[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Does the earth wobble?



Of course the earth wobbles, but only by a degree or so   either
way.  The wo bbling is on such a short cycle that it is irrelevan
t to dino  extinction.

HOW LONG HAS THE MOON BEEN WITH THE EARTH?

Two lines of evidence point to the idea that the moon has been
around for about 4.3 billion years.
First, George Darwin simulated the t rajectory of the earth back
through time, and found that at about 4.3 Ga (gigayears, that is)
the moon was so close to th e earth that it was within the Roche 
limit, where  it could not have existed for long as a solid object
because of tidal effects.  I have done th e same simulation using
a different technique and agree with Darwin.
Second, there is the scenario that the moon originated after a
Mars-sized bolid hit the earth.  Lot's of  evidence for this one.
On this scenario, the cores of the two planets    fused (about
4.4 Ga) leaving a       fuzz of left over bits of the mantle
sculling around the  fused mass.  The stuff inside the Roche
limit fell back to earth, while that outside eventually
coalesced to form the moon.  This would account for the lack of
metallic core to the moon.   A recent paper in Science (May or
June this year), gives more credence to this scenario, showing
that th e far side of the moon is l argely made up of a mineral
that forms on the surface of molten rock, a material that is
rare on earth.  The general idea, then, is that the moon
coalesced, that the heat of accretion caused it to melt into
a blob th at solidified about 4.3 Ga.

Thus  whatever scenario we embrace for the origin of the moon
it started turning around the earth at about 4.3 Ga, either
formed from stuff thrown out by a collision,, or esle captured
after f o rmation somewhere else.

ARE BIRDS DINOSAURS

I applaud Jerry  Harris'comments on this topic.  From the
cladistic p oint of view birds must be considered to be dinos,
but classification should be useful.  I am joining Jerry in
his campaign to stay as a good ole Linnean.  I still want to
call the birds   a CLASS in the Linnaean sense, even if they
are desended f rom the Archosaurs.  That may not make cladistic
sense, but it sure makes more sense for all all the other uses
to which we put a classification.  Whatever the American
Museum of Natural History may say, I still say birds are a
class on their own.  That's a good exhibit, by the way. Saw it
in New York a co uple of weeks ago.

DID DINOSAURS JUSTD FADE AWAY?

Dinos do not make good markers for the K-T boundary.  They're
just too big and too rare.  Mocrofossils are needed as markers,
and they show a clean break at the K-T.

VELOCIRAPTOR & DEINONYCHUS?

They seem to be di fferent sp ecies of the same  genus to me.
The di fference in size could be significant at the species
level, but n ot between species of a  single genus.

The qu estion remains: which name h as priority?  Is Deinonychus
a junior subjective synonym of Velociraptor, or is Vel. a junior
subjective synonym of Deinonychus.  I suspect the latter.  Can
anyone  tell me?


David

--
>From: David Brez Carlisle
bk090@Freenet Carleton.CA