Old Times Not Forgotten

Age: Radioisotope 207Pb/ 206Pb dating of refractory inclusions (CAIs) found within chondritic meteorites, the oldest Solar System solids known, yields an age of 4.568 Gyr. Dating with other isotope systems yields similar ages. Chondrules, as well as most differentiated meteorites that originated within small bodies, solidified only a few million years later (§ 8.7). Rocks formed on the Moon and Earth are younger: lunar rocks are typically between 3 and 4.4 Gyr old, and terrestrial rocks are ≲ 4 Gyr old, although terrestrial mineral grains as old as 4.4 Gyr have been found.

de Pater, Imke; Lissauer, Jack J.. Planetary Sciences (p. 512). Cambridge University Press. Kindle Edition.

The ages of the refractory inclusions and the chrodrites tell us when they first solidified, almost certainly when the solar system was first condensing. From studies of regions of stellar formation, and deductions from basic physics, we know that stellar systems form in relatively dense molecular clouds containing a lot of dust. As the most of the mass concentrates in the star (I'm not considering multi-star systems here) most of the angular momentum ends up in the outer reaches which are flattened into a disk by gravity and viscous dissipation. The micron sized dust particles in these disks stick together, accumulating over a few million years into planetesimals each formed from roughly a trillion, trillion, trillion (10^36) dust grains.

Comments

Post a Comment

Popular posts from this blog

Anti-Libertarian: re-post

The most pointed critique of social security and liberalism in general is the libertarian critique. The problem with libertarians, for a liberal, is that we have too much in common. We both believe in individual rights, tolerance of individual differences, and dislike government prescription of religion. The basic difference, it seems to me, is the different answers we give to Cain's (with thanks to the Captain - my original version had the corpse asking the question!) famous question: "Am I my brother's keeper?" That's not really my basic bitch against the libertarians though. My real complaint is the same as my complaint against most religion - its premise is a fraud. For those who can't stand to wait for the punchline, I believe that trying to implement libertarian principles leads to tyranny or social disintegration. Demonstrating that takes some historical (and pre-historical) context. For all but the last 15,000 or so of the 100,000 years the human spec
Read more

Uneasy Lies The Head

Uneasy lies the head that wears a crown ........... Shakespeare Henry IV, Part II. So it is with us and our slightly distant primate cousins , so it seems. A 9-year study of wild baboons in Kenya by Princeton University and the Institute of Primate Research may turn conventional assumptions of alphas males upside down. The study found that alpha males have high testosterone levels, which allows them to dominate other baboons, get access to more food, and attract better mates. This is expected. Surprisingly, though, the alpha males also have high levels of stress hormone glucocorticoid, which scientists measured from their feces samples. In fact, the stress of alpha baboons was on par with low-ranking baboons. The convention wisdom is that access to food and females provides life security and thus less stress for dominant males. Conversely, weak males who are constantly threatened by starvation and physical violence from stronger males are thought to be more stressed. The st
Read more

We Call it Soccer

The US played its best, and maybe only good game of World Cup, but lost thanks to brilliant goalkeeping by the Swedish keeper and the bizarre method soccer uses to settle ties when three US stars could not put the ball on frame from the 12 yard spot.  At the end it came down to a blocked shot that spun in by maybe a couple of centimeters. Well, that's football - too much like life.   Which brings me to a modest proposal.  Replace the thirty minute overtimes with as many 7-player 15 minute periods as needed to settle it.  Scoring should be much easier with fewer players.
Read more