Why is it Hot Underground?YouTube↗  IA↗(long shot)
Science & Technology  7M views 63.2K likes 4.5K dislikes   16 Jul 2014
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Way back in the Middle Ages, miners began to notice that the deeper they dug into the
قديمًا في العصور الوسطى، لاحظ عمال المناجم أنه كلما حفروا بشكل أعمق في
earth, the toastier it got. Who knows what they made of the heat, but the physicist Lord
الأرض، كلما أصبحت أشد حرارة. لا أحد يعلم كيف لهم تحمل الحرارة. لكن اقترح العالم الفيزيائي
Kelvin - of temperature fame, naturally - had a theory: Earth started off hot, and has been
لورد كلفن -الذي سميت الوحدة باسمه- نظرية وهي: بدأت الأرض ساخنة،
cooling down ever since, like a baked potato pulled from the oven. What's more, Kelvin
لكنها تبرد منذ ذلك الحين، كالبطاطا المشوية بعد الفرن. وعلاوة على ذلك،
was confident this idea would allow him to calculate the age of our potat-- planet...
كان كلفن واثقًا بأن هذه الفكرة ستتيح له حساب عمر البطاط....أعني الكوكب
Imagine pulling two recently-baked potatoes out of a freezer - one that's been in there
تخيل أنك أخرجت بطاطتين مطبوختين من الثلاجة، تركت إحداهما
for just one minute, the other for half an hour. The minute-old-one would still feel
لدقيقة فقط، والأخرى لنصف ساعة. ستكون التي تركتها لدقيقة
like a hot potato, while the half-hour frozen spud would have cooled well below the skin
ملمسها كالمطبوخة، بينما الثانية التي تركتها لنصف ساعة سيبرد جوفها
— you'd have to poke all the way to the center to feel its residual warmth. And so
وسيتوجب عليك النخر الى وسطها للشعور بحرارتها المتبقية.
in principle, you can tell how long ago a potato was cooked just by feeling how warm
ومن حيث المبدأ، يمكنك معرفة متى تم طبخ البطاطا بقياس الحرارة
it is right beneath its surface.
تحت قشرتها.
Which is exactly what Kelvin did - except with the earth. And scientific rigor. He took
وهذا بالضبط ما فعله كلفن، غير أنه طبقها على الأرض، باستخدام القياسات العلمية.
temperature measurements from the mines, put them into his calculations and, got... 20
فقد أخذ قياسات الحرارة من المناجم، ووضعها في حساباته وتوصل بأن عمر الأرض يساوي
million years.
20 مليون سنة.
Which is, of course, very, very wrong — somehow, the hot temperatures just under Earth's skin
وذلك بالطبع خاطئ جداً. بطريقة ما، أوهمت درجات الحرارة تحت قشرة الأرض
made it seem, to Kelvin, that our planet was pretty much fresh out of its cosmic oven,
كلفن بأن الارض قد خرجت طازجة من فرنها الكوني.
when we now know that it's four and a half THOUSAND million years old.
بينما نعلم الآن أن الأرض عمرها 4.5 الف مليون سنة.
Kelvin's error is usually attributed to the fact that he didn't know about radioactivity,
ويرجع خطأ كلفن إلى أنه لم يعلم بوجود النشاط الإشعاعي،
which creates a ton of heat in Earth's core and helps keep the planet warm. But heat from
إذ أنه ينتج حرارة بكميات هائلة في باطن الأرض ويساهم في المحافظة على دفء كوكبنا. لكن تتحرك الحرارة الناتجة من
radioactive decay moves so slowly through solid rock that taking radioactivity into
انحلال النشاط الأشعاعي بشكل بطيء عبر الصخور الصلبة حتى أنه لو
account only improves Kelvin's estimate by... pretty much nothing.
أخذ بها بالحسبان، لن تتحسن نتائجه كثيرًا.
Kelvin's real oversight was in thinking of the Earth like a baked potato — a solid
خطأ كلفن الحقيقي كان في تفكيره بأن الأرض كالبطاطا المشوية
lump through which heat slowly diffuses. Earth's mantle — the thick layer between the crust
-ككتلة صلبة تنشر الحرارة ببطء- ويعد أغلب لب الأرض - وهو الطبقة السميكة بين القشرة
and the core — is mostly solid, but it isn't rigid. In fact, the rock closest to the molten
و النواة- صلبًا، لكنه غير جامد. في الحقيقة، تصبح الصخرة الأقرب إلى
outer regions of the core gets so hot that it becomes slightly more pliable, like warmed
الجهات الخارجية من النواة شديدة الحرارة لدرجة أنها تصبح أكثر قابلية للثني
candle wax. And like the hot air above a candle, the warm rock rises in convection currents
كالشمع. وكمثل الهواء الساخن فوق الشمعة، تصعد الصخرة الساخنة في تيارات النقل
- over millions of years - spreading heat more evenly throughout the planet. This stirring
على مدى الملايين من السنيين- وتقوم بتوزيع الحرارة بالتساوي عبر الكوكب. وهذا التحرك
carries tremendous amounts of heat from the core to the crust, fueling volcanoes, maybe
يحمل كمية ضخمة من الحرارة من نواة الأرض إلى القشرة، وذلك يمد البراكين بالطاقة،
helping to drive plate tectonics, and heating mine shafts to temperatures that make Earth
وربما يساعد على تحريك الصفائح التكتونية و يقوم أيضًا بتسخين المناجم إلى درجات حرارة تجعل الأرض
seem like it's fresh out of the cosmic oven.
تبدو كأنها خرجت للتو من فرنها الكوني.
Even though it's not.
حتى لو لم تكن كذلك.
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