Każdy z nas kojarzy rafę koralową z pięknymi kolorowymi strukturami zwierząt w pięknych ciepłych wodach tropików.

Chyba nikt nie jest w stanie sobie wyobrazić podobnych struktur w głębiach oceanu, gdzie jest ciemno, a do tego bardzo zimno. Taki pogląd funkcjonował aż do drugiej połowy XX wieku. Wtedy zaczęto przeprowadzać badania z użyciem pojazdów podwodnych.

Ku wielkiemu zaskoczeniu naukowców okazało się, że w głębinach oceanu też znajdują się rafy koralowe. Są rozbudowanymi strukturami o wysokości dochodzącej do 100 metrów. Występują w głębinach Arktyki i Antarktyki, na zboczach wysp, szelfów kontynentalnych, wygasłych wulkanów, grzbietach oceanicznych. Woda w której występują ma temperaturę 0-12 stopni Celsjusza. Rafy zimnowodne występują zwykle występują na głębokości 200-2000 metrów p.p.m.

Koralowce są domem dla ryb, mięczaków, skorupiaków itd. Do tej pory zidentyfikowano około 4 tysiące gatunków głębinowych koralowców. Niektóre są malutkie jak ziarenko piasku, ale są też bardzo okazałe gatunki dorastające do 6 metrów wysokości, takie jak gorgonia Paragorgia arborea. Wygląda ona jak krzak zbudowany z nadmuchanej gumy balonowej.

Obecnie największą odkrytą zimnowodną strukturą jest ta u wybrzeży Norwegii. Rafa Rost ma około 3 kilometrów szerokości i 40 kilometrów długości. Z datowania węglowego wynika, że jej wiek to około 8 tysięcy lat. Zaczęła się budować po ustąpieniu ostatniej epoki lodowcowej.

Izotopy promieniotwórcze w medycynie

Zjawisko promieniotwórczości zostało odkryte jako całkowity przypadek przez Henri Becquerela podczas jego badań naukowych w roku 1896. Nikt wtedy nie podejrzewał, że za kilkadziesiąt lat będzie to narzędzie w diagnostyce i leczeniu.

Pierwszym radioizotopem użytym w medycynie był rad. Odkryty przez małżeństwo Curie, zastosowany został pierwszy raz do leczenia pewnych rodzajów nowotworów narządów rodnych przez ginekologa Howarda Atwooda, pracującego na John Hopkins University. Niestety rad jest silnie radioaktywny i jego zastosowanie przynosiło więcej szkody niż korzyści, więc szybko wycofano go z użycia.

Od tego czasu odkryto wiele izotopów promieniotwórczych, szeroko stosowanych w diagnostyce oraz terapii.

Najbardziej popularnym izotopem jest jod, pierwiastek kluczowy dla prawidłowego funkcjonowania tarczycy. W naturze jod-127 jest jedynym trwałym izotopem tego pierwiastka. Pozostałe (jod-123, 124, 125, 131) są promieniotwórcze i to one są stosowane w diagnostyce i leczeniu tarczycy.

Jednym z bardziej popularnych badań tarczycy jest scyntygrafia, do której wykorzystuje się jod-123. Polega to na wprowadzeniu do organizmu odpowiednich radiofarmaceutyków, czyli preparatów medycznych znakowanych izotopami promieniotwórczymi. Następnie wykonuje się obrazowanie za pomocą gammakamery i ona rejestruje promieniowanie emitowane przez dany narząd. Natomiast jod-124 wykorzystuje się do pozytonowej tomografii emisyjnej zwanej PET.

Kolejnym promieniotwórczym izotopem wykorzystywanym w medycynie jest kobalt. Od kilkudziesięciu lat wykorzystywany do leczenia jako tzw. bomba kobaltowa. To efekt uboczny pracy nad bombą atomową.

Terapię kobaltem zaczęto stosować w Kanadzie w latach 50. ubiegłego wieku. Ze względu na duże wytwarzanie odpadów radioaktywnych obecnie coraz częściej zastępuje się ją akceleratorami liniowymi, które emitują podobne promieniowanie, ale nie generują tyle niebezpiecznych odpadów.

Najstarszy falochron ma aż 7 tysięcy lat

Falochron to konstrukcja, która ma za zadanie chronić port, promenadę lub inną nadbrzeżną konstrukcję przed działaniem fal. Rozbija fale i nie dopuszcza do rozmycia przez nie nabrzeża.

Międzynarodowa epika naukowców odkryła falochron w miejscowości Tel Hreiz na wybrzeżu Karmel w Izraelu. Został on zbudowany 7 tysięcy lat temu przez neolitycznych mieszkańców.

Falochron zbudowany był z głazów i miał długość 100 metrów. Głazy sprowadzono z odległości około 4 kilometrów.

W czasie neolitu populacje śródziemnomorskie były narażone na zalania, gdyż wzrost poziomu morza wynosił około 4-7 mm rocznie, co w ciągu 100 lat daje wysokość 70 centymetrów.

Dr Ehud Galili z Uniwersytetu w Hajfie powiedział: „Systematyczny wzrost poziomu morza wymusił na ludziach budowę wału nadmorskiego, który przypomina współczesne falochrony z całego świata”.

Prehistoryczne Tel Hreiz wybudowano na wysokości 3 metrów n.p.m. Wybudowany wał nie wystarczył na długo, w późniejszym okresie wioska została opuszczona i zalana.

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