{"id":3325,"date":"2019-01-05T01:39:48","date_gmt":"2019-01-05T01:39:48","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/colorado-wmopen-geology\/?post_type=chapter&p=3325"},"modified":"2019-12-28T03:08:05","modified_gmt":"2019-12-28T03:08:05","slug":"how-do-we-know-the-age-of-earth","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/colorado-wmopen-geology\/chapter\/how-do-we-know-the-age-of-earth\/","title":{"raw":"Age of Earth: Early Efforts","rendered":"Age of Earth: Early Efforts"},"content":{"raw":"

No Shortage of Time<\/span><\/h2>\r\n
Image from Steven Earle, Physical Geology Open Text.<\/h6>\r\n\"\"<\/a>This time line is JUST the \"Phanerozoic\"-- the breakdown of time periods of the most recent 12% of geologic time, the last 540 million years.\u00a0 On some level, it's the \"fun\" part of geologic time, with abundant multi-cellular life, and life that contains skeletal parts or shells! Paleozoic is the time of life being abundant in the oceans, and the Mesozoic is the age of dinosaurs (plus a lot of other stuff!), and the Cenozoic is the age of mammals (plus a lot of other stuff!).\u00a0 But, to be fair, earth history and even the history of life (especially if one appreciates single celled organisms) goes much further back than 540 million years.\r\nIn fact, the bulk of geologic time is not shown on the above diagram, it's called the Precambrian, and it goes from 540 million years ago all the way back to 4,500 million years ago (i.e. the origin of the planet around 4.5 billion years).\r\n

The Puzzle of Fossils<\/span><\/h2>\r\nNowadays, if you show someone a fossil, they may not know exactly what sort of fossil it is, but they are very likely to be comfortable with the notion that it represents something that lived long ago, died, and was then buried by layers of sediment that eventually turned to rock!\r\n\r\nBefore the advent of science sometime in the mid-1600's, give or take a few years, things were different!|\r\nThere was actually a big debate--\r\n1) Maybe fossils represented past life, somehow frozen in rock.\u00a0 This is our modern idea.\r\nOR\r\n2) Maybe fossils were relicts of living things that were smashed into the rock as an aftermath.\r\nOR\r\n3) Maybe fossils were just examples of nature trying to growth life-like replicas \"within itself\"-- such that inanimate rock was trying to become \"animate\" and living!\r\n\r\nThe last one sounds pretty unusual, but before science there was a very blurred margin between the world of living and non-living things.\r\n\r\nWell, you know which side of the debate finally won out (yep, #1, above); and even though Leonardo da Vinci recognized that sea shells in mountainous rocks northeast of Genoa to represented an earlier period of low-lying land and inundation by seawater (and eventual uplift), it took well into the 18th century for our modern interpretation to become well established.\r\n
\"\"\r\nfrom Wikipedia,,\r\nJohann Jakob Scheuchzer<\/a> tried to explain fossils using Biblical floods in his Herbarium of the Deluge<\/i> (1709)<\/h5>\r\nLike so many great and important discoveries in science, the reigning models (theories or paradigms) did not explain newly discovered or observed features.\r\n<\/span>(See for example, Thomas Kuhn, The Structure of Scientific Revolutions, 1962.)<\/span><\/em>\r\nThe more people looked at not only fossils, but also rocks, the less sense it made to imagine all of earth's features created several thousand years ago and modified by catastrophic (e.g. Noah-type flood) events.\r\n<\/span>\r\n\r\n\"James This gentleman, James Hutton, who lived in Scotland in the mid- to late-1700's was uniquely both a wealthy farmer (landed gentry type) and a talented natural philosopher (that was the old name for scientists).\u00a0 He was part of the Scottish Enlightenment, and hung out with folks like the economist Adam Smith (author of the epoch treatise \"The Wealth of Nations) and the chemist Joseph Black (who discovered carbon dioxide and soda water) and the philosopher David Hume (who along with John Locke provided the formative ideas for a new nation that would be called the United States).\r\n\r\nHutton saw soil being washed away, and took the leap to recognize that mountains could also be washed away simply by giving the process enough time!\r\n\r\nHe also envisioned a world where uplift from the \"subterranean fires\" would serve to revive those eroding mountains and make more of them.\u00a0 He saw the world as having always behaved much the way it does today-- such that the processes of geological action from mountain uplift to erosion to sedimentation to volcanism, etc., have done so for a length of time so long that it would be hard to distinguish it from eternity!\r\nHe did get in a bit of trouble over \"eternity\" because just like a great vacation or bottle of wine, nothing lasts forever!\u00a0 He and his followers (e.g. Sir Charles Lyell) came to recognize the earth as a place that must be millions or even billions of years old.\r\n\r\nUniformitarianism<\/strong> is the term given to Hutton's belief in a world that probably behaved in the past, much as it does today.\r\nFrom the Oxford English Dictionary,\r\nUniformitarianism<\/em>=><\/strong>\u00a0 The theory that changes in the earth's crust during geological history have resulted from the action of continuous and uniform processes.<\/span><\/span><\/span>\r\n\r\n\"\"\r\n

Hutton's classic unconformity-- a result of deposition, tilting and renewed stratification,, Siccar Point Scotland<\/h3>\r\nHutton famously rowed a boat to a difficult to reach promontory on the coast of Scotland.<\/span>\r\nThere he saw rock that had been originally horizontal, tilted to nearly vertical orientation.<\/span>\r\nThese rocks were also overlain by younger flat-lying sediments.<\/span>\r\nHe recognized this to represent a time-gap, what we now call an unconformity.\u00a0 More on this to come!<\/span>\r\n\r\nAt the beginning of the next century (1800's) the geologist William Smith spent a huge amount of time mucking about England trying to help build canals, as part of the effort to move goods and materials all over the country.\u00a0 The canals were a key means to transport coal which was quickly becoming the required \"food\" for the industrial revolution.<\/span>\r\n\r\nSmith came to realize that the same sequences of rock layers were showing up all over the country.\r\nPart of the recognition came from looking at fossils, and led to what we might consider a rather simple idea today-- namely, the idea that different layers contained different fossils.\u00a0 Of course, the fossil changes were not exactly layer by layer, but it was becoming clear that one could identify older rocks versus younger rocks based on their contained assemblages of fossils.\u00a0 The idea became known as the principle of faunal succession.<\/strong>\r\n\r\nFaunal Succession is a principle, not really a theory, because it doesn't explain how or why these changes in fossils occur, from rock layer to rock layer.\u00a0 It's more of an observation.\r\nThe explanation of WHY these changes occur came later (not that much later, about 50 years) and was the work of a certain Charles Darwin.\r\n\r\nFaunal Succession helped Smith to keep track of the various layers.\r\nIt was an integral concept in generating the first a geological map of England, <\/span>published in 1815. <\/span>\r\n\r\nsee <\/span>http:\/\/en.wikipedia.org\/wiki\/William_Smith_%28geologist%29<\/a>\r\n\r\ncheck out the map on the Wiki page, and click on it for enlargement.\r\nEven if you forget about the science, it's beautiful in an artistic sense\r\n\r\n ","rendered":"

No Shortage of Time<\/span><\/h2>\n
Image from Steven Earle, Physical Geology Open Text.<\/h6>\n

\"\"<\/a>This time line is JUST the “Phanerozoic”– the breakdown of time periods of the most recent 12% of geologic time, the last 540 million years.\u00a0 On some level, it’s the “fun” part of geologic time, with abundant multi-cellular life, and life that contains skeletal parts or shells! Paleozoic is the time of life being abundant in the oceans, and the Mesozoic is the age of dinosaurs (plus a lot of other stuff!), and the Cenozoic is the age of mammals (plus a lot of other stuff!).\u00a0 But, to be fair, earth history and even the history of life (especially if one appreciates single celled organisms) goes much further back than 540 million years.
\nIn fact, the bulk of geologic time is not shown on the above diagram, it’s called the Precambrian, and it goes from 540 million years ago all the way back to 4,500 million years ago (i.e. the origin of the planet around 4.5 billion years).<\/p>\n

The Puzzle of Fossils<\/span><\/h2>\n

Nowadays, if you show someone a fossil, they may not know exactly what sort of fossil it is, but they are very likely to be comfortable with the notion that it represents something that lived long ago, died, and was then buried by layers of sediment that eventually turned to rock!<\/p>\n

Before the advent of science sometime in the mid-1600’s, give or take a few years, things were different!|
\nThere was actually a big debate–
\n1) Maybe fossils represented past life, somehow frozen in rock.\u00a0 This is our modern idea.
\nOR
\n2) Maybe fossils were relicts of living things that were smashed into the rock as an aftermath.
\nOR
\n3) Maybe fossils were just examples of nature trying to growth life-like replicas “within itself”– such that inanimate rock was trying to become “animate” and living!<\/p>\n

The last one sounds pretty unusual, but before science there was a very blurred margin between the world of living and non-living things.<\/p>\n

Well, you know which side of the debate finally won out (yep, #1, above); and even though Leonardo da Vinci recognized that sea shells in mountainous rocks northeast of Genoa to represented an earlier period of low-lying land and inundation by seawater (and eventual uplift), it took well into the 18th century for our modern interpretation to become well established.<\/p>\n

\"\"
\nfrom Wikipedia,,
\nJohann Jakob Scheuchzer<\/a> tried to explain fossils using Biblical floods in his Herbarium of the Deluge<\/i> (1709)<\/h5>\n

Like so many great and important discoveries in science, the reigning models (theories or paradigms) did not explain newly discovered or observed features.
\n<\/span>(See for example, Thomas Kuhn, The Structure of Scientific Revolutions, 1962.)<\/span><\/em>
\nThe more people looked at not only fossils, but also rocks, the less sense it made to imagine all of earth’s features created several thousand years ago and modified by catastrophic (e.g. Noah-type flood) events.
\n<\/span><\/p>\n

\"James This gentleman, James Hutton, who lived in Scotland in the mid- to late-1700’s was uniquely both a wealthy farmer (landed gentry type) and a talented natural philosopher (that was the old name for scientists).\u00a0 He was part of the Scottish Enlightenment, and hung out with folks like the economist Adam Smith (author of the epoch treatise “The Wealth of Nations) and the chemist Joseph Black (who discovered carbon dioxide and soda water) and the philosopher David Hume (who along with John Locke provided the formative ideas for a new nation that would be called the United States).<\/p>\n

Hutton saw soil being washed away, and took the leap to recognize that mountains could also be washed away simply by giving the process enough time!<\/p>\n

He also envisioned a world where uplift from the “subterranean fires” would serve to revive those eroding mountains and make more of them.\u00a0 He saw the world as having always behaved much the way it does today– such that the processes of geological action from mountain uplift to erosion to sedimentation to volcanism, etc., have done so for a length of time so long that it would be hard to distinguish it from eternity!
\nHe did get in a bit of trouble over “eternity” because just like a great vacation or bottle of wine, nothing lasts forever!\u00a0 He and his followers (e.g. Sir Charles Lyell) came to recognize the earth as a place that must be millions or even billions of years old.<\/p>\n

Uniformitarianism<\/strong> is the term given to Hutton’s belief in a world that probably behaved in the past, much as it does today.
\nFrom the Oxford English Dictionary,
\nUniformitarianism<\/em>=><\/strong>\u00a0 The theory that changes in the earth’s crust during geological history have resulted from the action of continuous and uniform processes.<\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Hutton’s classic unconformity– a result of deposition, tilting and renewed stratification,, Siccar Point Scotland<\/h3>\n

Hutton famously rowed a boat to a difficult to reach promontory on the coast of Scotland.<\/span>
\nThere he saw rock that had been originally horizontal, tilted to nearly vertical orientation.<\/span>
\nThese rocks were also overlain by younger flat-lying sediments.<\/span>
\nHe recognized this to represent a time-gap, what we now call an unconformity.\u00a0 More on this to come!<\/span><\/p>\n

At the beginning of the next century (1800’s) the geologist William Smith spent a huge amount of time mucking about England trying to help build canals, as part of the effort to move goods and materials all over the country.\u00a0 The canals were a key means to transport coal which was quickly becoming the required “food” for the industrial revolution.<\/span><\/p>\n

Smith came to realize that the same sequences of rock layers were showing up all over the country.
\nPart of the recognition came from looking at fossils, and led to what we might consider a rather simple idea today– namely, the idea that different layers contained different fossils.\u00a0 Of course, the fossil changes were not exactly layer by layer, but it was becoming clear that one could identify older rocks versus younger rocks based on their contained assemblages of fossils.\u00a0 The idea became known as the principle of faunal succession.<\/strong><\/p>\n

Faunal Succession is a principle, not really a theory, because it doesn’t explain how or why these changes in fossils occur, from rock layer to rock layer.\u00a0 It’s more of an observation.
\nThe explanation of WHY these changes occur came later (not that much later, about 50 years) and was the work of a certain Charles Darwin.<\/p>\n

Faunal Succession helped Smith to keep track of the various layers.
\nIt was an integral concept in generating the first a geological map of England, <\/span>published in 1815. <\/span><\/p>\n

see <\/span>http:\/\/en.wikipedia.org\/wiki\/William_Smith_%28geologist%29<\/a><\/p>\n

check out the map on the Wiki page, and click on it for enlargement.
\nEven if you forget about the science, it’s beautiful in an artistic sense<\/p>\n

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