If Earth’s history is an epic book, we have to get by without the first few chapters.
The very beginning of life as we know it is a mystery. We know that ancient organisms were evolving. And we even have rocks that were formed in the earliest days.
But they left us absolutely no physical evidence of what happened in the beginning, the most profound mystery of Earth.
What if the truth about the earliest animals has been hiding in plain sight?
The missing chapters: What scientists need to know about complex life
Scientists experience the utmost frustration not knowing how complex life began.
They imagine there was some fundamental spark that set off the birth of early life forms. But there’s never been any way to tell.
“Darwin’s Dilemma” encompasses this massive, 150 million-year gap in our fossil record.
For this entire period, we know that life must have existed. But no amount of searching has been able to uncover the clues we need in the rocks from that time.
There’s a logical reason why we can’t find fossils in the rocks (although this doesn’t make the not knowing any easier to bear).
It’s because early life forms didn’t have hard parts like shells or bones. This made fossilization nearly impossible under normal conditions.
This has never stopped researchers from searching for the answers. And it may have finally paid off, according to the study, “Scientists just solved a 160-million-year fossil mystery: ‘I’ve never seen anything like it’,” published by Virginia Tech.
Against the odds: A time capsule unearthed in China
The Yangtze River Gorge is 70 million years old. A massive tectonic rising buckled the crust of the Earth, creating a dramatic terrain of limestone cliffs and shale valleys.
This process exposed highly preserved, low-oxygen sedimentary strata.
While the geography sounds dry, it created a perfect time capsule of Earth’s earliest soft-bodied life.
The field research that went into finding microscopic clues in the ancient rock layers was painstaking. But researchers were motivated more than usual.
They hunted for exceptional preservation environments above all.
These are sites where catastrophic underwater mudslides choked out oxygen. Crucially, soft tissues were locked away before they could rot.
In 2019, the perseverance paid off, and researchers brought an incredibly rare, pristine imprint in the sediment to light.
What animal’s body managed to survive that ancient mudslide to be touched by human eyes millions of years later?
The secret in the stone: A soft sign from the seas
A sea sponge hardly seems mysterious. But this fossil discovery has fascinating implications.
The sponge in the Yangtze Gorge stone is an incredible 550 million years old. And it’s helping to solve a long-standing evolutionary mystery.
Sea sponges have no brain and no gut. Scientists estimate that they originated around 700 million years ago.
Yet fossil evidence only dates back about 540 million years.
We’re left with a puzzling 160 million-year gap in the record, because sponges seemed to “vanish” during a time that many other fossils, like dinosaurs, survived.
Out of the mists of “the lost years”
Virginia Tech geobiologist Shuhai Xiao and his collaborators describe a sea sponge fossil that falls squarely within this missing interval.
The team has an explanation for the gap: the first sponges may not have had mineral skeletons, making them far less likely to fossilize.
This idea helps resolve a long-standing paradox in evolutionary science. It adds an important detail to the evolutionary history of one of Earth’s earliest animals.
The researchers found that sponges became more mineralized through evolution. The further back, the more organic and less mineral-based these structures appeared.
Finding a soft-bodied sponge means our book of early life is being rewritten.
This opens up the thrilling possibility that other “invisible” ancestors are waiting to be found in the mud of the ancient past. We could even look to space for more fossils to learn from.