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Post by Moose on Jun 16, 2017 20:29:56 GMT
I've decided to learn the history of the earth, starting with the Paleoproterozoic era which is as far back as I can find. Now, everyone find me one fact about this era, and you're not allowed to use wiki.
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Post by Moose on Jun 16, 2017 20:30:23 GMT
Okay there were apparently only 20 hours a day during this period? Why?
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Post by Moose on Jun 16, 2017 20:44:47 GMT
Hmm I can't find out very much else about this era ... am on Mesoproterozoic now . Much more hospitable, cos there was oxygen.
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Post by Moose on Jun 16, 2017 20:47:43 GMT
Apparently sexual reproduction started at this point .. not not a great deal else.
Neoproterozioc now.
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Post by tangent on Jun 16, 2017 20:48:37 GMT
Okay there were apparently only 20 hours a day during this period? Why? Because tides have caused the earth's rotation to slow down.
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Post by Moose on Jun 16, 2017 21:24:32 GMT
Is that still going on?
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Post by tangent on Jun 16, 2017 21:36:38 GMT
Yes, every 50,000 years the day becomes one second longer.
In the Paleoproterozoic era, the moon was very much closer to the earth and tides had an enormous effect. But since then, the moon has gradually receded from the earth and so the length of day is changing only very slowly.
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Post by Moose on Jun 16, 2017 21:41:32 GMT
cool!
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Post by JoeP on Jun 16, 2017 22:23:32 GMT
Technically, this isn't HISTORY - which is when people wrote stuff down - it's PREHISTORY.
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Post by Moose on Jun 16, 2017 23:07:12 GMT
*removes head from the Jurassic for long enough to say .. oh, shurrup*
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Post by tangent on Jun 17, 2017 3:41:57 GMT
The earliest era (or eon) is the Hadean when the earth was formed (4600 to 3900 million years ago). The most significant event in that eon occurred when a Mars sized body, called Theia, crashed into the earth and formed the moon. See www.ayton.id.au/gary/History/H_PreH1.htm for a list of eons and era.
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Post by Moose on Jun 17, 2017 16:48:16 GMT
Cool thank you!
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Post by jayme on Jun 18, 2017 14:44:53 GMT
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Post by tangent on Jun 18, 2017 17:20:42 GMT
million
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Post by Moose on Jun 18, 2017 20:02:07 GMT
Gotta go with Steve on this one
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Post by JoeP on Jun 19, 2017 11:10:07 GMT
4600 to 3900 million years ago = 4.6 to 3.9 billion years ago, American billion
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Post by ceptimus on Jun 19, 2017 15:46:33 GMT
The American billion does make sense really, and the old British billion is dead in the water.
I only realized recently that all the ***-illion words you hear bandied about do make some sort of sense with the same prefixes used for multiple births (triplets, quadruplets, quintuplets, ...) counting the groups of three digits before the hundreds, tens, and units:
thousand = 1,000 million = 1,000,000 (from the Roman mile meaning 'one thousand' - i.e. a thousand thousands) billion = 1,000,000,000 trillion = 1,000,000,000,000 (three groups of '000' to count the number of thousands) quadrillion = 1,000,000,000,000,000 (four groups) quintillion = five groups sextillion = six groups septillion = seven groups
...and then it goes oct, non, dec, and so on up to increasingly useless words for big numbers where it's much easier to say something like 'ten to the fifteen'.
...so each of the -illion words is for a number a thousand times bigger than the one before, starting with million as 'a thousand thousands.'
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Post by tangent on Jun 19, 2017 17:30:59 GMT
... although googol, which is 10 to the power 100, doesn't exactly follow the trend.
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Post by jayme on Jun 19, 2017 23:55:23 GMT
Yeah. I meant American billion. The one with the decimal points you forgot to type.
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Post by tangent on Jun 20, 2017 6:59:19 GMT
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Post by Alvamiga on Jun 20, 2017 18:48:15 GMT
4600 to 3900 million years ago = 4.6 to 3.9 billion years ago, American billion Milliard!
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Post by ceptimus on Jun 20, 2017 20:08:12 GMT
Are we ready to move on to the Neoarchean era yet? I think that was the one with the first proper photosynthesising plants causing the atmosphere to have abundant oxygen for the first time.
Oxygen was a waste product of the photosynthesis process and it was originally very poisonous and toxic to living things - but as the concentration of oxygen gradually built up, life had to learn to accommodate it and eventually came to depend on it.
Oxygen is still a very dangerous and reactive gas, of course: it allows things to catch fire! It's just that we're so used to it and so dependent on it that we don't realize how weird it is. If we find evidence of oxygen on other worlds we can be confident that there is life there. In the absence of life any oxygen would quickly be used up (quickly in the astronomical or geological context) as it reacts with virtually everything so ends up bound in various types of rock and minerals.
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