Elements
and their Origins
What is the Earth made out of
and where did it all come from?
Elements
What are these?
What is this?
Stars are formed out of hydrogen gas.
Hydrogen is the most abundant element in the universe.
When the universe formed,
almost all matter was
hydrogen, with some helium.
The Big Bang
Big Bang Nucleosynthesis
Both hydrogen and helium form as protons and neutrons
assemble from quarks and then begin to collide together
in the first 100 seconds the universe existed.
No elements heavier than helium form.
So where did the rest of the elements
come from?
Elements from Helium to
Carbon are formed by stellar
nuceleosynthesis (nuclear
fusion) in all stars.
Our sun is currently fusing
Hydrogen atoms into Helium
atoms, releasing heat as mass is
converted to energy.
When the Sun runs out of
Hydrogen, it will begin to fuse
Helium into Carbon.
Our sun is too small to burn
Carbon, so when it runs out of
Helium fusion will stop.
fusing hydrogen to helium
fusing
slowly
helium to cooling
carbon
Elements from Nitrogen to Iron are
formed by stellar nucleosynthesis
(atomic fusion) in high mass stars.
4
12
16
24
28
32
56
Iron cannot fuse in stars - it is the end of the
fusion process.
Elements heavier than iron
are produced when massive
stars go supernova.
Massive stars explode when
they run out of nuclear fuel
and their iron cores collapse
catastrophically and rebound
- a Supernova!
During a supernova atomic
nuclei in the exploding star
are bombarded by neutrons,
growing in mass to form
heavy elements.
Actual supernova
in a distant galaxy
Supernovae blast heavy
elements into interstellar
space.
New stars and solar systems like our own form from the
elemental debris of older dying stars.
Eagle Nebula
“We are all made of star stuff.”
- Carl Sagan
Our solar system began as a
nebula - a cloud of interstellar
dust and gas, predominantly
hydrogen and helium, but also
containing heavier elements from
nearby supernovae.
Condensing proto-Sun
and solar nebula
Elements present in the solar nebula combined to
form molecules. Molecules of solid matter began to
clump into larger and larger pieces, eventually
forming the planets.
The Great Nebula in Orion
Metals and Silicates
Hotter
Hydrogen, Helium, Ices
Cooler
Refractory
molecules
condense
Snow Line
Volatile
molecules
condense
The inner planets
formed
predominantly from
the most abundant
refractory elements:
Iron
Silicon
Magnesium
Sulfur
and their
oxides.
Early on, the Earth
melted, causing most
of the iron to sink to
form a metallic core.
The lighter oxides
separated to form a
rocky mantle and
crust.
We are not certain how the Earth acquired its
abundance of volatile compounds such as N2, CO2 and
H2O. One possibility is that volatiles were delivered to
the Earth from the outer solar system by comets and icy
asteroids.
Abundance of Elements in Earth’s Crust