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In 1936 the Danish seismologist Inge Lehmann used earthquake waves to show that the Earth's core has two parts: a solid inner core inside a liquid outer core.

Inge Lehmann

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The story behind the card

Lehmann, a seismologist (a scientist who studies earthquakes and the waves they send through the Earth), headed the seismology department of Denmark's Geodetic Institute from 1928. Scientists then thought the core was a single ball of molten metal, which should bend certain waves away and leave a 'shadow zone' on the far side of the planet where they could not arrive. Studying records of a large 1929 earthquake in New Zealand, she noticed strong waves reaching stations in Russia that lay inside that zone. Her explanation was a smaller, solid core at the centre that reflects the waves. Leading seismologists accepted it within a few years, and computer calculations confirmed it in 1971. The inner core stays solid, despite temperatures similar to the Sun's surface, because of the enormous pressure. Lehmann died in 1993, aged 104.

Türkçe oku
Danimarkalı sismolog Inge Lehmann, 1936'da deprem dalgalarını inceleyerek Dünya'nın çekirdeğinin iki bölümden oluştuğunu gösterdi: sıvı bir dış çekirdeğin içinde katı bir iç çekirdek vardır.

Deprem bilimci (sismolog) Lehmann, 1928'den itibaren Danimarka Jeodezi Enstitüsü'nün sismoloji bölümünü yönetiyordu. O yıllarda çekirdeğin tümüyle erimiş metalden bir küre olduğu düşünülüyordu. Böyle bir çekirdek bazı dalgaları saptırmalı ve gezegenin öbür yüzünde bu dalgaların ulaşamayacağı bir “gölge bölgesi” bırakmalıydı. Lehmann, 1929'da Yeni Zelanda'da olan büyük bir depremin kayıtlarını incelerken bu bölgenin içinde kalan Rusya'daki istasyonlara belirgin dalgalar ulaştığını fark etti. Açıklaması şuydu: merkezde, dalgaları yansıtan daha küçük ve katı bir çekirdek vardı. Önde gelen sismologlar bu açıklamayı birkaç yıl içinde benimsedi; 1971'de bilgisayar hesapları da doğruladı. İç çekirdek, Güneş'in yüzeyine yakın sıcaklığa rağmen muazzam basınç yüzünden katı kalır. Lehmann 1993'te, 104 yaşında öldü.

Sources and further reading

Background reading: Inge Lehmann
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