Geology Reference
In-Depth Information
Fig. 4.12
M
-series segment of the geomagnetic po-
larity time scale of Gradstein et al. (
2004
). Only
the major anomalies are labeled. Numbers on the
upper scale are distances from the ridge when the
spreading rate is 20 mm year
1
.The
red line
shows
the
time scale in the case of an N-S profile in the
northern hemisphere. Ages of the labeled anomalies are:
M0
135.28 Ma,
M16 D 142.06 Ma, M21 D 148.54 Ma, M25 D 154.37 Ma,
M29 D 157.51
D
124.61 Ma, M5
D
129.76 Ma, M10N
D
Ma,
M37 D 162.04
Ma,
and
theoretical
magnetic
signal
associated
with
this
M41 D 165.61 Ma
Fig. 4.13
Earth's
magnetosphere and
interplanetary magnetic
field (
IMF
). Solar wind
streamlines are shown in
red
. Points
P
are polar
cusps. Field lines of the
Earth's magnetic field and
the IMF are shown
respectively by
solid black
and
blue lines
highly conductive plasma flow ejected by the
Sun, which travels at a velocity of
500 km/s as
a result of the supersonic expansion of the solar
corona. High conductivity of this material implies
that the magnetic field flow lines are frozen into
the solar wind plasma (see Sect.
4.1
). Therefore,
in the region where the charged particles strike
against the Earth's magnetic field, the particles
slow down and to a large extent are deflected
without penetrating the magnetic shield. At the
same time, the flow lines of the Earth's magnetic
field are compressed in the dayside region and
stretched out along the nightside area, generat-
ing a wide
magnetotail
(Fig.
4.13
). As a conse-
quence, the Earth's magnetosphere is a magnetic
cavity shaped like a comet head and tail, and only
at distances less than 5
R
e
,
R
e
being the Earth's ra-
dius, it can be considered approximately dipolar.
