{"id":1981,"date":"2016-07-05T17:18:42","date_gmt":"2016-07-05T17:18:42","guid":{"rendered":"https:\/\/opentextbc.ca\/geology\/?post_type=chapter&p=1981"},"modified":"2019-07-30T18:09:55","modified_gmt":"2019-07-30T18:09:55","slug":"1-6-geological-time","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/geology\/chapter\/1-6-geological-time\/","title":{"raw":"1.6 Geological Time","rendered":"1.6 Geological Time"},"content":{"raw":"In 1788, after many years of geological study, James Hutton, one of the great pioneers of geology, wrote the following about the age of Earth: The result, therefore, of our present enquiry is, that we find no vestige of a beginning \u2014 no prospect of an end<\/em>.[footnote]Hutton, J, 1788.\u00a0Theory of the Earth; or an investigation of the laws observable in the composition, dissolution, and restoration of land upon the Globe. Transactions of the Royal Society of Edinburgh.[\/footnote]\u00a0Of course he wasn\u2019t exactly correct, there was a beginning and there will be an end to Earth, but what he was trying to express is that geological time is so vast that we humans, who typically live for less than a century, have no means of appreciating how much geological time there is. Hutton didn\u2019t even try to assign an age to Earth, but we now know that it is approximately 4,570 million years old. Using the scientific notation for geological time, that is 4,570 Ma<\/strong> (for mega annum<\/em> or \u201cmillions of years\u201d) or 4.57 Ga<\/strong> (for giga<\/em> annum<\/em> or billions of years). More recent dates can be expressed in ka<\/strong> (kilo<\/em> annum<\/em>); for example, the last cycle of glaciation ended at approximately 11.7 ka or 11,700 years ago. This notation will be used for geological dates throughout this book.\r\n
\r\n

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

Exercise 1.3 Using Geological Time Notation <\/strong>To help you understand the scientific notation for geological time, write the following out in numbers (for example, 3.23 Ma = 3,230,000 years).\r\n\r\n\r\n\r\n\r\n\r\n
2.75 ka<\/strong><\/td>\r\n<\/tr>\r\n
0.93 Ga<\/strong><\/td>\r\n<\/tr>\r\n
14.2 Ma<\/strong><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nWe use this notation to describe times from the present, but not to express time differences in the past. For example, we could say that the dinosaurs lived from about 225 Ma to 65 Ma, which is 160 million years, but we would not say that they lived for 160 Ma.\r\n\r\n<\/div>\r\n<\/div>\r\nUnfortunately, knowing how to express geological time doesn\u2019t really help us understand or appreciate its extent. A version of the geological time scale is included as Figure 1.9. Unlike time scales you\u2019ll see in other places, or even later in this book, this time scale is linear throughout its length, meaning that 50 Ma during the Cenozoic<\/strong> is the same thickness as 50 Ma during the Hadean<\/strong>\u2014in each case about the height of the \u201cM\u201d in Ma. The Pleistocene glacial epoch began at about 2.6 Ma, which is equivalent to half the thickness of the thin grey line at the top of the yellow bar marked \u201cCenozoic.\u201d Most other time scales have earlier parts of Earth\u2019s history compressed so that more detail can be shown for the more recent parts. That makes it difficult to appreciate the extent of geological time.\r\n\r\n[caption id=\"attachment_1153\" align=\"aligncenter\" width=\"166\"]\"The<\/a> Figure 1.9 The geological time scale [SE][\/caption]To create some context, the Phanerozoic<\/strong> Eon (the last 542 million years) is named for the time during which visible (phaneros<\/em>) life (zoi<\/em>) is present in the geological record. In fact, large organisms \u2014 those that leave fossils visible to the naked eye \u2014 have existed for a little longer than that, first appearing around 600 Ma, or a span of just over 13% of geological time. Animals have been on land for 360 million years, or 8% of geological time. Mammals have dominated since the demise of the dinosaurs around 65 Ma, or 1.5% of geological time, and the genus Homo<\/em> has existed since approximately 2.2 Ma, or 0.05% (1\/2,000th) of geological time.\r\n\r\nGeologists (and geology students) need to understand geological time. That doesn\u2019t mean simply memorizing the geological time scale; instead, it means getting your mind around the concept that although most geological processes are extremely slow, very large and important things can happen if such processes continue for enough time.\r\n\r\nFor example, the Atlantic Ocean between Nova Scotia and northwestern Africa has been getting wider at a rate of about 2.5 cm per year. Imagine yourself taking a journey at that rate \u2014 it would be impossibly and ridiculously slow. And yet, since it started to form around 200 Ma (just 4% of geological time), the Atlantic Ocean has grown to a width of over 5,000 km!\r\n\r\nA useful mechanism for understanding geological time is to scale it all down into one year. The origin of the solar system and Earth at 4.57 Ga would be represented by January 1, and the present year would be represented by the last tiny fraction of a second on New Year\u2019s Eve. At this scale, each day of the year represents 12.5 million years; each hour represents about 500,000 years; each minute represents 8,694 years; and each second represents 145 years. Some significant events in Earth\u2019s history, as expressed on this time scale, are summarized on Table 1.1.\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Table 1.1\u00a0 A summary of some important geological dates expressed as if all of geological time was condensed into one year [SE]<\/caption>\r\n
Event<\/strong><\/th>\r\nApproximate Date<\/strong><\/th>\r\nCalendar Equivalent<\/strong><\/th>\r\n<\/tr>\r\n
Formation of oceans and continents<\/td>\r\n4.5 - 4.4 Ga<\/td>\r\nJanuary<\/td>\r\n<\/tr>\r\n
Evolution of the first primitive life forms<\/td>\r\n3.8 Ga<\/td>\r\nearly March<\/td>\r\n<\/tr>\r\n
Formation of British Columbia\u2019s oldest rocks<\/td>\r\n2.0 Ga<\/td>\r\nJuly<\/td>\r\n<\/tr>\r\n
Evolution of the first multi-celled animals<\/td>\r\n0.6 Ga or 600 Ma<\/td>\r\nNovember 15<\/td>\r\n<\/tr>\r\n
Animals first crawled onto land<\/td>\r\n360 Ma<\/td>\r\nDecember 1<\/td>\r\n<\/tr>\r\n
Vancouver Island reached North America and the Rocky Mountains were formed<\/td>\r\n90 Ma<\/td>\r\nDecember 25<\/td>\r\n<\/tr>\r\n
Extinction of the non-avian dinosaurs<\/td>\r\n65 Ma<\/td>\r\nDecember 26<\/td>\r\n<\/tr>\r\n
Beginning of the Pleistocene ice age<\/td>\r\n2 Ma or 2000 ka<\/td>\r\n8 p.m., December, 31<\/td>\r\n<\/tr>\r\n
Retreat of the most recent glacial ice from southern Canada<\/td>\r\n14 ka<\/td>\r\n11:58 p.m., December 31<\/td>\r\n<\/tr>\r\n
Arrival of the first people in British Columbia<\/td>\r\n10 ka<\/td>\r\n11:59 p.m., December 31<\/td>\r\n<\/tr>\r\n
Arrival of the first Europeans on the west coast of what is now Canada<\/td>\r\n250 years ago<\/td>\r\n2 seconds before midnight, December 31<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n \r\n\r\n\u00a0<\/strong>\r\n
\r\n

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

\r\n\r\nExercise 1.4 Take a Trip through Geological Time<\/strong>\r\n\r\nWe\u2019re going on a road trip! Pack some snacks and grab some of your favourite music. We\u2019ll start in Tofino on Vancouver Island and head for the Royal Tyrrell Museum just outside of Drumheller, Alberta, 1,500 km away. Along the way, we\u2019ll talk about some important geological sites that we pass by, and we\u2019ll use the distance as a way of visualizing the extent of geological time. Of course it\u2019s just a \u201cvirtual\u201d road trip, but it will be fun anyway. To join in, go to: https:\/\/barabus.tru.ca\/geol2051\/road_trip\/road_trip.html<\/a>\r\n\r\nOnce you\u2019ve had a chance to do the road trip, answer these questions:\r\n\r\n1. We need oxygen to survive, and yet the first presence of free oxygen (O2<\/sub> gas) in the atmosphere and the oceans was a \u201ccatastrophe\u201d for some organisms. When did this happen and why was it a catastrophe?\r\n\r\n2. Approximately how much time elapsed between the colonization of land by plants and animals?\r\n\r\n3. Explain why the evolution of land plants was such a critical step in the evolution of life on Earth.\r\n\r\n<\/div>","rendered":"

In 1788, after many years of geological study, James Hutton, one of the great pioneers of geology, wrote the following about the age of Earth: The result, therefore, of our present enquiry is, that we find no vestige of a beginning \u2014 no prospect of an end<\/em>.[1]<\/sup><\/a>\u00a0Of course he wasn\u2019t exactly correct, there was a beginning and there will be an end to Earth, but what he was trying to express is that geological time is so vast that we humans, who typically live for less than a century, have no means of appreciating how much geological time there is. Hutton didn\u2019t even try to assign an age to Earth, but we now know that it is approximately 4,570 million years old. Using the scientific notation for geological time, that is 4,570 Ma<\/strong> (for mega annum<\/em> or \u201cmillions of years\u201d) or 4.57 Ga<\/strong> (for giga<\/em> annum<\/em> or billions of years). More recent dates can be expressed in ka<\/strong> (kilo<\/em> annum<\/em>); for example, the last cycle of glaciation ended at approximately 11.7 ka or 11,700 years ago. This notation will be used for geological dates throughout this book.<\/p>\n

\n
\n

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

Exercise 1.3 Using Geological Time Notation <\/strong>To help you understand the scientific notation for geological time, write the following out in numbers (for example, 3.23 Ma = 3,230,000 years).<\/p>\n\n\n\n\n\n
2.75 ka<\/strong><\/td>\n<\/tr>\n
0.93 Ga<\/strong><\/td>\n<\/tr>\n
14.2 Ma<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

We use this notation to describe times from the present, but not to express time differences in the past. For example, we could say that the dinosaurs lived from about 225 Ma to 65 Ma, which is 160 million years, but we would not say that they lived for 160 Ma.<\/p>\n<\/div>\n<\/div>\n

Unfortunately, knowing how to express geological time doesn\u2019t really help us understand or appreciate its extent. A version of the geological time scale is included as Figure 1.9. Unlike time scales you\u2019ll see in other places, or even later in this book, this time scale is linear throughout its length, meaning that 50 Ma during the Cenozoic<\/strong> is the same thickness as 50 Ma during the Hadean<\/strong>\u2014in each case about the height of the \u201cM\u201d in Ma. The Pleistocene glacial epoch began at about 2.6 Ma, which is equivalent to half the thickness of the thin grey line at the top of the yellow bar marked \u201cCenozoic.\u201d Most other time scales have earlier parts of Earth\u2019s history compressed so that more detail can be shown for the more recent parts. That makes it difficult to appreciate the extent of geological time.<\/p>\n

\"The<\/a>
Figure 1.9 The geological time scale [SE]<\/figcaption><\/figure>\n

To create some context, the Phanerozoic<\/strong> Eon (the last 542 million years) is named for the time during which visible (phaneros<\/em>) life (zoi<\/em>) is present in the geological record. In fact, large organisms \u2014 those that leave fossils visible to the naked eye \u2014 have existed for a little longer than that, first appearing around 600 Ma, or a span of just over 13% of geological time. Animals have been on land for 360 million years, or 8% of geological time. Mammals have dominated since the demise of the dinosaurs around 65 Ma, or 1.5% of geological time, and the genus Homo<\/em> has existed since approximately 2.2 Ma, or 0.05% (1\/2,000th) of geological time.<\/p>\n

Geologists (and geology students) need to understand geological time. That doesn\u2019t mean simply memorizing the geological time scale; instead, it means getting your mind around the concept that although most geological processes are extremely slow, very large and important things can happen if such processes continue for enough time.<\/p>\n

For example, the Atlantic Ocean between Nova Scotia and northwestern Africa has been getting wider at a rate of about 2.5 cm per year. Imagine yourself taking a journey at that rate \u2014 it would be impossibly and ridiculously slow. And yet, since it started to form around 200 Ma (just 4% of geological time), the Atlantic Ocean has grown to a width of over 5,000 km!<\/p>\n

A useful mechanism for understanding geological time is to scale it all down into one year. The origin of the solar system and Earth at 4.57 Ga would be represented by January 1, and the present year would be represented by the last tiny fraction of a second on New Year\u2019s Eve. At this scale, each day of the year represents 12.5 million years; each hour represents about 500,000 years; each minute represents 8,694 years; and each second represents 145 years. Some significant events in Earth\u2019s history, as expressed on this time scale, are summarized on Table 1.1.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Table 1.1\u00a0 A summary of some important geological dates expressed as if all of geological time was condensed into one year [SE]<\/caption>\n
Event<\/strong><\/th>\nApproximate Date<\/strong><\/th>\nCalendar Equivalent<\/strong><\/th>\n<\/tr>\n
Formation of oceans and continents<\/td>\n4.5 – 4.4 Ga<\/td>\nJanuary<\/td>\n<\/tr>\n
Evolution of the first primitive life forms<\/td>\n3.8 Ga<\/td>\nearly March<\/td>\n<\/tr>\n
Formation of British Columbia\u2019s oldest rocks<\/td>\n2.0 Ga<\/td>\nJuly<\/td>\n<\/tr>\n
Evolution of the first multi-celled animals<\/td>\n0.6 Ga or 600 Ma<\/td>\nNovember 15<\/td>\n<\/tr>\n
Animals first crawled onto land<\/td>\n360 Ma<\/td>\nDecember 1<\/td>\n<\/tr>\n
Vancouver Island reached North America and the Rocky Mountains were formed<\/td>\n90 Ma<\/td>\nDecember 25<\/td>\n<\/tr>\n
Extinction of the non-avian dinosaurs<\/td>\n65 Ma<\/td>\nDecember 26<\/td>\n<\/tr>\n
Beginning of the Pleistocene ice age<\/td>\n2 Ma or 2000 ka<\/td>\n8 p.m., December, 31<\/td>\n<\/tr>\n
Retreat of the most recent glacial ice from southern Canada<\/td>\n14 ka<\/td>\n11:58 p.m., December 31<\/td>\n<\/tr>\n
Arrival of the first people in British Columbia<\/td>\n10 ka<\/td>\n11:59 p.m., December 31<\/td>\n<\/tr>\n
Arrival of the first Europeans on the west coast of what is now Canada<\/td>\n250 years ago<\/td>\n2 seconds before midnight, December 31<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

\u00a0<\/strong><\/p>\n

\n
\n

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

\n

Exercise 1.4 Take a Trip through Geological Time<\/strong><\/p>\n

We\u2019re going on a road trip! Pack some snacks and grab some of your favourite music. We\u2019ll start in Tofino on Vancouver Island and head for the Royal Tyrrell Museum just outside of Drumheller, Alberta, 1,500 km away. Along the way, we\u2019ll talk about some important geological sites that we pass by, and we\u2019ll use the distance as a way of visualizing the extent of geological time. Of course it\u2019s just a \u201cvirtual\u201d road trip, but it will be fun anyway. To join in, go to: https:\/\/barabus.tru.ca\/geol2051\/road_trip\/road_trip.html<\/a><\/p>\n

Once you\u2019ve had a chance to do the road trip, answer these questions:<\/p>\n

1. We need oxygen to survive, and yet the first presence of free oxygen (O2<\/sub> gas) in the atmosphere and the oceans was a \u201ccatastrophe\u201d for some organisms. When did this happen and why was it a catastrophe?<\/p>\n

2. Approximately how much time elapsed between the colonization of land by plants and animals?<\/p>\n

3. Explain why the evolution of land plants was such a critical step in the evolution of life on Earth.<\/p>\n<\/div>\n<\/div>\n

  1. Hutton, J, 1788.\u00a0Theory of the Earth; or an investigation of the laws observable in the composition, dissolution, and restoration of land upon the Globe. Transactions of the Royal Society of Edinburgh. ↵<\/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-1981","chapter","type-chapter","status-publish","hentry"],"part":3150,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters\/1981","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\/1981\/revisions"}],"predecessor-version":[{"id":2991,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters\/1981\/revisions\/2991"}],"part":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/parts\/3150"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapters\/1981\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/media?parent=1981"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/pressbooks\/v2\/chapter-type?post=1981"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/contributor?post=1981"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/geology\/wp-json\/wp\/v2\/license?post=1981"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}