BSCI 10001 Lecture Notes - Lecture 1: Mesozoic
SchoolKent State University
Course CodeBSCI 10001
ProfessorAdam Arthur Leff
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As you well know, water (H20) is a molecule made of two hydrogen atoms plus one oxygen
Atoms have a nucleus with positively charged protons (plus in all cases except hydrogen, some
neutrons), orbited by negatively charged electrons:
So now let me ask you: Where do all these 112 different kinds of atoms (the elements listed in
the Periodic Table) come from?
They were all made long ago inside stars.
All the different elements that make up the material in the furniture in this room; the room
itself, and all the different kinds of atoms that make up your bodies: all of this was created
billions of years ago in the furnace of stars that existed at an earlier time in our galaxy, long
before our own star (the sun) was formed.
In the center of stars, the huge force of gravity compresses hydrogen nuclei (protons) so tightly
together that they begin to fuse to form helium nuclei. 4 protons fuse to form a helium
Our sun is fusing (“burning”) hydrogen to make helium, and will continue doing so for about
another 5 billion years. Basically, our sun is a long, continuous, sustained hydrogen bomb
The energy released in the center of the star by the fusion of hydrogen nuclei to form helium
provides an outward force that counteracts the inward force of contraction due to gravity.
Consequently, once ‘ignition’ has occurred, the star remains at a more or less constant size over
time, as long as it is ‘burning hydrogen.'
As our sun synthesizes helium, this helium accum-ulates in the center of our sun.
Stars bigger than our sun (10x bigger) follow a different fate. After forming carbon, large stars
will successively form neon, then oxygen, silicon, and finally iron:
When all the silicon is depleted, then there is no more fusion-released energy to stave off the
gravitational collapse of the star. The star collapses, and then explodes outwards. This is called
a “Super Nova”:
(In the case of stars of size between 10 and 25 times the mass of our sun, the residue left after
a supernova explosion consists of close-packed neutrons; it is called a neutron star; with stars
of mass greater than 25x that of our sun, the neutrons collapse in the face of the huge
gravitational field and a Black Hole forms after the supernova event.)
The huge energies associated with supernova explosions result in the synthesis of all the rest
of the elements in the periodic table.
The cloud of elements blown out into space as “cosmic dust” after a nova event is called a
The “cosmic dust” from supernovas can then collapse again gravitationally to form new second
generation suns with planetary systems like ours. All the elements like iron, silicon, carbon,
oxygen, silver and gold we find on our planet were made in a sun many billions of years ago.
Our planet, and we ourselves, are literally made of “stardust.”
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