Life has made a home on Earth for about 4 billion years. That’s a significant portion of the 13.77 billion year history of the universe. Presumably, if life had originated here, it could have appeared anywhere. And for sufficiently broad definitions of life, it might even be possible for life to have appeared just seconds after the event Big bang.
To explore the origin of life, we must first define it. There are over 200 published definitions of the term, proving just how difficult this concept is to grapple with. For example, are viruses alive? They replicate but need a host to do so. What about prions, the pathogenic protein structures? Debates continue to swirl about the boundary between life and non-life. But for our purposes we can use an extremely broad but very useful definition: life is anything that is subject to Darwinian evolution.
This definition is useful because we will be exploring the origins of life itself, which by definition will blur the lines between life and non-life. At some point, deep in the past, Soil was not alive. Then it was like this. This means that there was a transition period that will obviously push the boundaries of any definition you can muster. And as we dig deeper into the past and explore other possible options for life, we want to keep our definition broad, especially as we explore the more extreme and exotic corners of the world. universe.
Related: Life may have developed before the Earth formed
With this definition in hand, life on Earth emerged at least 3.7 billion years ago. By then, microscopic organisms were already advanced enough to leave traces of their activities that persist to this day. Those organisms were much like modern ones: they used DNA to store information, RNA to convert that information into proteins, and the proteins to interact with the environment and make copies of the DNA. This three-way combination allows these batches of chemicals to experience Darwinian evolution.
But those microbes didn’t just fall out of the sky; they came from somewhere. And if life is something that evolves, then a simpler version of life had to have existed even earlier in Earth’s past. Some theories speculate that the first self-replicating molecules, and thus the simplest possible form of life on Earth, could have emerged once the oceans cooled, well over four billion years ago.
And the Earth might not have been alone – Mars And Venus had similar circumstances at the time, so if life happened here, it may have happened there too.
The first life among the stars
But the Sun was not the first star in which it ignited merger; it is a product of a long line of previous generations of stars. Life as we know it requires a few key elements: hydrogen, oxygen, carbon, nitrogen and phosphorus. With the exception of hydrogen, which appeared in the first few minutes after the Big Bang, all of these elements are created in the hearts of stars during their life cycle. So as long as you have at least one or two generations of stars that live and die, thereby spreading their elements to the wider environment, universeyou can see Earth-like life appearing in the universe.
This pushes the clock back to more than 13 billion years ago for the possible first appearance of life. This era in the history of the universe is known as the cosmic dawn, when the first stars came into existence. Astronomers don’t know exactly when this transformative era took place, but it was sometime within a few hundred million years after the Big Bang. As soon as those stars appeared, they could have started creating the necessary elements for life.
So life as we know it – built on carbon chains, using oxygen to transport energy and immersed in a bath of liquid water – could be much, much older than Earth. Even other supposed life forms, based on exotic biochemistry, require a similar mix of elements. For example, some aliens use silicon instead of carbon as a basic building block, or use methane instead of water as a solvent. No matter what happens, those elements have to come from somewhere, and that’s somewhere in the cores of stars. Without starsyou can’t have a chemical-based life.
The first life in the universe
But maybe it is possible to live a life without chemistry. It’s hard to imagine what these creatures might look like. But if we use our broad definition – that life is anything subject to evolution – then we don’t need chemicals to make this possible. Sure, chemistry is a useful way to store information, extract energy, and interact with the environment, but there are other hypothetical routes.
For example, 95% of the energy content of the universe is unknown to physics and is literally outside the known elements. Scientists aren’t sure how these mysterious components of the universe are known dark matter And dark energyare made of.
Perhaps there are other natural forces that operate solely on dark matter and dark energy. Perhaps there are multiple ‘types’ of dark matter – a whole ‘periodic table of dark matterWho knows what interactions and dark chemistry are going on in the vast regions between the stars? Hypothetical ‘dark life’ may have appeared in the extremely early universe, long before the rise of the first stars, driven and mediated by forces we exert. don’t understand yet.
Related stories:
– Life as we know it may have its roots in an ancient, cold cosmic cloud
—Meteorites and volcanoes may have helped jump-start life on Earth
—Scientists recreate the possible origins of life in a laboratory
The possibilities could get even stranger. Some physicists have hypothesized that the forces of nature in the earliest moments of the Big Bang were so extreme and so exotic that they could have supported the growth of complex structures. These structures, for example, could have been cosmic strings, these are folds in space-time, anchored by magnetic monopoles. With enough complexity, these structures could have stored information. There would have been enough energy, and those structures could have reproduced themselves, making Darwinian evolution possible.
All beings living in these conditions would have lived and died in the blink of an eye, their entire history lasting less than a second – but for them it would have been a lifetime.