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invertebrate #pollinators, especially bees & face extinction.
The goal is to strengthen protections for bees to help protect food security & #biodiversity. Something that gives me hope is seeing how much of a difference individuals are making: making pollinator gardens, planting native species, protecting ecosystems and spreading knowledge. These are things even the very young can do. 🧵2/2
May 20 is World Bee Day. There are ~20,000 different bee species in the world. Here in Ontario we have at least 400 native bees (none of which are the honeybees, which are from Europe). Bees are key to pollination. According to the UN nearly 90% of the world’s wild flowering plant species depend, entirely, or in part, on animal pollination, along with more than 75% of the world’s food crops. Further, worldwide ~35% of 🧵
She later also discovered the Lehmann discontinuity in the mantle. When she received the Bowie medal in ‘71 (1st woman to receive the highest honour of the AGU), her citation noted that the “Lehmann discontinuity was discovered through exacting scrutiny of seismic records by a master of a black art for which no amount of computerization is likely to be a complete substitute...”. 🧵5/5
That means, the p-waves from an earthquake can be recorded at seismic stations out to 105° from an epicentre & there is a zone which is in the core’s shadow. Lehmann found that there were some late-arriving P-waves are much larger angles (142 to 180°) which had been vaguely labelled ‘diffractions’. She showed that these could be explained instead by deflections of the waves which travelled through the outer core at her postulated inner core boundary.
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through different media, these seismic waves can bend, reflect or be transmitted at any boundary. The difference in physical properties between the mantle & outer core causes a P-wave shadow. (For S-waves, the shadow zone is absolute because liquids, like outer core, do not support shear - imagine trying to cut water with a pair of shears and you can see this for yourself. Thus, no shear waves can make it through the outer core, & thus we can be certain the outer core is fluid). 🧵3/
The crust, on which we live is merely a thin scum on top of this slowly boiling pot. The only way to probe deep into the core is to employ massive earthquakes. There are 2 main types of seismic waves used: Primary (or P, or compressional) & Secondary (or S, or shear). Imagine a glass of water with a straw; the straw will appear broken at the air-water interface, because light bends as it enters the water. Just like light travelling 🧵2/
Happy birthday to Danish #seismologist Inge Lehmann (1888 – 1993) who demonstrated that the Earth’s core is not a single molten sphere, but contained an inner solid core, in ‘36. She was a pioneer #womanInScience, a brilliant seismologist & lived to be 105.
As she first postulated, the earth has roughly 3 equal concentric sections: mantle, liquid outer core & solid inner core. 🧵