Chirality is an interesting concept. The best way to explain it quickly is an analogy to being left-handed or right-handed. Molecules don't have hands, but they do have an inherent orientation that can be compared to having a dominant hand that you do most of your work with. Sugars are mostly right-handed. Amino acids: Left-handed.
But here's where things get weird: It doesn't have to be that way. In fact, given the randomness and chance through which evolution works, it would make more sense for there to be a lot more diversity in orientation.
All of this backstory is important so that I can tell you about the most hilarious non sequitur I've encountered in 2012.
Chemist Ronald Breslow has a new paper out in the Journal of the American Chemical Society, where he talks about why chirality might be the way it is. For the most part, his ideas are not unreasonable ones. Breslow thinks that life on Earth—and we're talking about life in its simplest forms, like molecules, not actual creatures—could have been "seeded" by material that fell to the planet on an asteroid. The idea is that, if the building blocks of life came from one place—a meteor fall—rather than arising and adapting here, it could explain why there's not the diversity of molecular "handedness" that we might otherwise expect to see.
In fact, in related news, there's another paper out suggesting that Earth could have paid that gift of life forward, with potentially microbe-and-molecule-laden rocks from here traveling far into interstellar space.
What makes Breslow's paper unique is the odd, brief, speculative tangent he gets into at the very end, a tangent which lead to me receiving a press release titled, "Could Advanced Dinosaurs Rule Other Planets?"
An implication from this work is that elsewhere in the universe there could be life forms based on D amino acids and L sugars, depending on the chirality of circular polarized light in that sector of the universe or whatever other process operated to favor the L α‐methyl amino acids in the meteorites that have landed on Earth. Such life forms could well be advanced versions of dinosaurs, if mammals did not have the good fortune to have the dinosaurs wiped out by an asteroidal collision, as on Earth. We would be better off not meeting them.
I suppose it's rather hard to argue with the basic thesis that we'd be better off not meeting a hyper-intelligent T. Rex. But at Dinosaur Tracking, Brian Switek attempts to explain why it's maybe not a great idea for chemists to randomly start pontificating on paleontology. In particular, the "rule" of the dinosaurs was not inevitable and was not dependent on the outcome of a single asteroid collision.
Prior to 250 million years ago, the synapsids—our ancestors and relatives—were the dominant creatures on land. But the apocalyptic extinction at the end of the Permian Period eliminated most synapsid lineages, in addition to many other forms of life. This clearing of the ecological slate is what allowed a different group of creatures to proliferate. Early archosaurs, or "ruling reptiles," included the archaic forerunners of crocodiles, pterosaurs and dinosaurs, in addition to various groups now extinct, and these creatures dominated the Triassic.
Despite what has been traditionally told, though, the dinosaurian branch of the greater archosaur family tree didn't immediately out-compete its neighbors. Eoraptor and Herrerasaurus were not the Triassic terrors they were cast as during the mid-1990s. For the most part, Triassic dinosaurs were small, rare, marginal parts of the ecosystems they inhabited. It was only after another mass extinction at the end of the Triassic, around 200 million years ago, that the competitors of early dinosaurs were removed and the reign of the dinosaurs truly began.
Image: Dinosaur, a Creative Commons Attribution Share-Alike (2.0) image from shvmoz's photostream