| 2961/
On Easter Sunday, March 27th, 1513, Juan Ponce de Leon sailed
from the Bahama island of San Salvador with three ships. He
set out to discover a spring said trestore "age'd men
to youths" that was to be found on the island of Bimini.
He did discover a "spring" of sorts - a swift-flowing
ocean river called the Florida Current, part of the Gulf Stream
system of currents, which swept his ships far off course.
2962/ Continental basement
rocks are "granitic"; they contain a high proportion
of silica and aluminium. The seafloor crust is "basaltic";
it contains less silica and a high proportion of iron. Continents
are therefore lighter than the ocean floors - like inebergs
trapped in sea ice.
2963/ This accounts for
the average 5km (3 miles) by which the continents are elevated
above the seafloors. Since water always gravitates to the
lowest point on any surface, it also accounts for the location
of the oceans.
2964/ The Earth's north
magnetic pole was discovered in 1831.
2965/ After its first
discovery, the magnetic pole was rediscovered in 1903. It
had moved a considerable distance. Todays magnetic polar region
is nearly 800km (500 miles) NNW of its 1831 position. Such
movement, during a relatively short period of time, may be
a prelude to a complete reversal of the Earth's magnetic field.
2966/ The Earth's magnetic
field has switched irregularly from north to south and back
again innumerable times in the geological past in response
to changing dynamo currents in the magnetic molten core of
the Earth's core. The last reversal (from south to north)
occurred about 700,000 years ago.
2967/ Ellesmere Island
in the Canadian High Arctic is separated from Greenland by
Nares strait. The narrow strait is over 480 km (300 miles)
long and at its narrowest point only 25km (15 miles) wide.
This is the site of an ancient suture between Greenland and
North America.
2968/ It was many years
before the proof of seafloor spreading and relative continental
movement was broadly accepted by the geoscience community;
the proof was in place by 1965, but the theory of plate tectonics
that evolved from these discoveries was not embraced until
the early 1970s.
2969/ The shape of the
Earth is called the geoid. It is oblate - flatter at the Poles
than at the Equator. But it changes as the planet resonates
during its spin and responds to gravitational forces. Also
it is either depressed or uplifted by the varying weight of
ice on land or the distribution of shallow seas and oceans.
2970/ The Earth's core
consists of two intimately related spheres. The outer core
is a white hot semi liquid. It is composed mainly of iron;
other elements include nickel and sulphur. It is about 2,250
km (1,400 miles) thick.
2971/ The inner core
is a solid sphere of iron-nickel alloy with a radius of almost
1,600 km (1000 miles).
2972/ The mass of the
Earth's core (31 percent) combined with the mass of the mantle
and the asthenosphere (68.3%) make up 99.3 percent of the
Earth's mass.
2973/ This leaves only
0.7 percent to account for the entire weight of the Earth's
lithosphere - the thin rind of crust that includes the continental
masses and supports the oceans.
2974/ The oldest known
animal fossils on Earth are called "Ediacara" after
a locality in Australia where they were first discovered.
2975/ The oldest known
amphibians include Ichthyostega, a carniverous creature that
could open its jaws wide enough to attack, kill, and feed
off large victims - including other Ichthyostega.
2976/ According to the
fossil record, land plants first appeared around 420 million
years ago.
2977/ In Greek mythology
Tethys was a sea goddess, who with her brother Iapetus - of
Iapetus and Avalonia - was descended from Gaea, mother of
the Earth.
2978/ Between 255 and
250 million years ago more than half the species of animals
on Earth, including 75-95 percent of marine species, were
permanently extinguished. This mass extinction is the greatest
such event found in the fossil record.
2979/ Death Valley is
one of the hottest desert regions on Earth: the highest recorded
temperature there is 57.1 centigrade (134 F) in the shade.
2980/ Protoctista (minute
life forms) are truly the artisans of the geological world,
for they make (with their skeletal remains) over a billion
tons of carbonate rock a year. They also make oil - in Cretaceous
times, over a period of 30 million years, they produced perhaps
70 percent of the presently known global reserves of oil.
Click on the links below for more great
facts...
More
next week... |
