时间:2019-02-23 作者:英语课 分类:英语时差8,16


英语课

By calculating how old the rocks are where we find these ancient compasses, we can figure out how long ago the magnetized parts were locked in. That tells us which direction was magnetic north tens of thousands of years ago. Surprisingly, it’s not always the same as north is now. Occasionally the poles change places. So, did the north pole drift slowly southward, so that at some point magnetic north was in, say Mexico city? No. The rocks tell us that, during pole reversals, there is a several thousand year period during which the earth’s magnetic field is either gone or very much weakened. At these times north and south become arbitrary terms. Eventually the magnetic field re-establishes itself, and it seems to be a matter of chance which side comes out north and which south.



学英语单词
air pollution source
anterior tentorial arms
anti-Semite
antimony compounds
Aponogeton
apple dumplings
Arab League
assia
belimbings
Bertram Brockhouse
bioeffect
Bombyliidae
borsal
carries point
circumscriptible
co-uned
collegiate panel
completion status
coupled thermal-nuclear model
custodial sentence
cybervillages
diffraction grating
Dymnamic Host Configuation Protocol
echiodon coheni
electronic typhonic equipment
ergochrysin
extension of a group
Ficus ischnopoda
flory
frontfired
GALEASPIDIFORMES
gastrointestinal forceps
Gayer tests
general instruction to tenders
hand mower
have a sale
hydraulic mill
ilicfemoral ligament
incoming gas
intake conduct
ion ray
iterative computing
killex
LAN card
laography
literary genre
lithia mica
LQ problem
magneto-crystalline
marmor serpertinatum
metzlers
MIME encoding
mixed wet feed
morus alba l. var. skeletoniana schneid.
multi-processing
multifossil range zone
multitasks
Naantali(Nantali)
non-whites
onthophagus (onthophagus) terminatus
Ophthetic
Orion Aggregate
osteoglossids
parapsoriasis maculata enplaques
personal decision analysis
Pilgrim Festivals
power-limitings
prestigiatory
pseudonymously
quickmunch
rapability
raw starter)
red-legged partridges
repliest
return block
revolving-screen washer
roll turning shop
ruffsides
safebreakers
Schumm's test
scour resistance
self-induced magnetic flux
septation
sheet-pile breakwater
shmendrik
short-delay line
single prism spectrograph
sinker plate
slap print
sparra
srta
step to the fore
target droneaircraft
Townville
track shim
trichechidaes
Trifluvians
us jibe
visitours
wauf
wing bay
Withington, Mt.