How soon after a planet's formation can animal life emerge? The answer to this question could influence how we search for life on other worlds, as well as the types of life we look for. Until recently, experts estimated that animals emerged on Earth around 555 million years ago, meaning that complex life can get kick-started pretty quickly, if the conditions are right.
But now, it's looking as though primitive animals on Earth emerged even earlier than we thought –- as much as 30 million years earlier.
An emerging thought in astrobiological circles is that the Universe is fairly "biophilic" — in other words, it's pretty friendly when it comes to the spawning and fostering of life. We now know that rocky planets litter our Galaxy in the trillions, but we're still not sure how easy it is for life to emerge and evolve on these planets. But if we can prove that microbes emerged very early in Earth's history, it's quite reasonable to assume that life can start quickly in other places as well.
Still, the emergence of microbial life is one thing. The step from prokaryotic and eukaryotic life to complex organisms may be quite another –- it might actually be a massively difficult evolutionary step. It's quite possible, for example, that many planets are "stuck" in the microbial stage. But new evidence suggests that that may not be the case -– at least, it wasn't on Earth.
This is an important question: If it's a relatively easy step for microbes to evolve into more complex organisms, it might also be relatively easy for intelligence to emerge as well.
Our planet formed 4.6 billion years ago, and rocks began to appear about a billion years later. Life emerged quickly thereafter, a mere 600 million years after the formation of rocks. And then, 3 billion years later (555 million years ago), animal life emerged. By all accounts, that's not a terribly long expanse of time in cosmological terms, an indication that the environmental conditions required for the development of complex life emerges fairly quickly after a planet's formation.
And now, a study from the University of Alberta's Ernesto Pecoits and Natalie Aubet reveals that we need to yet again push back our notions of when animal life is capable of emerging. Working in Uruguay, the team discovered the fossilized tracks of a tiny, slug-like animal living 585 million years ago in a silty sediment –- 30 million years earlier than any other animal remnant found to date.
The animal, called a bilaterian, was soft-bodied, and capable of manaeovering through the sediment of the shallow ocean floor. According to the researchers, the pattern of movement indicates that it was capable of moving and searching for food, possibly organic material in the sediment.
This is the first piece of evidence to support the theory that bilaterian life emerged during the Ediacaran period of Earth's history.
Of course, the rapid orgination of animal life on Earth doesn't imply that this is the case in other parts of the Universe. The conditions here may very well be special — unique in a way that we still need to understand. But the Pecoits and Aubet discovery is exciting, a potential glimpse into the workings of a Universe that's friendly to life.
Check out the entire study in Science: "Bilaterian Burrows and Grazing Behavior at >585 Million Years Ago".
Top image of bilaterian fossil courtesy dev.biologists. Inset image via Toronto Sun. Source: Stephen J. Mojzsis.