Evening star., 1949-02-25
Stars, Men and Atoms
Recurrent Ice Ages Seen
Due to Cosmic Dust Cloud
Variations of Suns Heat Believed Not
to Account for Periods
Bv Thomas r. Henry

The earth may have emerged from cos
mic dust cloud
This could account for the recurrent ice
ages, according to a report to the Ameri-
can Association for the Advancement Of
Science by Dr.. Donald H. Menzel of Harvard
University.
1t now is generally agreed, DR.. Menzel says.
that the cycle of warm and cold periods must
be in some way associated with the sun.
There have been four ice ages in the past
million years which cannot be accounted for
by anything happening on the earth itself.
Also the known variations in the suns heat
output are insufficient to account for the
great terrestrial temperature variations.
Extremely Thin Clouds.
1t is known, however, that space through
which the solar system is moving is filled
with titanic dust clouds. They are extremely
thin. There probably is no way by which
an observer on earth could be aware that
the planet was immersed in one OF them.
There would be little difference IN the
amount Of solar radiation actually received
on the earth's surface.
On the other hand DR.. MenZel says, a
considerable amount of the long-wave heat
radiation ordinarily going into space by the
earth itself would be retained. The climate
would become warmer-which is exactly
what is needed for the start of an ice age.
More water is evaporated. 1t falls as snow
over the poles. The snow is compressed into
ice and starts to flow southwark.
The hypothetical dust cloud in which the
earth may have been immersed for million
years. Dr. Menzel points out, probably was
thicker in some places than in others. When
the solar system was passing through very
thick portion this planet would be very warm
and semitropical forests might flourish In
he Arctic apd Antarctic Tn a relatively
thin cloud area the ice-building would start.
DR.. MenZel calculates that emergence from
the cloud occurred about $4,000 years ago
and that this planet is now about 100000 ,000,-
00,000 miles away from its outermost edges.
Two French insects-a tiny wasp and
hy-have Just been introduced to protect
America sweet clover.
They are the natural enemies OF the clover
weevil which in the past twenty years has
reduced the sweet clover crop by as much as
two-thirds in some areas and which is OF
growing concern to agriculture throughout
the country.
Sweet clover was originally a European
plant. Its growth now is quite general over
most of the United States and Canada.
Through countless generations in its home
lands the plant had become adjusted to its
enemies. The clover weevil whose small,
fat. white grubs feed on its rootlets. was
kept under control by a variety of other
insects which preyed upon it.
Grub Came in Shipments.
In the New World the weevil did not exist.
Consequently the clover fourished without
any need for protection. But in 1924 the
presence of the destructive grub was re-
ported near Montreal. 1t apparently had
come with some plant shipments and was
we'll established by the time it was detected.
It since has spread over most of the clover
growing areas Of the United States and
Canada.
Methods of combating it with various
insecticides have been fairly effective. but
laborious and expensive. The introduced
parasites have proved fairly effective in cage
tests, according to report to the American
Association for the Advancement of Science
by DR.. j. A. Munro of the North Dakota
Agricultural Experiment Station. The ques-
ton remains as to whether they will thrive
in their new environment.
The new insects, which are themselves
harmless to crops, were obtained by Agrl-
culture Department entomologists after
study of French crop conditions.