Methods That Can Be Used For Determining The Age Of A Rock.

1. Introduction


2. Earth History


3.0 Methods of determining the age of the Rock.


3.1 How to Determine the Age of a Rock using Relative Dating.


3.2 principle of superposition:


3.3 Relative dating based on Location


4.0 Determine the age of a Rock using Absolute dating(Radio Radiometric dating).


5. Conclusion



1. Introduction

Rocks are without doubt very interesting things. They can tell us stories about the past. The future maybe? Much like trees, fossilized rocks provide wonderful insight into how we lived in the past. Several clever scientists were able to determine the age of some rocks by measuring radiometric elements in a rock. A geologist can determine the relative age of a rock by studying its degree of erosion, its type of sediment, and the fossils within it. The age of a rock can help you determine the geologic and climatic history that has shaped it.



2. Earth History

The story of rocks begins with the evolution of life on Earth, which eventually led to complex organisms that could leave behind fossilized remains. Eventually, these fossils began to accumulate in layers as sediments were deposited, forming what we refer to as rock formations. During the later part of Earth's history when dinosaurs ruled the land rocks did not yet exist in the form of recognizable sedimentary layers. Rock formations were formed only when the atmosphere grew thick enough to prevent the erosion of these layers by wind and rain. That means that all rocks today are less than 100 million years old, and most are younger than 50 million years old. As a result, they have been shaped by events that took place during one of three periods:


Early Archean era 3,844-2,542 Mya (million years ago)


Early Proterozoic era 2,441-1,844 Mya (million years ago)


Late Proterozoic era 1,844-1,554 Mya (million years ago)

Rocks are a fascinating mystery. On the one hand, they are ancient and varied in appearance, unlike anything we've seen before on Earth. On the other, they're all made of the same materials, just arranged in different ways but rocks and minerals give us a window into Earth's history. They can be used to test hypotheses about how Earth has changed over time and what might happen to it in the future. They also contain chemical evidence of the history of life on Earth they're not just something that happened but rather something that lives on and remains unchanged by time.


3.0 Methods of determining the age of the Rock.


There are two main ways to measure rock ages: radiometric dating and stratigraphy. Radiometric dating relies on the decay of radioactive elements from rocks and minerals some of which decay naturally but others can be artificially imposed with a low-energy beam of electromagnetic radiation (gamma rays or x-rays). Rocks older than about 100 million years have had all their radioactive material decayed; those younger than that still have some radioactive elements that haven't decayed yet. 


3.1 How to Determine the Age of a Rock using Relative Dating


Relative age is simple to determine. If one rock is on top of another, then the one on top is younger. That's a pretty easy concept to understand: It's the same as saying that if you were standing at the bottom of a staircase and saw a friend coming down the stairs, then you'd know that your friend was younger than you because she was "above" you.


 3.2 principle of superposition:


 Relative dating is based on the principle of superposition: When two layers of rock are deposited at the same time, they are likely to be found in the same relative position, even if each layer was deposited at a different point in time. To understand this, think about a sheet of paper lying on top of another sheet that's resting on top of a table. If you look at one side of the paper, you'll see that it's covered by writing; if you look at any other side, you'll see that it's covered by writing as well. In both cases, the writing will be on top of what came before it. In other words, the writing cannot be older than anything that appears underneath it must have been deposited at the time those other things were deposited.



3.3 Relative dating based on Location


You'll always find out more about the age of rocks by looking at them in person. By examining the composition of the rock and its surroundings, you can get a pretty good idea of how old it is. But if you're not comfortable with physical inspection, there are some other ways to establish the age of a rock.


Is it from one country only? If so, the specific region is an excellent place to start. Rocks from similar regions usually have similar ages because they were formed at about the same time.  If a rock comes from one area but has features that seem to indicate that it's older than many others in that region, it's probably older overall. 


Is it from a single location? If so, try to determine whether it was formed in situ that is, in its current location or near where it now sits, or if it was transported there by wind or water. Geologists have discovered rocks around the world with dates as young as 1 million years old! Those aren't just local oddities; they're evidence of an ancient global climate change. 


4.0 Determine the age of a Rock using Absolute dating(Radio Radiometric dating).


Absolute age dating is a bit more complicated. Relative age dates stratigraphy, laws of superposition, etc. can only tell you whether one rock is older than or younger than another; absolute age dating can tell you exactly how old each one is. Geologists use radioactive dating to determine the absolute age of rocks and minerals. Radioactive dating can be used for igneous, metamorphic, or sedimentary rocks. Radiometric dating is usually done using uranium-lead dating, potassium-argon dating, or rubidium-strontium dating. The isotope of an element that decays is called a parent isotope; the isotope that it decays into is called a daughter isotope. The half-life of a radioactive element is the amount of time it takes for half of the parent isotopes to decay into daughter isotopes. The half-life of uranium-238 is 4.5 billion years, while the half-life of its daughter product, lead-206 is only 13 million years. A rock that contains both uranium and lead can be dated by measuring the proportion of each isotope in the rock. If there are equal amounts of uranium and lead in the rock, then it is 4.5 billion years old (because one-half life has passed). If the amount of lead has doubled since the rock was formed, then it has been through 2 half-lives (9 billion years).

In a nutshell, the method of radioactive dating is to examine the amount of radioactive decay in an isotope and then calculate when the material was formed. Carbon-14 dating is one example of an isotope that decays through radioactive decay. The half-life of carbon-14 is 5730 years.





5. Conclusion


If you can find out what type of rock the sample you are dating is made from, then you may be able to use a simple method of relative dating to estimate its age. However, if the rock cannot easily be broken down into smaller pieces, then relative dating will not be possible and you will need to resort to a radiometric dating method.

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