Et tunc nulla erat II
(And Then
There Was)
Derived
Expansion:
Have you ever looked at a world globe
and wondered how it ever got to look like that. Well I can tell you for sure
our world in all its evolutionary stages did not always appear as it does today,
far from it and will change its face once again many times more before lights
are totally out. Where once there was an oceanic seafloor under the long gone
Tethys Ocean is now 26,000ft/7,925m above sea level alpine land in the
Himalayan mountain chain supporting glaciers.
Let’s journey into the past to explore
our present shall we…
From that supernova burst and accretion
of its blast debris, Earth had parked in its own solar system revolving around
an infant star as just evolving from the womb of its protosun stage some 4.6
billion years ago (bya).
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Early Earth Computer model |
In its initial own infancy Earth was
void of its oceans and had no companion as its satellite the moon was to come
later. Studying isotopes of elements embedded in Earth’s earliest mineral
accretions detect a gestation period of 50-100 million years before our home
was fully formed. But in this initial infancy, Earth was primarily a mesh of
molten minerals and metal and smaller than it is now. The denser metals sank to
the core while lighter material raised more to the surface as Earth gradually cooled.
Around 4 bya felsic zircon crystals were formed from the earth’s crustal
cooling that have now been located as deaggregated and redeposited sediment in
Western Canada’s Canadian Shield and in Western Australia’s Jack Hills region.
Ranging from 0.1mm to several centimeters in size, zircon or zirconium silicate
is extremely hard and with its chemical inertness and tetragonal crystal
structure can endure erosion, metamorphism, magma and redeposition into other sediment
material. Zircon has survived a very long journey.
The main elements that clue us to
Earth’s formation come from compilations rich in aluminum and calcium that
formed during the solar system’s infancy of accretion. Today, these two
elements can be found in meteorites as inclusions embedded in carbonaceous
chondrite. Meteorite inclusions are more known in their euphonic form as CAIs
for Calcium-Aluminum-rich Inclusions. These inclusions found in
meteorites prove to be 50-100 million years older than Earth.
Earth’s very infancy is known as the
Hadean Eon ranging from 4.6-4.0 bya. It was so named by American geologist,
Preston Cloud (09/26/1912-01/16/1991), for Earth during this period had a
molten to a slightly cooling surface, was full of raging volcanism, choking
gaseous fumes with nothing but steaming water not yet able to condense. It was
a time of incessant bombardment along from micro-dust to much larger accreted solar
system bodies. In being such a hellish environment, Cloud decided Hadean for
Hades would be an accurate coining as Earth truly was in this eon a vision of exactly
what we imagine Hell to be.
Cataclysmic chaos ensued during the
Hadean Eon. In fact, the first half of the Hadean Eon is called the Chaotian
Eon as classified by NASA scientists. They also call the very earliest portion
of Earth solar nebula formation as the proto-planet, Tellus and once the
proto-planet Theia smacks into Tellus, in which we’ll discuss in the next
chapter, they then call the two proto-planets as combined…Earth.
After 500 years of its accreted
formation, Earth’s original hydrogen and helium atmosphere was lost to outer space
as these two lightest elements reached escape velocity due to the extreme heat
in Earth’s molten state. Earth could though, support an atmosphere with its mass
gravity holding down all heavier volatiles that were liberated as gases from
the collisions. Breaking gaseous prisons as locked interstitially between
impactor grains and held under Earth’s interior, volatiles began forming the
atmosphere. But it was not mainly methane as was once perceived. In veritably, as found in dissolved gaseous
compositions in deep crustal or upper mantle magmas, the atmosphere first leaned
more to an oxidized state rather than reduced tied into compounds such as
water, carbon dioxide and sulfur dioxide. The total percent of free oxygen
radicals although were much lower at ~3.8% than now at its current 21% make-up
of the atmosphere. Nonetheless, as nitrogen is chemically inert, free nitrogen
was already becoming the main component of Earth’s atmosphere and later to
become the Earth’s first elemental recycle.
As mentioned, Earth during the Hadean
Eon was constantly being pummeled by extra solar debris. All kinds of heavenly
material were raining down from the young solar system pulled in by Earth’s
gravity tug. Solar winds as irradiated charged particles generated from the sun’s
upper atmosphere were smashing at will at supersonic speed into Earth as the
magnetic field was not up and running yet, which deflects most of today’s solar
winds. Grain sized dust to comets composed essentially of ice, a bit of dirt
debris and rock pebbles continuously showered Earth’s surface. Comets were to
be a great water source for Earth’s later forming oceans. Meteoroids, basically
leftover small debris objects orbiting through the solar system’s
interplanetary space are no bigger than one meter (3.3 feet) in diameter with
solid mass composed mainly of silicate rock where around 6% are dense
iron/nickel. As meteoroids fall through Earth’s atmosphere they are termed
meteors whether surviving landfall or not. For those that do not burn up in the
atmosphere and hit land, they are known as meteorites, which under analysis
have told us a lot about the early solar system’s composition and timelines.
Asteroids are essentially meteoroids on
steroids. They are much larger bodies primarily with their own orbits and may
be considered as minor planets being a few hundred meters or miles in girth known
as planetesimals with the largest ones in inner space further called
planetoids. Composed mainly of mineralized stone and metals, some are carbon
rich and indeed during the Hadean Eon, many asteroids that smashed into the
infant Earth planted their organic seed…the basis for all Earth’s life.
Most asteroids remain in the asteroid
belt between Mars and Jupiter and were evolving as they were accrediting into
planets or one enormous one. But during Jupiter’s formation, its strength in
mass during orbital resonance impacted planet evolvement in the asteroid belt
ejecting 99% of the planetesimals from the original belt region. The three main
ejected asteroid belts have names known as Greeks, Hildas and Trojans. There
were many asteroids ejected further away from the belt into inner and outer
space. The ones ejected into inner space are the ones that have and may still
hit Earth.
Within the belt itself, orbital
resonance, which is a force similar to a parent pushing a child on a swing,
caused collisions breaking the planetesimals into smaller fragments, but held
them in situ about the belt’s current orbit never again having the ability to
accrete and evolve into a planet. Some of the largest asteroids, bigger than
129 kilometers or 75 miles wide may have melted during this Jovian influence on
the belt, but did not fragment, instead differentiated with the heavier metals
sinking and the lighter rocky minerals remaining on the surface region.
Still though, even today during
Jupiter’s gravitational perturbations, a few asteroids in the Trojans conglomerate
are tossed out of resonate orbit into an unstable renegade orbit that can
collide with other celestial solar system bodies such as Earth. During the
Hadean Eon, this was much more frequent.
Amid the Hadean Eon’s onslaught of
comets, asteroids and meteorites pelting and smashing into Earth, around 4.5
bya, a huge boulder about the size of Mars, named Theia impacted Earth. This
smashup hurled molten debris careening in every direction. The initial collision
did not totally annihilate the impactor mass as it was more of a glancing off
center blow rather than a direct hit, but somewhat rebounded it back into sub
orbital space about Earth for approximately a half an hour only to be drawn back in slamming
into Earth once again. This time however, the whole of Theia was absorbed incorporating
into Earth’s mass.
Due to velocity statistics, the earth
and moon’s gravitational flux towards one another, the fact that Earth was around
half its current size with composition consisting primarily of the initial
solar nebula accretion and along with computer simulations bearing it out, we
know this is how the impact occurred.
This impact was crucial for what the
atmosphere was to evolve into. The impingement instantly vaporized a goodly
amount of material creating a vapor of rock composition in the atmosphere. The
so called rock vapor condensed within a matter of two thousand years dropping
the solid mineral constituents while leaving behind the hot volatiles. This
resulted in a heavy carbon dioxide percentage in the atmosphere along with a
substantial amount of water vapor.
The initial molten debris sent into
space was first mainly from the Theia impactor. The second and final impact
though, mainly hurled molten Earth mass outwards into space. The molten
material began orbiting Earth in rings much like is witnessed by Saturn today.
Around 22,531km/14,000mi above Earth, the molten material began accreting
forming what was to become the moon, which took only a half hour or so. We know
all of this due to the current angular momentum interacting between the
Earth/Moon dance.
Further verification of this moon formation is that most of the moon’s elemental and mineral crustal compositions are like Earth’s while oxygen isotopes found in both crusts are identical where other celestial bodies, such as meteorites, asteroids and Mars have differing oxygen isotopes much unlike the earth and moon’s. Other likenesses between the moon and the earth is that most mineral content in rock is not hydrated, but there is plenty of free water as found on the moon’s shadows in solid form (ice) or in water’s three forms of solid, liquid or vapor on Earth.
The newly formed moon took only ten
years to configure, but was still molten material. Due to remaining debris from
the original impact of Tellus and Theia, the moon, with very little or no atmosphere,
was constantly pelted by material being captured from its weak gravity. Once it
solidified, it was further hit by incoming meteorites and asteroids kicked out
of the asteroid belts by Jupiter.
It appears the moon had a little sister
moon forming as well about a third the size of the moon when our moon was a quarter
smaller in size. Within 100 million years the mini sister moon smashed hard
into the side of the lunar surface that never faces Earth. This smash up
created the highlands that is nowhere else evidenced on the rest of the moon’s
low plains surface we call Maria.
The moon is not spherical and is
certainly not circular, but is egg-shaped with one end pointed directly towards
Earth and the other small end on the opposite side of the moon that never faces
Earth. All this is due to Earth’s gravitational effects bulging the moon
end-on-end slowing its rotation.
As mentioned, the moon first formed only
22,531 kilometers or 14,000 miles from Earth. Ever since its inception though,
it has gradually been moving away going higher up in its orbit traveling
3.8cm/1.5in per year, where it is currently 384,400km/238,900mi in distance from
Earth. In robbing some of Earth’s rotational energy, the moon is still scooting
away from Earth where in another 4 billion years will only look like a big
bright star from Earth.
To end on the moon, we all look up into
the night skies and see only one satellite of Earth’s greeting us, but in
technically speaking, Earth indeed does have two satellites. There is an
asteroid caught in the earth’s gravitational pull that is 4.8km/3mi wide known
as Cruithne. Besides its small girth, another reason we never notice it is
because its closest point in orbit to Earth is 12,000,000 kilometers or
7,500,000 miles distant. In having a fainter magnitude than Pluto, one would
need a 320mm/12.5in reflecting telescope to image it. Though it orbits the sun
in a year’s time just like Earth, its bean shaped orbit around Earth takes 770
years to complete. It appears though, Cruithne is merely a hitchhiker, for in
another 5,000 years or so, it will be released from Earth’s gravitational grip
as Earth pulls away from Cruithne’s bean shaped orbit.
Catastrophic
Evolution:
Towards the end of the Hadean Eon, the
solar system began settling down. Earth’s surface was still an ocean of magma,
but the hurling of celestial objects had settled somewhat enough to allow the
earth’s crustal material to begin solidifying. By this time with the sinking of
iron and nickel, Earth had its patterned structure of a molten metallic core, a
predominately solid silicate rocky mantle with a chemically distinct crust
acting on the surface.
4 bya marks the ending of the Hadean Eon
and the beginning of the Archean Eon. All was relatively quiet at this
timeframe until 3.8 bya when a catastrophic event ensued directly from the
heavens. We are just now beginning to understand how planetary formations and
planetary orbits have a direct effect upon one another.
We’ve already discussed the influence
Jupiter had on the asteroid belt, thus affecting the whole solar system. Along
with Jupiter, the other three giant planets, Saturn, Uranus and Neptune
embarked upon an evolution of the solar system that was to abruptly change the
course of the growing solar system. It’s called by astrophysicists the Late
Heavy Bombardment.
The four giants were originally formed
together closer to the sun in very tight circles, with Uranus actually being
the outside planet and one farthest from the sun. Further still, there was a
dense comet belt stationed beyond Uranus. Being in close proximity, Jupiter as
the largest planet, creates a gravity pump forcing Saturn closer to Neptune and
Uranus. Saturn’s affected slowing orbital period around the sun grows to twice
that of Jupiter’s. All this perturbation drives the planets into the comet
belt’s proximity which flings comets in every direction until the belt was
nearly depleted. Once the belt was virtually swept clean of its comets, Uranus
and Neptune switch orbits ending the bombardment period, but forever changing the
solar system’s and indeed Earth’s evolution.
Although the bombardment lasted no more
than 0.3 billion years, Earth and its moon were literally hammered by this
bombarding event. The renegade comets brought an enormous amount of water to
Earth and the moon where it froze on the shaded lunar surface, while it was
held on Earth by its heavier formed atmosphere.
Although due to the dynamism of Earth’s
geologic features of subduction zones and volcanism, no extensive crustal cratering
remains from this event. The lunar surface however is intensely cratered and
the radiometric dating of the lunar impact melt rocks brought back by the
Apollo missions bear it out.
For sure the moon has been used heavily as
a heavenly punching bag. Lunar (moon) mountains are not the result of orogeny
but are rather from celestial impacts that have created mountains as tall as
2.25km/1.40mi. Lunar mountains took their permanent shape incredibly fast. Most
were formed within ten minutes. For fun, in using a little bit of simple
algebra, trigonometry, an astronomical almanac and a handy CCD (charged coupled
device) camera, one can calculate lunar mountain heights right in the
convenience of one’s own backyard.
Throughout the heavy pelting of asteroid
and meteoroid collisions and assuredly along with the Theia impact, Earth had
garnered enough iron that during its molten stage, the metal quickly sank to
the core and there an alloy of iron and nickel make up the composition.
Variable
Push to Life:
By 3.45 bya, still in the Archean Eon,
Earth’s metallic core was stable enough to initiate a magnetic field. This was
a very important event. The metallic core is divided with the solid inner core
at 1,250km/778mi thick (about the size of the moon) and the molten outer core at
2,200km/1,367mi thick. What makes the inner core a crystallized solid is the
intense pressure reaching 345 GPa. That is incredibly a lot of pressure. ‘G’
stands for giga (billion) and ‘Pa’ is for Pascal, an international measurement
of pressure. One GPa is 1,000,000,000 (billion) pascals and while 101.325
pascals are equal to 1 atmospheric pressure (atm) 345 GPa is 3,450,000,000 atm.
This pressure increases in magnitude iron’s melting point and equivalent to
45,000,000 psi, the metal crystals are forced to vibrate in situ as a solid.
Extreme heat is at play here too. In the inner core, the temperature range average is 5,430 °C or 9,800 °F with long play peaks at 6,093.33 °C/11,000 °F along the inner/outer boundaries, which is hotter than the surface of the sun. Inner core heat dissipates into the outer causing the solid inner core to creep into the molten outer core growing the inner core about 1cm/0.4in every thousand years. Heat from the outer core is further dissipating into the mantle making it a very viscous molten consistency of elemental, mineral and rock material. In the mantle is where most of Earth’s heat is stored.
All this original core heat has been
induced by several factors where dense metals attract and absorb heat more
readily than insulated material. Expansion of the inner solid core generates
negligible latent heat much like liquid water giving up heat in turning to ice.
Extreme pressure from the original buildup of gravitational friction has played
a 5-10% part in generating heat. The vast majority of heat, at least 90% of it,
is fueled by radiation decay of radioactive isotopes such as Uranium-235, 238
or plutonium-40. In a radioactive isotope’s quest for stability, heat is
released as it sheds energy.
All this heat transference from the
inner core, along with Earth’s rotation causes the outer core’s molten iron to
move. These rotational forces acting upon the molten iron leads to weak
magnetic forces about the earth’s axis of spin. Along with the dynamism between
the inner/outer core boundaries with a more fixed resistant flow versus a more
turbulent flow, electrical charges are set in motion producing a weak magnetic
field.
The magnetic field being configured was
crucial in protecting surface quantities that were to be the seeds of life.
Solar winds, being ionized gases of charged electron and proton particles
blowing outward from the sun at 400km/248.55mi per second, would erode early Earth’s
atmosphere and dissipate water vapor out into space. The winds would also sweep
away the ozone protective layer allowing much more intense solar UV radiation
to bathe the earth’s surface that would have been biologically too damaging. This
is what appears to have happened to the current Martian low barometric atmosphere
where there was evidence of once vast amounts of surface water, but virtually
not a drop today.
Another critical aspect of the core heat
was Earth’s internal movement. Core heat began influencing convection currents
on the viscous mantle. Heat traveling from core to mantle not only turned
material into a viscous state, the radiating heat also created movement. The
semi molten mantle was and is a consistency of thick glue, but composed of a
myriad of material. It is a witch’s brew being stirred ever so slowly with the
bulk consisting of rock forming silicates, water vapor, various elemental and
compound gases such as boron (B) and mercury (HG) as vapors, noble gases in a
hybridized pyroxenite fluxed state, carbon dioxide (CO2), carbonates
(CO32-), hydrogen sulfide (H2S) and elements
such as sulfur (S) and metals. The mantle ranges from 7km/4.35mi to
3,961km/2,461.25mi in thickness.
As the heat disperses throughout the
mantle it cools as it rises, this in effect promotes heated movement as the
denser material cooling above begins to sink back into the bottom of the
mantle. This creates a circulation of convection movement. Just as the solid
inner core creeps into the liquid outer core at their interface, so too does
the mantle solidify in a thin layer between it and the earth’s crust.
The earth’s crust is composed of
solidified mantle material that is enriched in silicon dioxide (SiO2)
rock material, such as andesite and is transformed into various mineral
compositions of igneous, sedimentary and metamorphic rock. The crust also
contains the bulk of Earth’s incompatible elements within continental (land) crust
and basalts within the oceanic crust. Contributing only to ~0.473% of Earth’s
total mass, the crust is rather thin from 5km/3mi in oceanic crust to 50km/30mi
in continental crust.
Between the upper reaches of the mantle
and the belly of the crust is a region of magma under a state of molten liquid.
In having liquid form sandwiched between two solids, the liquefied material is
under intense pressure. Magma is composed of mantle/crustal interchanged molten
solids, dissolved gases and some heat resistant crystals such as zircon. Crustal
material has elasticity and behaves much like semi-plastic. Rock material under
stress though, does crack and breaks when strain reaches fracture limits of the
material under intense pressure and heat. With a thin crust, rupture zones indeed
commence creating fissures, vents and volcanism that release immense amounts of
lava (the molten solids of magma) onto land and liberated gases into the
atmosphere. Intrusions into adjacent rocks with pressure opening up fracture
sensitive zones also are avenues for lava extrusion.
From this, the original atmosphere of
hydrogen and helium did evolve into other percentile gases from Earth’s own
mechanics utilizing the bombardment materials from outer space, with the core’s
engine generating the heat necessary to fuel the process. A complexity of
events that took hundreds of millions of years to conduct, we now know all today
was not created as from a day one of creation. Today’s roughly 75% nitrogen/25%
oxygen atmospheric ratio also had to evolve.
Convection zones in the mantle also had
another adverse effect on the crust and in particular its surface. As heated mantle
convection currents meet and rise they converge forming spreading ridges
fracturing the thin crust just above with an effluent flow of magma out onto
the crust’s surface through volcanoes and seafloor spreading. This creates new
crustal material, but if there was no balance the earth would continue growing.
Fortunately for life as a whole, there is a recycling of crustal material
balancing addition with subtraction. As new material comes into play in the
formation of new crust, older crustal material is taken in from subduction
zones (trenches) where convection currents meet and sink deeper into the
mantle. See below figure:
This recycling of material between the
mantle and crust is biologically very important. Earth’s angle of rotation
allows all points of Earth’s surface to be showered in sunshine. If there were
only zones of spreading new material, the Earth’s surface would only grow
deforming its point of rotation about its axis severely affecting overall
sunlight exposure keeping certain regions in permanent shade. It could also
wobble Earth outside its current orbit. Just a few degrees closer to the sun
the earth would scorch and likewise, a few degrees distance further, the earth
would freeze. With only subduction zones gobbling up crustal material the
dynamism of Earth would essentially be dead with no new influx of material. All
orogeny would erode down to plains and below sea level.
There is still another influence of the mantle’s
convection currents on the crust…continental drift.
Land masses we deem as continents are
essentially islands riding atop tectonic plates comprising the crust and upper
most solidified mantle in a zone called the lithosphere. The word lithosphere
is derived from ancient Greek meaning rigid rock. Tectonic plates in turn ride
on the back of the rheological viscous upper mantle. The major source of plate
movement is powered by the geodynamic mechanisms of convection currents. This
involves complex mechanical processes in the differences between the solid and
rigid lithosphere along with the prone to flow rheology of the mantle.
Also with the lithosphere, heat is lost
by conduction while heat is transferred by convection from the upper mantle.
The upper most portion of the upper mantle is known as the asthenosphere. The
asthenosphere is mechanically weak and readily deforms under tensile stress.
This characteristic is known as ductility and is dependent on pressure and
temperature. The element gold (Au) is high in ductility.
In transferring heat by convection, along
with its highly viscous material, the asthenosphere has an adiabatic
temperature gradient. An adiabatic process can be very complex and for purposes
here we will not go into hardly any detail. If there is any further enthusiasm for a few, the graphic below might be of some interest.
To be brief, before we steer completely
away from our main thoughts, we usually think of flames deriving from burning
organic material such as wood or gas in oven ranges where a constant pressure
adiabatic flame temperature is confined to a narrow range of 1950 °C/3542 °F.
This is due to the stoichiometric combustion of organic compounds where carbon
materials break down from C-H, C-C and 1.5n
O2 bonds to CO2 and H2O bonds. In open air
there is no confinement and as a result, the burning organic substances
decompose at a constant pressure allowing the resultant gassing to expand.
Beneath the earth, it is an entirely
different environment. In the boundaries of the lithosphere and asthenosphere,
the constant pressure adiabatic flame temperature (although there is no actual
flame without sufficient oxygen) results in complete combustion occurring
without any heat transfer or changes in energy whether potential or kinetic.
Therefore, temperature is lower than the constant volume process due to energy
utilized to change the volume system, or in other words, as in the first law of
thermodynamics…generate work.
As opposed to an open air flame known as
a diathermic wall where facilitated environment is conducive to transferring
energy, within the earth an adiabatic wall is one that halts any transfer of
energy from one body to another, acting essentially as prime insulation. This
is the driving force of the convection currents within the mantle in
maintaining energy levels and not dispersing it out through the crust.
There are secondary forces as well that
play minor roles in the convection currents’ effects on plate tectonics. Tidal
drag from the sun and moon’s gravitational forces exerting on the crust is one.
Others are basal drag driving plates by friction, shear strain due to the N-S
compression exerted on Earth’s rotation, subduction drag, gravitational slide spreading
and even the Coriolis Effect plays a minor role.
At the beginning of the Archean Eon,
Earth’s heat flow was three times what it is today and was two times that when
the Archean Eon ended. But Earth did cool down enough to form a thin crust
during the Archean Eon, though there most likely were incomplete pockets of
persistent lava. Convection currents began 4 bya and plate tectonics were well
in place by 3.5 bya being similar to that of modern Earth.
There are seven major plates, but while
depending on interpretation of a definition, there are eight major plates with
numerous minor ones. Lateral relative plate movement ranges from
0-100mm/0-3.94in annually, while plate motion ranges from 25mm/0.98in per year
(which is about the same as fingernail growth rates) to 160mm/6.30in per year,
which is about the rate of hair growth.
Where plate boundaries meet, geologic
forces take hold and with specific characteristics are descriptively named due
to their nature. When two moving plates converge on their borders and the one
most dense and heavier is forced underneath (subduction zone) or two with
similar densities collide (continental collisions) pushing upwards are all
classed as convergent boundaries. Convergent boundaries are destructive in that
the hydrous minerals in the subducting slab release superheated water melting
the mantle forming volcanism. Continental collisions are a variation event where subduction has been halted with force pushing the two plates upwards as they converge into one another, or one plate in its movement is forced upwards against a stationary plate as exemplified in reverse faulting processes.
Being constructive, the opposite is divergent boundaries where the two plates slide apart from each other in mid-ocean ridges and in oceanic or continental rifts.
Being constructive, the opposite is divergent boundaries where the two plates slide apart from each other in mid-ocean ridges and in oceanic or continental rifts.
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Plate Borders |
Transform boundaries witness two plates
grinding (not ‘sliding’ as is usually the misnomer description) past each other
as transform faults. When the relative motion appears left sided it is considered
sinistral and when moving right is said to be dextral. Transform boundaries are
conservative where much potential energy is stored as movement is locked up in
the uneven and serrated edge plate borders. Once the continual push for movement
by the locked plates finally overcomes the friction holding back motion, the
sudden release is known as an earthquake as is the case in the San Andreas
Fault line and its numerous tributaries.
Continental
Divide:
Continental drift driven by plate
tectonics always makes us think of Pangaea as the first continent mass, but
that assuredly was not the case. Composed of ancient crystalline basin rock, a
craton found in the interior of tectonic plates are very old and a stable
component of the continental lithosphere. Cratons are thick crustal portions of
the lithosphere sending lithospheric crustal roots deep into the mantle.
Essentially cratons are humongous rock cores formed from cooler mantle regions
and as insulated from magma melt permitted thick volcanic accumulations to
generate voluminous partial melt low density felsic rock. Felsic cratons first
appeared in the Archean Eon and lead to the first proto-continents.
Though much smaller than any of today’s continents, the first very probable small supercontinent to appear was Vaalbara ~ 3.35 bya. Vaalbara was once a whole craton that is now split with one half from the Kaapvaal region in southeastern Africa and the other half in Australia’s northwestern Pilbara region. Rock from both these regions is identical as once being from one craton source.
The small continent Ur was formed 3 bya,
but lingered hundreds of millions of years as Earth’s only continent surrounded
by a few micro islands. The whole continent of Ur survived intact even after
the new continent Pangaea engulfed it. Ur’s survival rate deems it as the oldest
living continent and perhaps so forever more. Ur’s current locations are
obscured in Australia, India and Madagascar.
Much larger than Vaalbara or Ur,
Kenorland formed around 2.7 bya. It comprised the core of present day Canada,
the United States and Greenland, today’s Scandinavia and Baltic region, western
Australia and the Kalahari Craton which is in the current desert of southern Africa. It
most likely floated along the equator.
The first true supercontinent with a
landmass roughly around 50 million square kilometers/19.305 million square
miles was Columbia. It existed from 1.8 bya to 1.5 bya and determined through
physical geological and paleomagnetic evidence encompassed the Ukrainian and Amazonian
Shields, Australia, Siberia, North China and the Kalahari Craton.
Existing between 1.1 billion-750 million
years ago (mya), the supercontinent Rodinia evolved out of the sheared and
dispersed pieces of Columbia along with new uplifted dry land masses. Columbia
remnants then merged with the newly formed craton and shield dry land masses to
form an enormous supercontinent that took up the majority of Earth’s surface
south of the equator.
Rodinia rifted apart into three continents
being proto-Laurasia, the Congo Craton and proto-Gondwana. Rodinia’s breakup is
critical to Earth’s historical course in its evolutionary sequencing. Up to
Rodinia’s existence, life was teeming in the oceans, but was all devoid on
land. The supercontinent’s breakup created much shallower oceans for that
transition to actually take place. Rodinia’s severing apart also created
extensive volcanism that fed the oceans and lands with super enriched mineral
nutrients.
There is some evidence that shows there
was a continent formed when proto-Laurasia rotated southward towards the South
Pole while proto-Gondwana rotated counterclockwise. In between the two
proto-continents, the Congo Craton drifted through causing some glancing
collisions creating a temporary supercontinent known as Pannotia 600 million
years ago. There was no true emergence of the continents and by 540 mya, the
short-lived Pannotia of 60 million years disintegrated into the four continents
Laurentia, Gondwana, Siberia and Baltica. But with so much landmass around the
South Pole, Pannotia left its indelible mark in evidence showing the most
extensive glaciation Earth has ever experienced.
Finally, the supercontinent Pangaea was
formed when the continents Laurasia, Gondwana, Siberia and Baltica merged
together 300 mya. Much evidence has been gathered on the existence of Pangaea
from lack of diversity in fossil evidence as life had already occurred on land
by this time and oceans were not separating species enough to diverge through
natural selection. Shared paleomagnetic minerals, matching geological trends
between the eastern coastline of South America and the western coastline of
Africa and matching glacial till found on the current continents that
identically match verifies an original source.
With three major phases in the rifting
apart of Pangaea, the first phase began 175 mya when Pangaea began rifting from
the Tethys Ocean opening up the North Atlantic and later the South Atlantic
forming the Atlantic Ocean. The southwest portion of the Indian Ocean opened up
separating Madagascar from India and supplanting it on the African plate
marginally as an island adjacent to East Africa.
The second major rift phase occurred on
average 145 mya splitting Gondwana into multiple continents known now as India,
Antarctica, Australia, Africa and South America. A subduction zone known as the
Tethyan Trench, sucked in the Tethyan mid-ocean ridge that was once responsible
for the broadening of the Tethys Ocean’s expansion. The subduction zone also
pushes Australia, Africa and India northwards. South America and Africa
separate.
The final third phase occurs 65-50 mya and
splits Laurasia into halves separating Greenland and North America (together
known as Laurentia) from Eurasia creating the Norwegian Sea. India began
colliding with the Asian continent 35 mya forming the Himalayan orogeny and
closing off the Tethys seaway. The Himalayan mountain system is still going on
today along with the rifting in the Red Sea Rift and East African Rift.
Geologic history bears out that supercontinent emergence and separation is cyclical occurring roughly every 250 million years. Below is a video that reconstructs the forming of continents from the remnants of Rodinia 400 million years ago to the supercontinent Pangaea, Pangea’s deconstruct to the present and continues constructing a possible model in the future 250 million years from now. It is interesting to watch.
As man moved into earthquake zones and
volcano regions along plate boundary lines, when the ultimate happens we
viscerally complain how cruel Mother Nature can be. For sure the immediate
impact is heart wrenching as a 7+ Richter scale earthquake has the potential to
wipe out 300,000 lives in an instant. But in the long run outlook, this renewal
and recycling of Earth material is a main reason that we as a species are here
today to even choose whether to live near a hazardous plate border or not…
Wet
& Airy World:
During most of the Hadean Eon,
primordial Earth was smaller but building in mass due to the heavy bombardment
periods. Water molecule vapors and the original hydrogen and helium atmosphere
would have escaped Earth’s gravity and atmosphere leaking out into space. The
Theia impact vaporized rock sending it into the atmosphere where it condensed
with the solids falling back to Earth within 2,000 years. This left behind the
hot volatiles in the atmosphere which resulted in heavy carbon dioxide and
water vapor measurements that had originally escaped as steam billowing out
from inside Earth.
~ 4.2 bya nearing the end of the Hadean
Eon there was a cooling off period for several 100 million years. This was due
to the original planetary accretion period’s heat dissipating with a period of
a much lessened influx of bolides. Bolides are simply meteoroids and asteroids
with an apparent magnitude > -7 in brightness and are enough in mass to
leave craters on impact. The onslaught of comet and hydrated asteroids brought about
half of Earth’s water adding to the amount that was originally trapped during
protoplanetary building, but the lack of their impacts allowed heated water vapor
to cool, condense and fall down to Earth. And raining down it did for thousands
of consecutive years forming the oceans.
Gradual leakage of water in hydrous
minerals occurred at a great extent during the earth’s cooling from a molten
state and still occurs at some degree today. The Earth’s surface still at 110 °C/230
°F during the cool off was not enough to offset liquid water into vapor states due
to the high atmospheric pressure of carbon dioxide remaining in the
atmosphere.
Crustal formation is much like the core/mantle
formation where the lighter silicate material formed higher altitude land
features and the heavier basaltic material sunk forming huge basins. With plate
tectonics kicking in, orogeny had begun in uplifting further the continental
land masses, while condensation began filling in the basins. Zircon crystal
studies bear out liquid water had been collecting on the surface as far back as
4.4 bya.
By the time the Archaen Eon had come 4
bya, oceans had formed but were acidic. This was due to the amount of carbon
dioxide filling the atmosphere where: CO2 + H2O ═> H2CO3
(carbonic acid). Carbon dioxide was also being pulled from the atmosphere by
the crustal portion of the lithosphere under water forming calcium carbonate: H2CO3
+ Ca++ ═> CaCO3
(limestone).
Fresh rock rich in calcium provided from
plate collisions became a storage reservoir of carbon dioxide by depleting it
from the atmosphere and utilizing the gas as a sink in sediment building. Due
to this, over the last 200 million years atmospheric carbon dioxide
concentrations have dropped.
Sea water as salty came about due to the
nature of pure water and the chemistry of minerals that dissolve in it.
Dissolved seawater solids originated from two key sources. Erosion and chemical
weathering of rock on land was transported out to the oceans by rivers and
their tributaries. The earth’s interior has also contributed to oceanic water
solid content by means of hydrothermal vents. Also, volcanism spews particulate
matter up into the atmosphere that eventually is carried down to the oceans by
precipitation (rain, snow), down winds or gravity. Although virtually every
element can be found dissolved in seawater, only six ions compose over 98% of
solids. Of those six ions, sodium and chloride account for 85%, which is why
seawater tastes like the sprinkled salt on your tomato.
Analysis of 4 billion year old Acasta
Gneiss from the Slave Craton in the Northwest Territories of Canada validate
that oceans and continents had formed prior to the Archean, but by the midterm
of the Archean Eon, Earth had an established atmosphere and ocean. Continental
land masses also had running water as shown from direct evidence of Greenland’s
3.8 billion year old sedimentary rock deposited and laid down as layered
sediment from running water. The hydrologic and sedimentary cycles were in
place by the early Archean.
As viewed from above though, the Archean
Earth would not appear as oceans of blue with white clouds dispersed in the
atmosphere. With turbid waters, the oceans would’ve been gray underneath a red
tinted sky due to the then composition of the atmospheric gaseous makeup and
percentiles of each. Though virtually no mountain orogeny or volcanoes exist
today from extensive Archean volcanism, remnants of this eon’s volcanism can be
studied from mostly flat continental cratons.
The extensive Archean volcanos spewed
out vast amounts of water steam, carbon dioxide, sulfur dioxide and a fair
amount of methane and hydrogen sulfide that along with the free nitrogen, became
the bulk of the eon’s atmosphere. Methane droplets suspended in air shrouded
the earth in that reddish tint global haze. No more than 3% of the atmosphere
contained oxygen as most free oxygen had been taken up into compounding water.
Grain analysis from rock formed during the Archean show a reducing atmosphere
and not an oxidative state that was to first appear at the very end of the
Archean.
In ending this segment with a paradox, 3
bya the young sun was only 70% as bright in magnitude as it is today and Earth
should’ve frozen snuffing out any chance for life to grab a foothold, but there
was no freezing. Why? Because at this time methane and carbon dioxide levels
were up to 10-200 times more per unit concentrate than they are today. These
greenhouse gases trapped enough of the sun’s heat to keep the Earth’s surface
temperatures above freezing. Food for today’s thought.
RNA
World:
After the oceans and atmosphere were
forming between the Hadean and Archean boundary, great amounts of carbon
dioxide was taken out of the atmosphere and locked up into carbonate sediment
by the vastly growing, but no less efficient ocean waters. Though there was an
appreciable amount of methane left, this left mostly nitrogen as the bulk of
atmospheric gas.
Today, cells within a living body
require basically three functions. One is the concentration of monomers,
enzymes and proteins to act as a wholesale energy source. They also require the
removal of free oxygen and hydroxyl radicals as waste. Thirdly, access to
prebiotic or biotic monomers to form genetic polymers existing in a steady
state but far from equilibrium is key to existing life. How did all this come
about? Let’s attempt to describe the sequence.
Rapid chemical synthesis of available
raw materials in the atmosphere begin producing amino acids, which are strictly
what they state they are…a compound containing an amino group (-NH3)
and a carboxylic acid group (-COOH). All naturally occurring amino acids have a
mirror left/right image. Known as enantiomers, these mirror images though are
not identical, but because they can form as two distinct mirror images around a
central carbon atom, they all, except for glycine, occur in two isomeric forms.
This is due to the lack of plane symmetry in the amino acids, so in effect are
stereoisomers as opposed to mono. These isomeric forms are called L and D
analogous to left handed and right handed configurations.
Both L-amino acid and D-amino acid
stereoisomers have been found in meteorites, which surely brought them to Earth
during the early bombardments, but only L is utilized in any organism’s
synthesis of proteins, where D-amino acids are relegated to minor functionary
roles such as membranous wall building. However, D-amino acids later become
vital to nucleic acid as DNA having D-ribose sugars.
The synthesis of available chemicals
into amino acids and the borrowing of amino acids from bolide contributions
gave the existing oceans’ monomers a foundation to build from. Mono means one
and mer is a structural unit, so monomer means one structural unit. Polymer
where poly means more than one needs to come about by monomers adhering or polymerizing
into repeated structural units.
During the Archean Eon we have soluble
amino acid monomers loosely mixed in solute with the existing oceanic waters. This
is important for the ocean waters protect the amino acids from UV photon
disruption and creates an ease of interaction pathways.
The gravitational tug of the sun/moon on
Earth’s oceanic tides creates zones of evaporate silicate clays along the
coastal shorelines. The clays’ valence charges collect the amino acids. Heat
from expelled lava warms the coastal waters. Tidal pools form concentrating the
amino acids. All this allows the concentrated amino acids to polymerize. Within
a range of 55-85 °C/131-185 °F, warmer waters were conducive to polymerization
of the amino acids into peptide chains. The silicate clays, favoring L-amino
acids act as a catalyst. The clays perfunctory role was acting as an adsorption
median to the activated amino acid monomers’ enhanced polymerization and did
this by increasing monomer concentration orienting them in favorable
condensation during the process. Even in thermodynamically unstable conditions,
kinetic traps, which define the rate at which a chemical reaction occurs, would
accelerate processes to produce chemical bonds between monomers.
As these organic peptide polymers
concentrate themselves, under lab conditions they separate out from the liquid
media they were suspended in as individual droplets. This leads to a proto-cell
(analogous and a precursor to, but not quite yet life) embroidered with long
chain molecules acting as a membrane allowing the proto-cell to become anhydrous.
Within the proto-cell, a monosaccharide (simple) sugar was trapped. This sugar
was ribose that was abundantly produced in an environment of UV, heat and
lightning synthesizing its abundant and basic building blocks of carbon,
hydrogen and the available free oxygen into the sugar’s chemical formula C5H10O5.
Efficacy of enzymes performing as
catalysts is far more efficient than simply clays with a silicate surface. The
common bond between all today’s biotic enzymes is centered on the primitive
pyridoxal phosphate dependent stabilization process of α-aminoacrylate or
α-aminocrotonate. As you can see from the figures below, both amino groups
either have a nitrogen or ammonium base which was readily available during the
Archean. Phosphate is an organic based molecular building block. So, the first
synthesized enzymes allowed an abiotic proto-cell membrane to catalyze basic
synthesis. It also may have led to deleterious synthesis erupting into a
metabolic state such as the product of indole condensation with
α-aminocrotonate. These first enzyme mutations were the precursors to genetic
mutations.
![]() |
Aminoacrylate |
![]() |
Aminocrotonate |
Amphiphiles, first brought to Earth by
meteorites are chemicals that possess both hydrophilic (water loving) and
lipophilic (fat loving) properties. This led to a transient complex that
allowed mixtures of amphiphilic molecules to enter osmotic membranes composing
a vesicle’s assemblage.
Large chains of amino acid residue began
forming a sequenced macromolecule that became a protein and with the amino
acids in sequence began replication. Higher levels of modified nucleotides
reached the threshold in the homogeneity required to produce nucleic acid. With ribose sharing duty with phosphate in serving
as a backbone, they bonded to the nucleotides adenine, cytosine, guanine and
uracil. Ribonucleic acid (RNA) had been polymerized with its first important
role in synthesizing proteins as enzymes. Further, an outreach of RNAs would
independently serve as a catalyst for chemical reactions. This class of RNAs is
designated as ribozymes and was just discovered in 1989 by Sidney Altman and
Thomas Cech earning them the Nobel Prize in chemistry.
A glorified ribozyme known as a ribosome
became a large molecular complex that assembles proteins to perform a vast
array of functions from reproducing RNA to responding to stimuli.
Most likely the original ribose sugar
was not in enough abundance to form long polymerase strands and there weren’t biotic
enzymes yet strong enough in efficacy to catalyze the long single strands.
However it has been verified through lab experiments that in the absence of
enzymatic catalysts, single stranded RNA can copy strands of itself through
template-directed polymerization. This process has been shown to be slow and
prone to error in which may have forced the proto-cell to come up with more
proper duplication, hence the process explained from the above two last paragraphs
evolved.
Also, lab trials have proven that long
strands of RNA can form in salty icy water. A dilute solution of chemically
activated RNA nucleotides causes nucleotide concentrations while ice crystals
are forming resulting in the formation of long strands of RNA.
With a culmination of a myriad of
chemical and geophysical processes, life had introduced itself on Earth.
Assuredly there was multiple trial and error periods with a frequent hit and
miss combination as life did not first appear until well after 100s of millions
of years had passed since the first oceans and atmospheres formed.
Once the proto-cell began replicating
itself, RNA as the precursor to DNA’s origins, life was introduced to Earth. As far back as we can go
through fossil records, life first formed 3.8 bya from the proto-cell as Archaea,
a microorganism no larger than 0.1 micrometers. Archaea have no morphology to
leave fossils, but they do leave chemical fossils of lipids unique only to
their kind. Very tiny in size as the first species of life, but was humongous
in size as the frontrunner to what life was to evolve into and out of.
Once
More:
So life began on Earth. Coming later,
the third segment of ‘Et Tunc Nulla Erat’ will begin to trace the evolutionary
tale of life.
The above episode of Earth’s geological
history was not expounded on. Each segment, even at times each paragraph could
have been only explained completely in book form. Hopefully some insight if not
some knowledge was gained here for the brave reader that read on through and
hopefully it might have spurred some interests.
You may have noted there were times
during your read that the name Earth was capitalized and at times it wasn’t.
Earth is a proper planetary name and as in all planet names, such as Venus or
Neptune it should be capitalized. But for the mere fact Earth is used much,
much more from technical papers to laymen editorial excerpts, we have forgiven
those that do not capitalize Earth, but only after it is followed by the word
‘the.’ So, Earth is Ok, but the earth is also okay as well.
The video below is not an in depth recap,
but does tie a few things together that was discussed in this article.
Signed but not
Sealed,
BJA
Nov. 09-10, 2013
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