815-Million-Year-Old "Time Capsule" Reveals Atmosphere Breathed By Earth's Very First Animals

Ancient crystals reveal that Earth's atmosphere was suitable for animals as far back as 815 million years ago, at least. koTRA/Shutterstock

Around 600 million years ago, the planet’s multicellular lifeforms began to emerge and diversify. Known as “eukaryotes,” these initial forms would evolve into all the plants and animals we see around the world today.

Although they first appeared perhaps as early as 2.7 billion years ago, this particular explosive evolutionary period irrevocably changed the story of life on Earth – and many think that the rise in atmospheric oxygen may have been a driving factor. Writing in the journal Geology, an international team of researchers have described a discovery that could rewrite all of this.

Cracking open some 815-million-year-old halite (rock salt) and analyzing the gases inside, they found a perfectly preserved record of Earth’s ancient atmosphere. Previously, atmospheric compositions could only have been determined indirectly, but this halite proved to buck this trend.

“With this study, the oxygen in the air that allowed the earliest animals to breathe has been measured directly for the first time,” Professor John Parnell, the chair in geology and petroleum geology at the University of Aberdeen and co-author of the study, said in a statement. “We measured the oxygen at 10.3 to 13.4 percent of the atmosphere, which would have been enough for animals to flourish. In comparison, the oxygen content of modern Earth's atmosphere is 20.9 percent.”

As it turns out, this salty time capsule revealed that the atmosphere back then contained enough oxygen to sustain complex life, around 215 million years before the fossil record documents the presence of any such animals. Remarkably, this means that the emergence of complex life on Earth was possible as far back as 815 million years ago.

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This is the type of algae-rich sludge that first converted the planet’s atmosphere into an oxygen-rich one. Sakhorn/Shutterstock

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