{"id":2245,"date":"2016-07-05T18:03:54","date_gmt":"2016-07-05T18:03:54","guid":{"rendered":"https:\/\/opentextbc.ca\/geology\/?post_type=chapter&p=2245"},"modified":"2019-07-30T18:26:42","modified_gmt":"2019-07-30T18:26:42","slug":"8-6-understanding-geological-time","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/geology\/chapter\/8-6-understanding-geological-time\/","title":{"raw":"8.6 Understanding Geological Time","rendered":"8.6 Understanding Geological Time"},"content":{"raw":"It\u2019s one thing to know the facts about geological time \u2014 how long it is, how we measure it, how we divide it up, and what we call the various periods and epochs \u2014 but it is quite another to really understand geological time. The problem is that our lives are short and our memories are even shorter. Our experiences span only a few decades, so we really don\u2019t have a way of knowing what 11,700 years means. What\u2019s more, it\u2019s hard for us to understand how 11,700 years differs from 65.5 Ma, or even from 1.8 Ga. It\u2019s not that we can\u2019t comprehend what the numbers mean \u2014 we can all get that figured out with a bit of practice \u2014 but even if we do know the numerical meaning of 65.5 Ma, we can\u2019t really appreciate how long ago it was.\r\n\r\nYou may be wondering why it\u2019s so important to really \u201cunderstand\u201d geological time. There are some very good reasons. One is so that we can fully understand how geological processes that seem impossibly slow can produce anything of consequence. For example, we are familiar with the concept of driving from one major city to another: a journey of several hours at around 100 km\/h. Continents move toward each other at rates of a fraction of a millimetre per day, or something in the order of 0.00000001 km\/h, and yet, at this impossibly slow rate (try walking at that speed!), they can move thousands of kilometres. Sediments typically accumulate at even slower rates \u2014 less than a millimetre per year \u2014 but still they are thick enough to be thrust up into monumental mountains and carved into breathtaking canyons.\r\n\r\nAnother reason is that for our survival on this planet, we need to understand issues like extinction of endangered species and anthropogenic<\/strong> (human-caused) climate change. Some people, who don\u2019t understand geological time, are quick to say that the climate has changed in the past, and that what is happening now is no different. And it certainly has changed in the past. For example, from the Eocene (50 Ma) to the present day, Earth\u2019s climate cooled by about 12\u00b0C. That\u2019s a huge change that ranks up there with many of the important climate changes of the distant past, and yet the rate of change over that time was only 0.000024\u00b0C\/century. Anthropogenic climate change has been 1.1\u00b0C over the past 100 years,[footnote]Climate change data from NASA Goddard Institute for Space Studies: http:\/\/data.giss.nasa.gov\/gistemp\/tabledata_v3\/GLB.Ts.txt[\/footnote] and that is 45,800 times faster than the rate of natural climate change since the Eocene!\r\n\r\nOne way to wrap your mind around geological time is to put it into the perspective of single year, because we all know how long it is from one birthday to the next. At that rate, each hour of the year is equivalent to approximately 500,000 years, and each day is equivalent to 12.5 million years.\r\n\r\nIf all of geological time is compressed down to a single year, Earth formed on January 1, and the first life forms evolved in late March (~3,500 Ma). The first large life forms appeared on November 13 (~600 Ma), plants appeared on land around November 24, and amphibians on December 3. Reptiles evolved from amphibians during the first week of December and dinosaurs and early mammals evolved from reptiles by December 13, but the dinosaurs, which survived for 160 million years, were gone by Boxing Day (December 26). The Pleistocene Glaciation got started at around 6:30 p.m. on New Year\u2019s Eve, and the last glacial ice left southern Canada by 11:59 p.m.\r\n\r\nIt\u2019s worth repeating: on this time scale, the earliest ancestors of the animals and plants with which we are familiar did not appear on Earth until mid-November, the dinosaurs disappeared after Christmas, and most of Canada was periodically locked in ice from 6:30 to 11:59 p.m. on New Year\u2019s Eve. As for people, the first to inhabit B.C. got here about one minute before midnight, and the first Europeans arrived about two seconds before midnight.\r\n\r\nIt is common for the popular press to refer to distant past events as being \u201cprehistoric.\u201d For example, dinosaurs are reported as being \u201cprehistoric creatures,\u201d even by the esteemed National Geographic Society.[footnote]http:\/\/science.nationalgeographic.com\/science\/prehistoric-world\/[\/footnote]\u00a0The written records of our history date back to about 6,000 years ago, so anything prior to that is considered \u201cprehistoric.\u201d But to call the dinosaurs prehistoric is equivalent to \u2014 and about as useful as \u2014 saying that Singapore is beyond the city limits of Kamloops! If we are going to become literate about geological time, we have to do better than calling dinosaurs, or early horses (54 Ma), or even early humans (2.8 Ma), \u201cprehistoric.\u201d\r\n
\r\n

Exercises<\/p>\r\n\r\n<\/header>\r\n

\r\n\r\nExercise 8.5 <\/strong>What Happened on Your Birthday?<\/strong>\r\n\r\nUsing the \u201call of geological time compressed to one year\u201d concept, determine the geological date that is equivalent to your birthday. First go here: http:\/\/mistupid.com\/calendar\/dayofyear.htm<\/a> to find out which day of the year your birth date is. Then divide that number by 365, and multiply that number by 4,570 to determine the time (in millions since the beginning<\/em> of geological time). Finally subtract that number from 4,570 to determine the date back from the present.\r\n\r\nFor example, April Fool\u2019s Day (April 1) is day 91 of the year: 91\/365 = 0.2493. 0.2493 x 4,570 = 1,139 million years from the start of time, and 4,570 - 1,193 = 3,377 Ma is the geological date.\r\n\r\nFinally, go to the Foundation for Global Community\u2019s \u201cWalk through Time\u201d website at http:\/\/www.globalcommunity.org\/wtt\/walk_menu\/<\/a> to find out what was happening on your day. The nearest date to 3,377 Ma is 3,400 Ma. Bacteria ruled the world at 3,400 Ma, and there\u2019s a discussion about their lifestyles.\r\n\r\n<\/div>","rendered":"

It\u2019s one thing to know the facts about geological time \u2014 how long it is, how we measure it, how we divide it up, and what we call the various periods and epochs \u2014 but it is quite another to really understand geological time. The problem is that our lives are short and our memories are even shorter. Our experiences span only a few decades, so we really don\u2019t have a way of knowing what 11,700 years means. What\u2019s more, it\u2019s hard for us to understand how 11,700 years differs from 65.5 Ma, or even from 1.8 Ga. It\u2019s not that we can\u2019t comprehend what the numbers mean \u2014 we can all get that figured out with a bit of practice \u2014 but even if we do know the numerical meaning of 65.5 Ma, we can\u2019t really appreciate how long ago it was.<\/p>\n

You may be wondering why it\u2019s so important to really \u201cunderstand\u201d geological time. There are some very good reasons. One is so that we can fully understand how geological processes that seem impossibly slow can produce anything of consequence. For example, we are familiar with the concept of driving from one major city to another: a journey of several hours at around 100 km\/h. Continents move toward each other at rates of a fraction of a millimetre per day, or something in the order of 0.00000001 km\/h, and yet, at this impossibly slow rate (try walking at that speed!), they can move thousands of kilometres. Sediments typically accumulate at even slower rates \u2014 less than a millimetre per year \u2014 but still they are thick enough to be thrust up into monumental mountains and carved into breathtaking canyons.<\/p>\n

Another reason is that for our survival on this planet, we need to understand issues like extinction of endangered species and anthropogenic<\/strong> (human-caused) climate change. Some people, who don\u2019t understand geological time, are quick to say that the climate has changed in the past, and that what is happening now is no different. And it certainly has changed in the past. For example, from the Eocene (50 Ma) to the present day, Earth\u2019s climate cooled by about 12\u00b0C. That\u2019s a huge change that ranks up there with many of the important climate changes of the distant past, and yet the rate of change over that time was only 0.000024\u00b0C\/century. Anthropogenic climate change has been 1.1\u00b0C over the past 100 years,[1]<\/sup><\/a> and that is 45,800 times faster than the rate of natural climate change since the Eocene!<\/p>\n

One way to wrap your mind around geological time is to put it into the perspective of single year, because we all know how long it is from one birthday to the next. At that rate, each hour of the year is equivalent to approximately 500,000 years, and each day is equivalent to 12.5 million years.<\/p>\n

If all of geological time is compressed down to a single year, Earth formed on January 1, and the first life forms evolved in late March (~3,500 Ma). The first large life forms appeared on November 13 (~600 Ma), plants appeared on land around November 24, and amphibians on December 3. Reptiles evolved from amphibians during the first week of December and dinosaurs and early mammals evolved from reptiles by December 13, but the dinosaurs, which survived for 160 million years, were gone by Boxing Day (December 26). The Pleistocene Glaciation got started at around 6:30 p.m. on New Year\u2019s Eve, and the last glacial ice left southern Canada by 11:59 p.m.<\/p>\n

It\u2019s worth repeating: on this time scale, the earliest ancestors of the animals and plants with which we are familiar did not appear on Earth until mid-November, the dinosaurs disappeared after Christmas, and most of Canada was periodically locked in ice from 6:30 to 11:59 p.m. on New Year\u2019s Eve. As for people, the first to inhabit B.C. got here about one minute before midnight, and the first Europeans arrived about two seconds before midnight.<\/p>\n

It is common for the popular press to refer to distant past events as being \u201cprehistoric.\u201d For example, dinosaurs are reported as being \u201cprehistoric creatures,\u201d even by the esteemed National Geographic Society.[2]<\/sup><\/a>\u00a0The written records of our history date back to about 6,000 years ago, so anything prior to that is considered \u201cprehistoric.\u201d But to call the dinosaurs prehistoric is equivalent to \u2014 and about as useful as \u2014 saying that Singapore is beyond the city limits of Kamloops! If we are going to become literate about geological time, we have to do better than calling dinosaurs, or early horses (54 Ma), or even early humans (2.8 Ma), \u201cprehistoric.\u201d<\/p>\n

\n
\n

Exercises<\/p>\n<\/header>\n

\n

Exercise 8.5 <\/strong>What Happened on Your Birthday?<\/strong><\/p>\n

Using the \u201call of geological time compressed to one year\u201d concept, determine the geological date that is equivalent to your birthday. First go here: http:\/\/mistupid.com\/calendar\/dayofyear.htm<\/a> to find out which day of the year your birth date is. Then divide that number by 365, and multiply that number by 4,570 to determine the time (in millions since the beginning<\/em> of geological time). Finally subtract that number from 4,570 to determine the date back from the present.<\/p>\n

For example, April Fool\u2019s Day (April 1) is day 91 of the year: 91\/365 = 0.2493. 0.2493 x 4,570 = 1,139 million years from the start of time, and 4,570 – 1,193 = 3,377 Ma is the geological date.<\/p>\n

Finally, go to the Foundation for Global Community\u2019s \u201cWalk through Time\u201d website at http:\/\/www.globalcommunity.org\/wtt\/walk_menu\/<\/a> to find out what was happening on your day. The nearest date to 3,377 Ma is 3,400 Ma. Bacteria ruled the world at 3,400 Ma, and there\u2019s a discussion about their lifestyles.<\/p>\n<\/div>\n<\/div>\n

  1. Climate change data from NASA Goddard Institute for Space Studies: http:\/\/data.giss.nasa.gov\/gistemp\/tabledata_v3\/GLB.Ts.txt ↵<\/a><\/li>
  2. http:\/\/science.nationalgeographic.com\/science\/prehistoric-world\/ ↵<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":2,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2245","chapter","type-chapter","status-publish","hentry"],"part":3169,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters\/2245","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":2,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters\/2245\/revisions"}],"predecessor-version":[{"id":3049,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters\/2245\/revisions\/3049"}],"part":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/parts\/3169"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters\/2245\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/media?parent=2245"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapter-type?post=2245"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/contributor?post=2245"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/license?post=2245"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}