the fossil record, they found that sea sponges were producing the molecule long before algae.

The scientists believe they reached this milestone around 640 million years ago – the same period in which the rocks containing 24-IPC were formed. This study provides strong evidence that sea sponges appeared on the Earth much earlier than any other animals.

The results have been published in the Proceedings of the National Academy of Sciences.