How we estimate the age of Earth by carbon Dating?

 

What is Carbon Dating?

 

The determination of the age or date of organic matter from the relative proportions of the carbon isotopes carbon-12 and carbon-14 that it contains . The ratio between them changes as radioactive carbon-14 decays and is not replaced by exchange with the atmosphere.

How does it work?

Radiocarbon dating works by comparing the three different isotopes of carbon. Isotopes of a particular element have the same number of protons in their nucleus, but different numbers of neutrons. This means that although they are very similar chemically, they have different masses

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How Old is Earth?

Earth scientists have devised many complementary and consistent techniques to estimate the ages of geologic events. Annually deposited layers of sediments or ice document hundreds of thousands of years of continuous Earth history .

Gradual rates of mountain building, erosion of mountains, and the motions of tectonic plates imply hundreds of millions of years of change. Radiometric dating, which relies on the predictable decay of radioactive isotopes of carbon, uranium, potassium, and other elements, provides accurate age estimates for events back to the formation of Earth more than 4.5 billion years ago.

These and other dating techniques are mutually consistent and underscore the reality of “deep time” in Earth history.

Historians love to quote the dates of famous events in human history. They celebrate great accomplishments and discoveries, such as the Wright Brothers’ first flight of December 17, 1903, and the first manned moon landing on July 20, 1969.

 

They recount days of national loss and tragedy like December 7, 1941 and September 11, 2001. And they remember birthdays: July 4, 1776 and, of course, February 12, 1809 (the coincident birthdays of Charles Darwin and Abraham Lincoln). We trust the validity of these historic moments because of the unbroken written and oral record that links us to the not-so-distant past.

Total Age Of Earth?

 

Geologists also love to quote historic age estimates: about 12,500 years ago, when the last great glaciation ended and humans began to settle North America; 65 million years ago, when the dinosaurs and many other creatures became extinct; the Cambrian boundary at 542 million years ago, when diverse animals with hard shells suddenly appeared; 4.56 billion years ago, when the Sun and Earth formed from a vast cloud of dust and gas.

But how can we be sure of those age estimates?

There’s no written record past a few thousand years, nor is there any oral tradition that can inform estimates of Earth’s ancient chronology.

 

How we calculate it by Carbon Dating?

 

Earth scientists have devised many complementary

Consistent techniques to estimate the ages of geologic

Events . Annually deposited layers of sediments or ice

document hundreds of thousands of years of continuous Earth

history. Gradual rates of mountain building, erosion of

mountains, and the motions of tectonic plates imply hundreds

of millions of years of change.

 

 

Radiometric dating, which relies on the predictable decay of radioactive isotopes of carbon, uranium, potassium, and other elements, provides

accurate age estimates for events back to the formation of

Earth more than 4.5 billion years ago . These and other dating

techniques are mutually consistent and underscore the reality

of “deep time” in Earth history.

 

Annual Rock Clocks

Annual Rock Clocks

Rocks reveal their ages of formation in several ways and

 provide Earth scientists with their most reliable clocks.

The most straightforward geologic timekeepers are rock

formations with annual layers. Annual tree rings provide

a familiar analog .

 Each year of a tree’s Life is marked by a distinctive ring, as growth increases in spring and slows the following winter.

The oldest trees on Earth are a few thousand years old, but tree ring dating.Sedimentary rocks, too, can display annual layering.

“varves,” that result from seasonal differences in sediment deposition (Kemp 1996).

 

The most dramatic varve deposits, such as a meticulously documented 13,527-year sequence in glacial lakes in Sweden, occur as thin

alternating light and dark layers, representing coarser-

grained spring sediments and finer winter sediments,

respectively.

 

Ancient varved deposits sometimes preserve much longer time spans: the finely laminated Green River shale in Wyoming features continuous vertical sections with more than a million such layers .

The oldest annual layers are extracted from ice cores, whose

laminae arise from seasonal variations in snowfall .

 

 A 2,000-meter ice core from East Antarctica reveals 160,000

annual layers of accumulation, year-by-year, snow layer by

snow layer. And those annual layers rest atop another

2,000 meters of ice, which sit on vastly older rocks.

 

 

Similar ages of ice cores comprise Greenland’s thick glacial deposits.

The obvious conclusion is that at least a million years is

needed to account for many surficial deposits of sediment

and ice. Earth must be much older than that, but how old?

Geologic Rates

 

Slow, inexorable changes of Earth’s dynamic surface provide

a vivid, if approximate, measure of deep time. Consider three

simple “back-of-the-envelope” calculations. First, how old is

the big island of Hawaii? The massive Hawaiian Islands rose

from the Pacific as volcanoes periodically added layers of lava

(Fig. 5). From modern-day eruptions, we know that active

volcanoes grow by perhaps a meter every century. 

The highest point on the big island of Hawaii is Mauna Kea at

4,205 meters above sea level. However, the volcano rises.

 Radiometric Dating.

 

The physical process of radioactive decay has provided

Earth scientists, anthropologists, and evolutionary biolo-

gists with their most important method for determining the

absolute age of rocks and other materials (Dalrymple 1991;

Dickin 2005).

This remarkable technique, which depends on measurements of the distinctive properties of radioactive .

The b est-known radiometric dating method involves the

isotope carbon-14, with a half life of 5,730 years.

Every living organism takes in carbon during its lifetime.

At this moment, your body is taking the carbon in your food and

converting it to tissue, and the same is true of all other

animals. Plants are taking in carbon dioxide from the air

and turning it into roots, stems, and leaves.

 

 

 

 Most of this carbon (about 99%) is in the form of stable (non-

radioactive) carbon-12, while perhaps 1% is the slightly

heavier stable carbon-13.

 

But a certain small percentage of the carbon in your body and every other living thing—no more than one carbon atom in every trillion—is in the form of radioactive carbon-14.

Estimation

 

Planets like the Earth cannot form unless elements heavier than helium are available. These heavy elements, or `metals', were not produced in the big bang. They result from fusion inside stars and have been gradually building up over the lifetime of the Universe. Recent observations indicate that the presence of giant extrasolar planets at small distances from their host stars, is strongly correlated with high metallicity of the host stars.

 

 The presence of these close-orbiting giants is incompatible with the existence of earth-like planets. Thus, there may be a Goldilocks selection effect: with too little metallicity, earths are unable to form for lack of material, with too much metallicity giant planets destroy earths. Here I quantify these effects and obtain the probability, as a function of metallicity, for a stellar system to harbour an earth-like planet. I combine this probability with current estimates of the star formation rate and of the gradual build up of metals in the Universe to obtain an estimate of the age distribution of earth-like planets in the Universe.

 

 

 The analysis done here indicates that three quarters of the earth-like planets in the Universe are older than the Earth and that their average age is 1.8 +/- 0.9 billion years older than the Earth. If life forms readily on earth-like planets - as suggested by the rapid appearance of life on Earth - this analysis gives us an age distribution for life on such planets and a rare clue about how we compare to other life which may inhabit the Universe.