She thought they could be significantly but only recently became convinced they were fossilized proof of sponges that existed nearly a billion years ago.
It wasn’t until the past few years, when she saw studies that described similar structures in much younger rocks — from a time when sponges were known to exist — that Turner felt confident in publishing her results.
But scientists using a line of reasoning called the molecular clock — where they analyze the rate of genetic mutations to backdate when two species likely diverged — say that available evidence points to sponges emerging much earlier, around a billion years ago.
I’ve done a little fossil hunting in Utah and Wyoming, though most of the fossils I’ve dug up there are only about 50 million years old.