How do scientists know how old the Earth is?

Question

They estimate that it is 4.5 billion years old. I would like to know how did they get this figure? And also the same about the Sun?

Answer 1

AGE OF THE EARTH

Early estimates of the age of the earth, prior to the discovery of the radioactive decay of unstable isotopes of heavy elements to produce stable isotopes of lead, asked how long would it take for the earth to cool to its current temperature and worked on the assumption that there was no heat source, once separated from the sun, that would counteract that cooling. And were far too low.

But once radioactive decay of uranium and thorium was realised to release heat along with alpha particles, that picture and its result of about 100 million years had to be revised. The acceptance of Drawin's theories of evolution and natural selection argued for a much longer time scale than 100 million years, in any case.

Radiometric techniques are now used, based on the balance of various isotopes of lead (the ratio of Pb-207 to Pb-206 in particular) found in rocks, as a result of the radioactive decay chains of thorium and uranium, which lead to stable isotopes of lead and the age of the earth can then be calculated, in knowledge of the half-lives of each of the nucleides in the decay chains.

But which rocks to study?

Studies of the age of rocks on the earth's surtface tend to produce too low an estimate of its age, because of weathering, erosion and tectonic plate movement. Also, past volcanic activity may have produced lava from the earth's core on the surface, to confuse the picture.

Therefore preference has been given to meteorites (rocks from space large enough to descend to the earth's surface without being burned up in the upper atmosphere) in particular the large Canyon Diablo meteorite which impacted at Barringer Crater, Arizona and is known from fragments collected around the crater and nearby Canyon Diablo which lies about 3 to 4 miles west of the crater. The meteorite is an iron octahedrite which fell between 20,000 and 40,000 years ago.

Clair Cameron Patterson, in 1953, used samples of the meteorite to measure the age of the Earth at 4,550 million years (± 70 million years).

The Canyon Diablo date has been backed up by hundreds of other dates, from both terrestrial samples and other meteorites. The meteorite samples, however, show a spread from 4.53 to 4.58 billion years ago. This is interpreted as the duration of formation of the solar nebula and its collapse into the solar disk to form the sun and the planets. This 50 million year time span allows for accretion of the planets from the original solar dust and meteorites.

The moon as another extraterrestrial body which has not undergone plate tectonics and which has no atmosphere, and therefore no weathering, provides quite precise age dates from the samples returned from the Apollo missions. Rocks returned from the moon have been dated at a maximum of around 4.4 and 4.5 billion years old. Martian meteorites which have landed upon the Earth, have also been dated to around 4.5 billion years old by lead-lead dating.

Altogether the concordance of age dates of both the earliest terrestrial lead reservoirs and all other reservoirs within the solar system found to date are used to support the hypothesis that the Earth and the rest of the solar system formed at around 4.53 to 4.58 billion years ago.

Independent verification of radiometric date of meteorites can be accomplished using studies of the sun. The sun can be dated using "helioseismic" methods which strongly agree with the radiometric dates found for the oldest meteorites.

Helioseismology is the study of the propagation of pressure waves in the Sun. Solar pressure waves are generated by the turbulence in the convection zone, near the surface of the sun and the acoustic waves are transmitted to the outer photosphere of the sun, which is where the light emitted by the sun is generated.

The acoustic oscillations are best observed by measuring the doppler shift of photospheric emission lines. Changes in the propagation of pressure waves through the Sun reveal inner structures and allows astrophysicists to develop extremely detailed profiles of the interior conditions of the Sun.

AGE OF THE SUN

The Sun's current age, determined using computer models of stellar evolution and nucleocosmochronology, is thought to be about 4.57 billion years.

The Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than 4 million tonnes of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation. The Sun will spend a total of approximately 10 billion years as a main sequence star.

Nucleocosmochronology is a relatively new technique used to determine timescales for astrophysical objects and events. This technique employs the abundances of radioactive nuclides in a way that is very similar to the use of C14 in dating archaeological samples, save that the elements measured are typically uranium and thorium.

Nucleocosmochronology has already been successfully employed to determine the age of the Sun (4.57±0.02 Ga, where Ga stands for giga-year, i.e., 109 years) and of the Galactic thin disk (8.3±1.8 Ga), among others. It has also been used to estimate the age of the Milky Way itself,

Answer 2

The base assumption is the entire solar system is a pool of matter before it started to break apart into individual objects. So all objects in the solar system are formed at the same time and thus have the same age. Scientists are unable to determine the EXACT age of Earth using radiometric dating of rocks on Earth because the primordial rocks are recycled or destroyed by plate tectonics. However, since all objects in the solar system are of the same age, scientists could use rocks from other objects which do not experience plate tectonics, such as meteorite and rocks on moon. A small number of rocks from moon collected by 6 Apollos and 3 Luna missions and more than 70 meteorites are used in radiometric dating. The determined age is between 4.53 and 4.58 billion years. To obtain the best age for earth, earth and the meteorites are considered as an evolving system. The ratio of Pb-207 to Pb-206 is then studied and compared to the oldest lead ores on Earth. Since we know uranium decays into lead and how long this process takes place, we can estimate the age of Earth to 4.54 billion years with 1% uncertainty. This age represents the last time lead was uniformly distributed throughout the solar system (which was a pool of matter that time before solid objects like planets formed).

Answer 3

Scientists are able to date the earth by using radioactive dating. What scientists do is take rocks and compare the number of radioactive isoptopes of a certain element in the rock with the number of nonradioactive isotopes of the same element. This will determine how many half lives the radioactive element has undegone because we know what the initial amount of the radioactive isotope that should have been present in the rock. The half-life of the radioactive isotopes used for dating are known. So once you know how many half lives have occurred you multiply that number by the half life of the isotope. This gives the age of the rock. Scientists have looked at many rocks and geologically know where the oldest rocks are. To date the oldest rocks give a date on the order of 4 billion years. Taking into account the time it took earth to solidify from its molten state in the beginning the age of the earth can be determined.

The age of the sun is determined differently. The sun emits electromagnetic radiation (including the light that we see). The spectrum of electromagnetic radiation emitted can be used to estimate the relative amount of hydrogen atoms that have already undergone fusion to produce helium atoms. Also astronomers are able to look at stars in distant systems. We generally know how far those stars are away from the earth and these stars that we see billions of light years away can help us to estimate how long ago the sun formed.

Answer 4

Reaction rates still remains the greatest mysteries in Physics and chemistry.
Taking rough data based on assumption of a Eigenvalue equation is basically a mathematical manipulation of what science thinks of reality. We actually have very little understanding how matter was formed and why atoms have the properties they display.

Though humans have made great progess in discovering atomic structures.

Radioactive decay is based on a simple decaying exponential function. the time constant in that equation is not a deterministic one but is a probabibalistic one. Hence certainty is as good as the estimate of the time constant.
On the other hand who is to say that formation of mass was based on an exponential function ;Humans did not create this world. So the apparent decay of isotopes is just based on uncertainties.

If we use the formula E=mc^2 we obtain the energy of the formed mass content. and if matter formed according to this formula. at the velocity of light the formation time of the earth would be the radius of the earth divided by the speed of light.
The formation time would be 2 tenths of a seconds. and that is quite a difference compared to 5 millions years.
So it is concluded the the 4.5 millions years estimate by the radioative decay formula has quite a gap compared to the E=mc^2 formula.
The record of Creation by the Creator of the Universe indicates 6 days.and that appears to be a long time considering that the Universe could have been constructed in even a shorter time let alone the earth's construction time.

Answer 5

1. Radiometric dating of rocks.
2. The earth is approximately the age of the sun. The sun's age can be estimated by it's type...how fast it is "burning" and the ratio of hydrogen to helium; it's mass; how much fuel is remaining etc. The answer is rather complex, but all of the factors add up to about 4.5BY.

Answer 6

By studying radioactive decay. By knowing what the half-lives are of certain radioactive isotopes they can calculate the age of objects.

This is the basis of carbon dating (when unstable carbon is used as a base reference- I think they use carbon-13.)

Answer 7

Its a guestimate. Just a point of reference really!
No one truly knows as the universe don't always obey the laws of physics!! Do it!
Even Stephen Hawkins recognises this!

Answer 8

How many candles or fingers? The problem might be that the Earth could have been struck many times and restarted. Two solar systems may have collided. I really don't have a clue either.

Answer 9

They don't know. They are just making a guess based in the little observations and comparisons of known physical phenomenum.

Answer 10

Its complete guesswork. You can never say for certain or even as a guess.4.5B years is in my books complete speculation. We cannot be sure of anything that is up to one thousand years old. Take my word for it.