Geologic Time. From the beginning of this course, we have stated that the Earth is about 4. How do we know this and how do we know the ages of other events in Earth history? Prior to the late 17th century, geologic time was thought to be the same as historical time. The goal of this lecture is come to come to a scientific understanding of geologic time and the age of the Earth. In order to do so we will have to understand the following:. In order to understand how scientists deal with time we first need to understand the concepts of relative age and numeric age. By carefully digging, we have found that each trash pit shows a sequence of layers. Although the types of trash in each pit is quite variable, each layer has a distinctive kind of trash that distinguishes it from other layers in the pits.
Geological Time Scale
Despite how like a relatively stable place, the Earth’s surface has changed dramatically over are past 4. Mountains have been built and eroded, continents and oceans have moved dating distances, and the Earth has fossils from being extremely cold and almost completely covered with ice to being very warm and ice-free.
These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this dating, the Earth’s surface is moving and changing. As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.
Earth Science 11/Geology 12 iii. Credits. Credits Relative Age Dating with Fossils. Kellas Give an explanation for the patterns noted in questions 1 and 2.
There are two types of age determinations. Geologists in the late 18th and early 19th century studied rock layers and the fossils in them to determine relative age. William Smith was one of the most important scientists from this time who helped to develop knowledge of the succession of different fossils by studying their distribution through the sequence of sedimentary rocks in southern England. It wasn’t until well into the 20th century that enough information had accumulated about the rate of radioactive decay that the age of rocks and fossils in number of years could be determined through radiometric age dating.
This activity on determining age of rocks and fossils is intended for 8th or 9th grade students. It is estimated to require four hours of class time, including approximately one hour total of occasional instruction and explanation from the teacher and two hours of group team and individual activities by the students, plus one hour of discussion among students within the working groups.
Explore this link for additional information on the topics covered in this lesson: Geologic Time. Students not only want to know how old a fossil is, but they want to know how that age was determined.
Geologists analyze geologic time in two different ways: in terms of relative geologic age , and in terms of absolute or numeric geologic age. Relative geologic age refers to the order in which geologic events occurred. Relative geologic age is established, based on the order in which layers of sediment are stacked, with the younger layer originally on top. By using the principles of relative geologic age, the sequence of geologic events — what happened first, what happened next, what happened last — can be established.
In order to determine the relative ages we use the four fundamental principles of relative age dating that were explained to you on the concepts page. Geologists.
Honolulu Community College Earth Revealed. Oh, hi! I was just reading here, and I found an interesting quote that I’d like to share with you. Back in , a geologist named Adolph Knopp wrote a passage about geologic time. Knopp wrote “If I were asked as a geologist, what’s the single greatest contribution of the Science of Geology to modern civilized thought,the answer would be the realization of the immense length of time. So vast is the span of time recorded in the history of the Earth that it’s generally distinguished from the more modest kinds of time by being called “geologic time.
Estimates of the age of the Earth have been expanding throughout time. The key to understanding this immensity of geologic time is really the Principal of Uniformitarianism. You see, there’s really no need for supernatural intervention if time can explain the existing geologic features on Earth. Some people would even argue that understanding the long stretch to geologic time requires a much less of a stretch of imagination than trying to understand supernatural intervention.
High School Earth Science/Geologic Time Scale
A few days ago, I wrote a post about the basins of the Moon — a result of a trip down a rabbit hole of book research. In the science of geology, there are two main ways we use to describe how old a thing is or how long ago an event took place. There are absolute ages and there are relative ages. People love absolute ages.
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. Historians love to quote the dates of famous events in human history. They recount days of national loss and tragedy like December 7, and September 11, And they remember birthdays: July 4, and, of course, February 12, 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. But how can we be sure of those age estimates? Earth scientists have developed numerous independent yet consistent lines of evidence that point to an incredibly old Earth. But first, a warning: it is difficult for anyone to conceive of such an immense time span as 4. The oldest humans the current record according to Guinness is held by a French woman who lived to celebrate her nd birthday fall far short of living for 4.
All of recorded human history is much less than 4.
The end product of correlation is a mental abstraction called the geologic column. In order to communicate the fine structure of this so-called column, it has been subdivided into smaller units. Lines are drawn on the basis of either significant changes in fossil forms or discontinuities in the rock record i.
In the upper part of the geologic column, where fossils abound, these rock systems and geologic periods are the basic units of rock and time. Lumping of periods results in eras, and splitting gives rise to epochs.
let scientists use absolute dating to give ages to each chunk of time on the geologic time scale.
Here I want to concentrate on another source of error, namely, processes that take place within magma chambers. To me it has been a real eye opener to see all the processes that are taking place and their potential influence on radiometric dating. Radiometric dating is largely done on rock that has formed from solidified lava. Lava properly called magma before it erupts fills large underground chambers called magma chambers. Most people are not aware of the many processes that take place in lava before it erupts and as it solidifies, processes that can have a tremendous influence on daughter to parent ratios.
Such processes can cause the daughter product to be enriched relative to the parent, which would make the rock look older, or cause the parent to be enriched relative to the daughter, which would make the rock look younger.
How Old is Earth, and How Do We Know?
Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence. The method of reading the order is called stratigraphy layers of rock are called strata. Relative dating does not provide actual numerical dates for the rocks. Next time you find a cliff or road cutting with lots of rock strata, try working out the age order using some simple principles:. Fossils are important for working out the relative ages of sedimentary rocks. Throughout the history of life, different organisms have appeared, flourished and become extinct.
By Beth Geiger. June 13, at am. Imagine the nearly unimaginable: 4. To grasp just how old Earth is, imagine fitting its entire history into one calendar year. Fish first swam onto the scene in late November. Dinosaurs stomped around from December 16 until December The first modern humans — Homo sapiens — were real late-comers.