New research from a Harvard astrophysicist suggests the first life in the universe may have emerged just 10-20 million years after the Big Bang. This is a few billion years before most scientists believe that the universe had suitable conditions for the genesis of life. If life really did emerge way back then, and then continued to travel through space on the back of asteroids and other interplanetary debris, it would seem almost certain that a) Earth was not the home of the universe’s first life, and b) life on Earth arrived on the back of an asteroid (panspermia).
As it stands, our best method of locating extraterrestrial life — and thus solving the mystery of whether life is unique to Earth — is based on the concept of habitable zones. Basically, the only thing we know for sure is that Earth has the right conditions for supporting life — and so it stands to reason that, if we can find other planets that have a similar setup (an atmosphere, a nearby star, liquid water on the surface), we might find life. This is the theory of the “Goldilocks planet,” which has been popularized in the last few years by NASA’s Kepler telescope, and other similar endeavors.
Most scientists believe that, if there’s life out there, it’ll probably be on Earth-like planets in the habitable zone — like Kepler-62f (artist’s impression)
According to Harvard astrophysicist Avi Loeb, though, there was a brief period in the universe’s timeline — a period of about 7 million years, which Loeb calls the habitable epoch — where most of the universe would’ve been habitable by life. How? Cosmic microwave background radiation.
All throughout the universe, there is thermal radiation — cosmic microwave background (CMB) radiation — that’s theorized to be left over from the Big Bang. Today, the universe is so old and so large that the CMB only warms space to around 2.7 Kelvin (-270.45 Celsius, -454.81 Fahrenheit). Billions of years ago, though, just 10-20 million years after the Big Bang, the CMB would’ve kept the entire universe feeling like a “warm summer day on Earth” (Loeb’s words). For around 7 million years, Loeb says the conditions would’ve been just right for the genesis of simple life. [Research paper: arXiv:1312.0613 - "The Habitable Epoch of the Early Universe"]
An all-sky map of the cosmic microwave background radiation, from when the universe was just a few hundred thousand years old. The heat fluctuations eventually turned into galaxies.
His new theory has some logical flaws, though, which he readily admits. Most astrobiologists think that life couldn’t emerge during the first few billion years of the universe because it lacked the rocky planets and heavier elements that life (as we know it) requires. The current understanding of the universe is that heavier elements (i.e. carbon, phosphorous, metals) — elements that are needed for the genesis of life — are created in supernovae explosions. Just 10 million years after the Big Bang, the universe was full of hydrogen, helium, and not much else. It’s possible that even the first stars hadn’t formed by this point. Loeb’s explanation is that, just maybe, there were some rare regions of the early universe that were mega-dense, and thus could begin the whole star formation/supernova/rocky planet process sooner than expected.
Loeb says that this theory could be tested by searching the Milky Way for planets orbiting stars that contain no heavy elements. These planets would be similar to those that occupied the very early universe, and thus might tell us something about whether life began just 15 million years after the Big Bang. (Read: Alien spotting: By 2020, we’ll finally have the ability to locate life-harboring, alien planets.) If genesis really did occur that early on, when the universe was still very small and dense, it’s entirely possible that those life-bearing asteroids, meteors, and planetoids have been hurtling through space for the last 13.7 billion years, seeding large portions of the universe with life.
Source: ExTe
No comments:
Post a Comment