Does Uranium 235 come from outer space?

Question

U235 has a half-life of 704 million years, considerably less than the age of the earth. Does this mean it is not of the earth?

Answer 1

all elements ultimately came from space - we are all star dust when it comes down to it.

A half life of 700 million years does not mean it came from outer space after the Earth was formed though - it just means it is decaying slowly . In the 6 billion years since the formation of Earth - the U 235 has undergone around 8 half lives so is 1/256 of the original mass.

Answer 2

Not of this planet.  All elements more massive than iron came from supernova explosions.

Answer 3

I think you've missed the point of a 'halflife'.

The halflife of an element is the time for the mass of the element to decrease by half following the relationship;

m = m(0) e^ (-kt)

Where k is the decay constant and the natural log of 2 divided by this gives the time period in which half of the elements mass will have decayed into other isotopes/elements.

Uranium is a 'heavy' element. Most elements are formed in stars, certianly all the elements above Fe (iron) are made in supernovea stars where the great gravitational pressures during the stars collasp provide the energy to bind that many protons and neutrons into a single atomic nuclus.

Uranium is formed in such an implosion of a star and so technically it does come from outer space. But that uranium has probally exsisted for much more than 4.5 billion years (age of the Earth) before becoming part of it in the formation of Earth.

That said the early Earth would have had more Uranium than today.

Answer 4

The 'Big Bang' gave rise to the helium and hydrogen in  our universe. Wikipedia comments, 'Primordial nucleo-synthesis took place just a few minutes after the Big Bang and is believed to be responsible for the formation of a heavier isotope of hydrogen known as deuterium (H-2 or D), the helium isotopes He-3 and He-4, and the lithium isotopes Li-6 and Li-7. In addition to these stable nuclei some unstable, or radioactive, isotopes were also produced during primordial nucleo-synthesis: tritium or H-3; beryllium-7 (Be-7), and beryllium-8 (Be-8). These unstable isotopes either decayed or fused with other nuclei to make one of the stable isotopes.'

As the primordial hydrogen and helium clumped, under gravitation, into the first stars, the process of nuclear fusion began to build up the elements (carbon, oxygen, nitrogen, ... , iron). However, it is not energetically favourable for stellar fusion to synthesise elements heavier than iron.

When these early stars reached the end of their core fusion cycles, some of them detonated in spectacular explosions known as supernovae. During a supernova, much of the outer star is ‘blown-off’ by (possibly) a shock wave of neutrinos. The rapidly expanding stellar gases are heated to in excess of 10^9 Kelvin. Isotopes of heavy nuclei, above and beyond uranium, are created by these cataclysmic explosions. Many of the isotopes of uranium (U235, U233,...,U238), and other actinides, are created in slightly different ratios to those we find today on earth.

Our solar system is about 4.5 billion years (or so) old and it was created by the collapse of a gas cloud that was seeded with ancient supernovae dust. Thus, our planet received a mixture of uranium isotopes as well as all of the other elementary isotopes that can be found on the earth. However, the original ratio of the uranium isotopes would have been richer in U235 than they are now, some 4.5 billion years later. U235 has a half-life of 7.1 x 10^8 years but U238 has a half-life of 4.5 x 10^9 years. This means, that, during the existence of the earth (4.5 billion years) the U235 abundance has reduced by 6.338 half-lives or a factor of about ‘1/64 th’ of the original amount! On the other hand, the U238 abundance has only passed through one half-life and so it is only at ‘1/2’ of its original abundance.

I should also add, that, U233 has a half-life of 1.6 x 10^5 years, U234 has a half-life of 2.5 x 10^5 years, U236 has a half-life of 2.4 x 10^7 years,  U237 has a half-life of 6.8 days, and U239 has a half-life of 23.5 mins!

Thus, to answer your question - U235 is not of this earth nor are any of the other elements and isotopes they are all ancient stardust!

Answer 5

no not at all.

U-235 as the name suggests is quite a heavy element,as it possesses 235 as the atomic number. Due to it's heavy nature it exhibits radioactive properties which gives it a long half life period. Moreover Uranium disintegration follows 1st order kinetics thus making its disintegration independent of initial concentration. All of this just leads us to the conclusion that although it has a half life of about 704 million years which is considerably less than the age of the earth on does not imply it is outer space matter but just suggests the fAct that it could have been one of the prime elements of the earth's crust at the time of it's formation and that it later transformed into other elements through nuclear fissioon.

Hope i've been helpful.

Answer 6

Most nuclear reactors use Uranium, which is commonly found on Earth. Uranium is actually formed in stars, but a large amount of it was believed to have settled on Earth during its formation. Uranium-238 is what makes up most of the worlds uranium supply (~99%). U-235 composes 0.7 of the worlds uranium supply, with much of the remaining uranium being U-234.

Uranium is a radioactive element that occurs naturally in varying but small amounts in soil, rocks, water, plants, animals and all human beings. It is the heaviest naturally occurring element, with an atomic number of 92. In its pure form, uranium is a silver-colored heavy metal that is nearly twice as dense as lead. In nature, uranium atoms exist as several isotopes, which are identified by the total number of protons and neutrons in the nucleus: uranium-238, uranium-235, and uranium-234. (Isotopes of an element have the same number of protons in the nucleus, but a different number of neutrons.) In a typical sample of natural uranium, most of the weight (99.27%) consists of atoms of uranium-238. About 0.72% of the weight consists of atoms of uranium-235, and a very small amount (0.0055% by weight) is uranium-234.

Small amounts of uranium are found almost everywhere in soil, rock, and water. However, concentrated deposits of uranium ores are found in just a few places, usually in hard rock or sandstone. These deposits are normally covered over with earth and vegetation. Uranium has been mined in Canada, the southwest United States, Australia, parts of Europe, the former Soviet Union, Namibia, South Africa, Niger and elsewhere.

Answer 7

Anything heavier then Iron can only be formed, in nature, by supernova.

The pressures and densities required can only be found in these intstellar explosions.

Answer 8

Having a longer half-life than the earth is old has nothing to do with existing longer. The half-life of a quantity whose value decreases with time is the interval required for the quantity to decay to half of its initial value.

Essentially, ALL elements came from outer space, its just helium fused together in the stars over millions of years or created in the hot fires of a billion super novae. Therefore it is normal for radioactive materials to have a longer half-life than the earth is old. And think urther: how about the other materials of the earth

Answer 9

U235

U-235 and U-238 occur naturally in nearly all rock, soil, and water. U-238 is the most abundant form in the environment. U-235 can be concentrated in a process called “enrichment,” making it suitable for use in nuclear reactors or weapons.

U235 more

http://www.bt.cdc.gov/radiation/isotopes...

Answer 10

What does half-life have to do with it?  It looks like you misunderstand the term.

If a clump uf U235 were formed today, then half of it would have "decayed" by 704 million years from now.  But the OTHER half of it would still remain.  In another 704 million years, half of the rest would have "decayed" leaving 1/4 of the total remaining after 1,408 million years

So U-235 could have been made when the earth was formed, and depending on the exact age of the earth there would be a significant amount of it still remaining.

Answer 11

the earth was 4.6 billion years old

uranium's half life is inside that age

uranium maybe present at outer space

but the earth also has it's own source