DATING THE EARTH’S CRUST—SHAPLEY 141 
The temperature of interstellar or intergalactic space can be vari- 
ously defined. When measured by the equilibrium temperature of a 
small meteoritic particle at a distance of a light-year or more from 
the nearest luminous star, it is probably but 2 or 3 degrees above abso- 
lute zero. But if we should “measure” temperature in terms of atomic 
and molecular motion, we could say that a radiant gaseous nebula 
(even though of almost infinitesimal rarity) at the distance of a light- 
year from a blue star has a temperature of 10,000° or 20,000° absolute. 
The first definition is the one to choose in considering the leakage 
or radiation from the surface of the sun, a leakage of 4,000,000 tons of 
light per second. The sun’s output of light would be enormously 
greater if we should peel off suddenly the outer 1 percent of its body. 
The skinning of the sun would expose highly ionized gases with tem- 
peratures in the millions of degrees. We would have a kind of super- 
nova, but only momentarily on cosmic time scale; for promptly the 
ionized atoms would regain their shells of electrons, some molecules 
would form, the present heavily absorbing atmospheric layers would 
re-form, and with some serious convulsions and oscillations set up by 
the sudden exposure, the sun nova would speedily return toward the 
calm equilibrium it enjoyed before we ventured the reckless experiment. 
It is quite likely that great gaseous envelopes might be produced 
by a sun-to-nova flare-up, or in course of the subsequent convulsions; 
and in any case, the earth and neighboring planets would be promptly 
scorched clean of biology and their surface features melted away. 
Clearly the sun has not been a nova since the freezing of the earth’s 
surface into its present state. 
These comments on the coldness of space and on the sub-surface 
hotness of the sun are all immediately relevant to the problems of the 
origin of the earth’s rocky crust. If the planets were generated 
catastrophically from the sun, much of the material composing them 
must once have been this highly superheated material that les not 
Tar below the 6,000° surface layers through which our present sun- 
hight is filtered and cooled; we must use not the relatively cool outer 
portions alone, for the total mass of the sun’s atmosphere is small 
compared with the mass of a planet. 
The greediness with which interstellar space, even interplanetary 
space, absorbs radiation is significant in its bearing on the age of the 
earth’s crust. Both elementary consideration and mathematical cal- 
culations indicate that any earth-sized gaseous or liquid body, isolated 
in sidereal space, would freeze into solid matter (rocks) practically 
instantaneously—again in terms of cosmic time scales. 
It is this quick transition from the normal, hot, ionized, turbulent, 
gaseous state of stellar matter to the relatively cold, dead, crusted body 
of a small or medium-sized planet that is important in bringing to- 
