elemental classes.pptx in a geochemistry

Classification of Elements
Dr. Anwar Qadir
The University of Haripur

Geochemistry - an Introduction
What is Geochemistry?
The urge to make geology more quantitative has led to the widespread
inclusion of the so-called “basic” sciences such as physics and chemistry into
the study of geology. The term “geochemistry” was first used by the Swiss
chemist Schönbein in 1838. V.M. Goldschmidt, who is regarded as the
founder of modern geochemistry, characterized geochemistry in 1933 with
the following words:
“The major task of geochemistry is to investigate the composition of the Earth
as a whole and of its various components and to uncover the laws that
control the distribution of the various elements. To solve these problems, the
geochemist needs a comprehensive collection of analytical data of terrestrial
material, i.e. rocks, waters and atmosphere. Furthermore, he uses analyses
of meteorites, astrophysical data about the composition of other cosmic
bodies and geophysical data about the nature of the Earth’s inside. Much
useful information also came from the synthesis of minerals in the lab and
from the observation of their mode of formation and stability conditions.”

Definition and Sub-disciplines
Geochemistry uses the tools of chemistry to understand processes on
Earth.
 Trace element geochemistry
 Isotope geochemistry
 Petrochemistry
 Soil geochemistry
 Sediment geochemistry
 Marine geochemistry
 Atmospheric geochemistry
 Planetary geochemistry and Cosmochemistry
 Geochemical thermodynamics and kinetics
 Aquatic chemistry
 Inorganic geochemistry
 Organic geochemistry
 Biogeochemistry
 Environmental geochemistry
 …
The wide field of Geochemistry includes:

The Periodic Table of Elements

Isotopes
The atoms of an element can differ in
mass from each other because they
have differing numbers of neutrons.
Those with more neutrons will weigh
more and be more massive. The
atomic mass (often referred to as
atomic weight) of an element is
calculated by adding together the
number of protons and the number of
neutrons.
Examples for isotopic couples:
Stable isotopes:
H-1, H-2 (D), H-3 (T) (or 1
H, 2
H, 3
H)
C-12, C-13, C-14 (or 12
C, 13
C, 14
C)
O-16, O-18
Radiogenic isotopes:
Fe-54, Fe-56
U-235, U-238
The Periodic Table of Elements
Symbols and numbers

Electrons and Orbits
The electronic structure of
an atom largely determines
the chemical properties of
the element.
Elements within the same
group of the Periodic Table
have the similar outer
electronic configuration and
behave chemically similar.
Each electron shell
corresponds to a period or
row in the Periodic Table.
The periodic nature of
chemical properties reflects
the filling of successive
shells with additional
electrons.
The Electronic Structure of Atoms

The Electronic Structure of Atoms
Electron shell representation of
carbon atom:
The inner-most (first) shell is full as it
can hold only two electrons. The second
shell can hold eight but has only four.
Protons, neutrons, electrons
K shell
L shell
The copper atom has one lone
electron in its outer shell, which can
easily be pulled away from the atom.
K
N
M
L

The Electronic Configuration of the Elements

Chemical Properties of the Elements
Ionization potential
The First Ionization
Potential is the energy
required to remove the
least tightly bound
electron from the atom.
Example: H --> H+
+ e-
The second, third, …
ionization potentials are
defined
correspondingly.
Valence is the number
of electrons given up or
accepted. Transition
metals often have more
than one valence.
Example: Fe(II) and
Fe(III)

Electron Affinity
Electron Affinity is a measure of the desire or ability of an atom to gain electrons. It is an
energy concept. The formal definition states that Electron Affinity is the amount of energy
released when an electron as added to an atom. Most atoms tend to lose energy when they
gain electrons. Some atoms do not. The elements located in the upper right corner of the
Periodic Chart have the high E.A. values (usually found as anions ) while those in the lower
left corner have the low E.A. value (usually found as cations ). A generic equation of the EA
process would be as follows.
X + e-
--> X-1
+ EA. Often this is measured in electronvolts.
Electronegativity
The concept of Electronegativity refers to the ability of a bonded atom to pull electrons
towards itself.
It is defined as the relative ability of an atom in a molecule to attract electrons towards itself.
As atoms bond, electrons are shared or transferred. The atom with the higher
electronegativity will dominate the electrons.
In order to be able to determine electronegativity values it is important to observe the
behavior of atoms in a bonded situation. Consequently, the Noble Gases do not usually
appear with listed electronegativity values.

Pauling Scale
The Pauling Scale is the most commonly used scale of electronegativity values. The
calculations used to arrive at the numbers in the scale are complex. It is most common to
simply know the results of those calculations. The scale is based on Fluorine having the
largest electronegativity with a value of 4.0. The Francium atom is assigned the lowest
electronegativity value at 0.7. All other values are located between these extremes.
Examples: Li--1.0 Be--1.5 B--2.0 C--2.5 N--3.0 O--3.5 F--4.0.
(Pauling scale)

R.S. Mulliken (1934) proposed an electronegativity scale in which the electronegativity, M
is related to the electron affinity EAv (a measure of the tendency of an atom to form a
negative species) and the ionization potential IEv (a measure of the tendency of an atom to
form a positive species) by the equation:
M = (IEv + EAv)/2
The subscript v denotes a specific valence state.
The Mulliken electronegativities are expressed directly in energy units, usually electron volts.

Ionic radius
Cations have smaller radii than anions. Ionic radius decreases with increasing charge.
Ionic radius is important for geochemical reactions such as substitution in crystal lattices,
solubility, and diffusion rates.
Comparison of some atomic and respective ionic
radii (in nanometers)

Chemical Bonding
Ionic Bond: total transfer of electrons from one atom to another
Covalent Bond: the outer electrons of
the bound atoms are in hybrid orbits that
encompass both atoms.
Due to different electronegativity, covalent
bonds are often polar --> dipole
interactions (Van der Waals interactions)

Chemical Bonding
Metallic Bond: valence electrons are not
associated with any single atom, but are
mobile (“electron sea”).
This bond type is less important in
geochemistry than the other bonds.

Chemical Properties of the Elements - Summary
Hydrogen Hydrogen is unique as it is the simplest possible atom consisting of
just one proton and one electron
Alkali Metals These are very reactive metals that do not occur freely in nature.
These metals have only one electron in their outer shell, therefore
they are ready to lose that one electron in ionic bonding with other
elements. The alkali metals are softer than most other metals.
Cesium and francium are the most reactive elements in this group.
Alkaline Earth
Metals
The alkaline earth elements are metallic. All alkaline earth elements
have an oxidation number of +2, making them very reactive.
Because of their reactivity, the alkaline metals are not found free in
nature.
Transition
Metals
The transition elements are both ductile and malleable, and conduct
electricity and heat. The interesting thing about transition metals is
that their valence electrons, or the electrons they use to combine
with other elements, are present in more than one shell. This is the
reason why they often exhibit several common oxidation states.
Other Metals The 7 elements classified as other metals, unlike the transition
elements, do not exhibit variable oxidation states, and their valence
electrons are only present in their outer shell. All of these elements
are solid. They have oxidation numbers of +3, +4, -4, and -3.

Chemical Properties of the Elements - Summary
Metalloids Metalloids are the elements found along the stair-step line that
distinguishes metals from non-metals. This line is drawn from
between Boron and Aluminum to the border between Polonium and
Astatine. Metalloids have properties of both metals and non-metals.
Some of the metalloids, such as silicon and germanium, are semi-
conductors.
Non-Metals Non-metals are not able to conduct electricity or heat very well. As
opposed to metals, non-metallic elements are very brittle. The non-
metals exist in two of the three states of matter at room temperature:
gases (such as oxygen) and solids (such as carbon). They have
oxidation numbers of +4, -4, -3, and -2.
Rare Earth
Metals
The thirty rare earth elements are composed of the lanthanide and
actinide series. They are transition metals. One element of the
lanthanide series and most of the elements in the actinide series are
called trans-uranic, and are synthetic or man-made
Halogens The term Ò
halogenÓmeans Ò
salt-formerÓand compounds containing
halogens are called Òs
altsÓ.All halogens have 7 electrons in their
outer shell, giving them an oxidation number of -1. The halogens are
non-metallic and exist, at room temperature, in all three states of
matter
Noble Gases All noble gases have the maximum number of electrons possible in
their outer shell (2 for Helium, 8 for all others), making them stable
and preventing them from forming compounds readily.

What is the Solar System made of?
What is the relative abundances of the various elements throughout the Universe?
This turns out to be a difficult task for one obvious reason. Spectroscopic measurements
of elements from the distant stars are strongly biased towards only those elements in
excited states at or near the stellar surface. Those elements principally in the interior do
not contribute to surface radiation in the same proportions as actually exist in a star.
The situation is better for the Sun. When element distributions are stated as Cosmic
Abundances, they actually are rough estimates made from Solar Abundances .

What is the Solar
System made of?
From the figure, we see four
patterns:
 An overwhelming abundance
of light elements
 A strong preference for even-
numbered elements
 A peak in abundance at iron,
followed by a steady decrease.
 Elements 3-5, Lithium,
Beryllium and Boron, are very
low in abundance.
These patterns have to do with
nucleosynthesis (element
formation) in the stars.

What is the Solar System made of?
If the Sun and Solar
System formed from the
same material, we would
expect the raw material of
the planets to match the
composition of the Sun,
minus those elements that
would remain as gases.
We find such a
composition in a class of
meteorites called
chondrites, which are
thought to be the most
primitive remaining solar
system material.
Chondrites are considered
the raw material of the
inner Solar System and
probably reflect the bulk
composition of the Earth.

What is the Earth
made of?
Relative abundance by weight
of elements in the whole
Earth and in the Earth’s crust.
Differentiation has created a
light crust depleted in iron
and enriched in oxygen,
silicon, aluminum, calcium,
potassium, and sodium.

What is the Earth made of?
Crustal Element Distribution
The abundance of elements in the Earth's crust is much different from the abundance of
elements that are to be found on the other planets and our Sun. The continental crust of
the Earth also differs radically from the overall composition of the Earth.
Our Earth as a whole and its crust, in particular, have extraordinary concentrations of
elements, all associated with silicate minerals like olivine, pyroxene, amphibole,
plagioclase, the micas, and quartz. Although there are a vast number of silicate minerals,
most silicate minerals are made from just eight elements.
The two most common elements in the Earth's crust, oxygen and silicon, combine to form
the "backbone" of the silicate minerals, along with, occasionally, aluminum and iron.
These four elements alone account for about 87% of the Earth's crust. This silicate or
alumina-silicate "backbone" carries excess negative charge, however. Positive charge in
the form of cations has to be brought in to balance this negative charge. The four most
important elements that fit in the mineralogical structures of the silicates are calcium,
sodium, potassium and magnesium. Taken all together, constituting nearly 99% of crustal
elements, leaves little room for all of the other elements.
As a consequence, all other elements are either nearly absent from the Earth's crust or
are found primarily in non-silicate rocks.

elemental classes.pptx in a geochemistry

Cosmochemistry
• Nucleosynthesis
• The origin of elements
• Information come from meteorites and stars
• The universe began 10 to 20 Ga with a Big Bang
• The universe is cooling, expanding and evolving
• Two posssibilities for the origin of elements
• 1. with big bang
• 2. after the big bang
• Elements H and He were created during the Big Bang
• Whereas elements heavier than Li were created after the Big
Bang
•
Origins of the Universe 101
| National Geographic - You
Tube

https://www.youtube.com/watch?v=i_DBe-xYpts
https://www.youtube.com/watch?v=wgUIB4tD0cM

Assignment 1
The process of nucleosynthesis (Origin of elements) and the
relationship with the formation of stars.
Due date 10-10-22

Polygenetic hypothesis
1. Cosmological nucleosynthesis
2. Stellar nucleosynthesis
3. Explosive nucleosynthesis
4. Galactic nucleosynthesis

The main points: Meteorites
• Each year Earth sweeps up ~80,000 tons of extraterrestrial
matter, from microscopic dust particles to large rocks
• Some are identifiable pieces of the Moon, Mars, or Vesta;
most are pieces of asteroids
• Meteorites were broken off their parent bodies 10’s to 100’s
of million years ago (recently compared to 4 Billion Years)
• Oldest meteorites (chondrites) contain bits of interstellar
dust, tiny diamonds made in supernova explosions, organic
molecules and amino acids (building blocks of life), tiny
spherules left over from the very early Solar System
• Direct insight into solar system formation

Meteor showers
• Time
exposure
image,
tracking
stellar motion
• Stars stay
still,
meteorites
make trails

Rocks Falling from the Sky
• Wikipedia
Meteoroid: chunk of debris in the Solar System.
Meteor: The visible path of a meteoroid that enters Earth's (or
another body's) atmosphere.
Meteorite: A meteoroid that reaches the ground and survives
impact
Meteor Shower: Many meteors appearing seconds or minutes
apart.
Origin: Comes from Greek meteōros, meaning "high in the air”.
• How can you tell that you have a meteorite?
– Higher metal content than terrestrial rocks
– Contain Iridium and other isotopes not in terrestrial rocks

What are meteorites?
• Chunks of rock or iron-nickel that fall to Earth from space
• Pieces of asteroids, comets, Moon, Mars, interstellar dust
– Can weigh from < 1 ounce to a few tons (!)
• “The Poor Man’s Space Probe”
– From parts of the Solar System astronauts may never explore
• Usually named after the place where they fall
– Examples: Prairie Dog Creek (US), Zagora (Morocco), Campo del
Cielo (Argentina), Mundrabilla (Australia)

What do meteorites look like?
Meteorite
from Mars
Allen Hills
(Moon)
Vesta

Variety of meteorite “falls”
• Tiny pieces of cosmic dust
– Collected by special airplanes, in clay under the
oceans, or in Antarctic ice
• Find single small chunks of rock
– Sometimes at random, sometimes by following
trajectory of a “fireball” or meteor trail
• A several-ton meteorite breaks up during
descent, falls as separate pieces
– Biggest pieces can make large craters if they hit land

Small particles: spherules
Spherule from Moon
Collected by Apollo 11 astronauts
• Tiny droplets from space
• Formed by melting and re-solidification after impacts
Spherule
from bottom of the Indian Ocean

Small particles: cosmic dust
• Sometimes from comets, sometimes left over from the
cosmic dust cloud from which the Solar System formed

Single small chunks of rock
Iron-nickel meteorite
A few inches across Allende
Carbonaceous chondrite

Several-ton boulders
Hoba Meteorite, Namibia

Worldwide frequency of meteorites
as function of size
Impact Frequency
Size Frequency Destruction Area
Pea 10/ hour
Walnut 1/ hour
Grapefruit 1/ 10 hours
Basketball 1/ month
50 meters 1/ century New York City
1 kilometer 1/ 100,000 years Virginia
2 kilometers 1/ 500,000 years France
10 kilometers 1/ 100 million years World-Wide?

The Great Daylight Fireball of 1972
• Skipped thru Earth’s atmosphere at shallow
angle, then exited again into space
• About 10-m diameter, moving at 15 km/sec
(33,000 MPH).
• If it had hit the surface of the Earth, it would
have had H-bomb equivalent impact energy.
• http://www.youtube.com/watch?
v=dKiwzLFzQfc&feature=related

1908 Tonguska meteorite in Siberia
caused widespread devastation
• Fortunately it hit in an unpopulated area!

How meteorites are found
• Random “finds” lying on ground
• Fragments around meteor craters
• Follow glowing trail of meteor or fireball
• Systematic searches in Antarctica
• Special high-flying airplanes (for dust)

Random “finds”
• Rare: a big meteorite in desert of Oman
• Pretty rare: random “finds” of smaller chunks

Fragments around meteor craters
• Very large meteorites vaporize when they hit ground,
form big craters
• Sometimes small pieces are found around crater
Barringer Crater, Arizona

The Peekskill (NY) Fireball

Last year in Sudan....
• Link to Scientific American article

University of Khartoum students
did systematic search
• 45 students and staff of the University of
Khartoum rode buses out to desert, searched
in long lines. Found more than 280 pieces.

P Jenniskens et al. Nature 458, 485-488
(2009)
Macroscopic features of the Almahata Sitta
meteorite.

Systematic searches in Antarctica

Searching for rare meteorites
amidst thousands of Earth-rocks

Primitive vs. processed meteorites
• primitive
• about 4.6 billion years old
• accreted in the Solar
nebula
• processed
• younger than 4.6 billion
years
• matter has differentiated
• fragments of a larger object
which processed the
original Solar nebula
material
Based on composition, meteorites fall into two basic categories:

Origin of Meteorites
• Primitive meteorites condensed and accreted directly
from the Solar nebula.
• the stony ones formed closer than 3 AU from the Sun
• the Carbon-rich ones formed beyond 3 AU from the Sun, where
it was cold enough for Carbon compounds to condense
• Processed meteorites come from large objects in the
inner Solar System.
• the metallic ones are fragments of the cores of asteroids which
were shattered in collisions
• the rocky ones were chipped off the surfaces of asteroids,
Mars, and the Moon by impacts

Main types of meteorites
• Chondrites
– Carbonaceous
– Non-carbonaceous
• Achondrites
• Iron
• Stony-Iron

Chondrites
• Rocky, inhomogeneous, contain round
“chondrules”
Microscope
image

Carbonaceous Chondrites contain
complex organic molecules
• Amino acids, fatty acids,
other so-called “building
blocks of life”
• Did building blocks of life
come to Earth from space?
• Did life itself come to Earth
from space?
– “Panspermia” theory

Carbonaceous Chondrites: Insights
into Planet Formation?
• The oldest meteorites; quite rare
• Chondrules (round): primitive chunks of early
Solar System
• Calcium aluminum inclusions (CaI’s): isotope
ratios (26 Al and 26 Mg) suggest that a
supernova explosion went off right next to the
early Solar Nebula
– Did the supernova stimulate formation of our Solar
System?

Some types of Chondrites were formed
all at once: from one asteroid breakup

Iron meteorites
• Made of iron and nickel
• Pits made during atmospheric entry (hot!)

Iron meteorites: from core of
differentiated asteroids

The making of future meteorites!

Crystalization pattern of the iron is
unique
• Characteristic of very
slow cooling of iron
within an asteroid core
• Due to diffusion of
nickel atoms into solid
iron as core cools
• Says original asteroid
must have been large
enough to be
differentiated

Stony-Iron meteorites - the prettiest
• Crystals of olivene (a rock mineral) embedded in iron
• From boundary between core and mantle of large
asteroids?

Achondrites: from Mars and Moon
• From Mars:
– Tiny inclusions have same elements and isotope
ratios as Martian atmosphere (measured by
spacecraft on Mars)
• From the Moon:
– Astronauts brought back rocks from several regions
on the Moon
– Some achondrites match these rock types exactly

Where do meteorites come from,
and how do we know?
• Spectra: reflection of sunlight as function of
wavelength of light
• Spectra of some meteorites identical to some asteroids
• Implies asteroid was parent body
Toro

The main points: Meteorites
• Each year the Earth sweeps up ~80,000 tons of extraterrestrial
matter
• Some are identifiable pieces of the Moon, Mars, or Vesta; most are
pieces of asteroids
• Meteorites were broken off their parent bodies 10’s to 100’s of
million years ago (recently compared to age of Solar System)
• Oldest meteorites (chondrites) contain interstellar dust, tiny
diamonds made in supernova explosions, organic molecules and
amino acids (building blocks of life)
• Direct insight into pre-solar system matter, solar system formation

The main points: Cosmic Collisions
• Cosmic collisions played major role in Solar System evolution
– Aggregation of planets from planetesimals
– Formation of Moon, tilt of Venus’ and Uranus’ rotation axes,
composition of Mercury
• Also played a major role in Earth’s evolution
– Tilt of axis
– Mass extinctions (dinosaurs, others)
• Collision history derived from crater patterns, isotope ratios
• Probability of global catastrophic impact event once every 100
million years
• Strong interest in tracking all Near-Earth Objects (NEO’s) that
might hit the Earth in the future

Role of cosmic collisions in
evolution of Solar System
• Early phase (4.5 billion yrs ago): planet formation
– Planetesimals collided or accreted to form larger pieces
• Formation of Moon by glancing collision with Earth
• Removal of most of Mercury’s crust by collision
• Collision made Venus rotate backwards
• Collision tipped Uranus onto its side (now rotates at 90 deg to
rotation axes of all other planets)
• “Late Heavy Bombardment” (~3.9 billion years ago) from Lunar
record
– First signs of life on Earth immediately followed “Late Heavy
Bombardment” period. Is there some sort of causal connection?

Early phase (4.5 billion yrs ago):
planet formation relies on collisions

Evidence that Moon formed as
result of a collision
• Earth has large iron core, but the moon does not
– Earth's iron had already drained into the core by the time of the giant
impact that formed the moon
• Debris blown out of both Earth and the impactor came from their
iron-depleted, rocky mantles
• Explains why mean density of Moon (3.3 grams/cm3
) is much less
than Earth (5.5 grams/cm3
)
• Moon has same oxygen isotope composition as the Earth
– Mars and meteorites from outer Solar System have different oxygen
isotope compositions
– Moon formed form material formed in Earth's neighborhood.

Formation of the Moon….
– Large planetesimal collides w/ Earth at glancing angle
– Removed material is from mantle of Earth

“Late Heavy Bombardment” of
Moon
• Evidence from Moon suggests impact rate was
1000 times higher 4 billion years ago than 3.8
billion years ago
• Heavy bombardment of Moon slowed down
about 3.8 billion years ago
• Similar evidence from Mercury, Mars

Evolution of the Moon’s Appearance
"Mare" are huge lava flows that came from fissures
in Moon’s crust 3.2-3.9 billion years ago. There are
similar flows on Earth (Siberia, India).
Even during heavy bombardment, a major impact only
occurred every few thousand years. Now they only
occur over tens or hundreds of millions of years (so the
lunar surface hasn’t changed too much).

Basins on Mercury, Moon, Mars

Earth experienced major collisions
as well
• But most craters got eroded away, subducted, or drowned
• A tour of craters on Earth:
Algeria Chad (Africa) from airplane

Earth’s craters
Clearwater, Canada Henbury, Australia

Earth’s craters, continued
New Quebec, Canada
Tswaing, South Africa

Arizona’s Meteor Crater, the most
famous example

Impact event created opening of
Chesapeake Bay
• 35 million yrs ago, 2 mi wide
• 56 mile-wide crater
• Drilling  mixed bits of
crystalline and melted rock
that can be dated, as well as
marine deposits, brine, etc
• Tidal waves 1000 ft high
Inundated area (in blue)

Giant impact 64 million years ago:
best idea for dinosaur extinction
• Chicxulub crater
north of Yucatan
peninsula, Mexico
• 180 km wide
• Dated to same
period as
extinctions at
Cretacious-Tertiary
boundary

Corroborating evidence: Iridium
layer
• Layer of enhanced
abundance of Iridium
found worldwide
• Dated to same time as
dinosaur impact
• Asteroids contain high
concentration of Iridium,
relative to Earth
• Ash on top of Iridium
(huge fires)

BBC News, 2002: Evidence for Late
Heavy Bombardment on Earth
OUR PLANET WAS BEATEN UP
• The first convincing evidence that the Earth was bombarded by a
devastating storm of meteoroids and asteroids four billion years ago
has been found in Earth's oldest rocks.
• Scientists have looked for clues in sedimentary rocks from Greenland
and Canada - the oldest on Earth - that date from the waning phases
of the Late Heavy Bombardment.
• Researchers from the University of Queensland, Australia, and the
University of Oxford, UK, say they have detected in these rocks the
chemical fingerprints of the meteorites left over from the Late Heavy
Bombardment - various types of tungsten atoms (tungsten isotopes)
that must be extraterrestrial.

Impact energies are very large!
Kinetic energy =
1
2
MV 2
where V is velocity of impactor
V is very large (estimate orbital speed around Earth) : 30 km/sec = 66,000 mph
M density volume 5
gm
cm3 volume
Volume of sphere 
4
3
r3

1
6
d3
where d is diameter
Combine :
Kinetic energy =
1
2
MV 2
=
d
1 meter




3
1019
gm cm2
/sec2
250
d
1 meter




3
tons of TNT
If diameter d = 200 meters, Kinetic Energy = 2 billion tons of TNT!
Note VERY strong dependence on size of impactor, d (Energy  d3
)
Credit: Bob O’Connell, U Virginia

Drastic effects of impact on a
terrestrial planet
• At “ground zero” rock, water, biomass are vaporized or melted
• Deeper rock is shock recrystallized (ultra high pressures) and
fractured
• Series of deep fractures form, lava from the interior may erupt
• Shockwaves obliterate life just outside of “ground zero”
• Earthquakes (and impact itself, if in ocean) generate giant waves
in oceans, wipe out coastal areas
• Friction in atmospheric dust generates widespread lightening
• Thick dust in atmosphere blots out sun for months or years
• Aerosols caused by eruptions and vaporization remain in
atmosphere for decades

Future extinctions might not be
limited to dinosaurs

Near Earth Objects: will Earth have
another collision soon?

There have been many impacts in
the past

• (1542) The Planets In Our Solar System
– YouTube
• (1542) The Formation of the Solar System in 6
minutes! (4K "Ultra HD") - YouTube

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