<story><title>Earth’s innermost layer is a 644 kilometer wide ball of iron, new study finds</title><url>https://www.archyde.com/earths-innermost-layer-is-a-644-kilometer-wide-ball-of-iron-new-study-finds/</url></story><parent_chain><item><author>jofer</author><text>Mantle plumes don&amp;#x27;t significantly change the shape of the core or mantle, though. They&amp;#x27;re convection within the mantle. They rise from the core mantle boundary, but they&amp;#x27;re basically temperature features, not structural features.&lt;p&gt;In other words, mantle plumes are parts of the mantle that are hotter than the other identically composed mantle around them.&lt;p&gt;In contrast, the core and the crust are different compositions than the mantle.&lt;p&gt;Just to clear up another common confusion, the mantle is very much solid, except for a tiny fraction of melt in a narrow and shallow zone called the athenosphere. The mantle flows over time despite being solid, though (think of a glacier). Just like a marble slab will bend over time (see benches in old graveyards that sag in the middle), the mantle slowly flows, but a hammer&amp;#x2F;etc would bounce right off of it.  That&amp;#x27;s also true of large portions of the crust.&lt;p&gt;As far as how smooth or not smooth the actually core boundaries are, we don&amp;#x27;t really know in detail. To a first order, they&amp;#x27;re smooth (i.e. we measure a broadly consistent radius from multiple directions), but that doesn&amp;#x27;t mean they&amp;#x27;re necessarily a &amp;quot;billard ball&amp;quot;.  There&amp;#x27;s likely fairly complex topography at the boundary that we can&amp;#x27;t easily measure.</text></item><item><author>LeifCarrotson</author><text>This article shows the layers of the Earth as being perfectly spherical, like the oblate spheroid that is the top layer of Earth&amp;#x27;s crust. Little 8km high Everest mountain ranges or 8km deep Mariana trenches are peach fuzz on the 12,750 km diameter billiard ball, and I suppose it seems reasonable to assume that the mantle and core beneath are similarly shaped by gravity to near-perfect spheroids.&lt;p&gt;But I recently learned about the African and Central Pacific mantle plumes, which rise far above the circles in those Pac-man renderings:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.theatlantic.com&amp;#x2F;science&amp;#x2F;archive&amp;#x2F;2020&amp;#x2F;01&amp;#x2F;seismic-mystery-underneath-africa-and-pacific&amp;#x2F;604729&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.theatlantic.com&amp;#x2F;science&amp;#x2F;archive&amp;#x2F;2020&amp;#x2F;01&amp;#x2F;seismic-...&lt;/a&gt;&lt;p&gt;I expect that&amp;#x27;s old news to someone in the field, but I haven&amp;#x27;t thought critically about that diagram since high school.</text></item></parent_chain><comment><author>nine_k</author><text>If you take a real well-played snooker ball, it has plenty of tiny but visible scratches, say, 0.25 mm deep.the ball&amp;#x27;s diameter is 52.5 mm, so the scratches depth is about 1&amp;#x2F;200 of its diameter. If we take Earth&amp;#x27;s diameter as 12750 km, scratches like that would be features about 63 km tall, nearly an order of magnitude larger than tallest mountains on Earth. If course the mantle is smaller diameter, but unless we cannot detect roughly 50  km-tall ridges (I don&amp;#x27;t know much about seismic wave registration), it&amp;#x27;s about as smooth as a billiard ball %)</text></comment>
<story><title>Earth’s innermost layer is a 644 kilometer wide ball of iron, new study finds</title><url>https://www.archyde.com/earths-innermost-layer-is-a-644-kilometer-wide-ball-of-iron-new-study-finds/</url></story><parent_chain><item><author>jofer</author><text>Mantle plumes don&amp;#x27;t significantly change the shape of the core or mantle, though. They&amp;#x27;re convection within the mantle. They rise from the core mantle boundary, but they&amp;#x27;re basically temperature features, not structural features.&lt;p&gt;In other words, mantle plumes are parts of the mantle that are hotter than the other identically composed mantle around them.&lt;p&gt;In contrast, the core and the crust are different compositions than the mantle.&lt;p&gt;Just to clear up another common confusion, the mantle is very much solid, except for a tiny fraction of melt in a narrow and shallow zone called the athenosphere. The mantle flows over time despite being solid, though (think of a glacier). Just like a marble slab will bend over time (see benches in old graveyards that sag in the middle), the mantle slowly flows, but a hammer&amp;#x2F;etc would bounce right off of it.  That&amp;#x27;s also true of large portions of the crust.&lt;p&gt;As far as how smooth or not smooth the actually core boundaries are, we don&amp;#x27;t really know in detail. To a first order, they&amp;#x27;re smooth (i.e. we measure a broadly consistent radius from multiple directions), but that doesn&amp;#x27;t mean they&amp;#x27;re necessarily a &amp;quot;billard ball&amp;quot;.  There&amp;#x27;s likely fairly complex topography at the boundary that we can&amp;#x27;t easily measure.</text></item><item><author>LeifCarrotson</author><text>This article shows the layers of the Earth as being perfectly spherical, like the oblate spheroid that is the top layer of Earth&amp;#x27;s crust. Little 8km high Everest mountain ranges or 8km deep Mariana trenches are peach fuzz on the 12,750 km diameter billiard ball, and I suppose it seems reasonable to assume that the mantle and core beneath are similarly shaped by gravity to near-perfect spheroids.&lt;p&gt;But I recently learned about the African and Central Pacific mantle plumes, which rise far above the circles in those Pac-man renderings:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.theatlantic.com&amp;#x2F;science&amp;#x2F;archive&amp;#x2F;2020&amp;#x2F;01&amp;#x2F;seismic-mystery-underneath-africa-and-pacific&amp;#x2F;604729&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.theatlantic.com&amp;#x2F;science&amp;#x2F;archive&amp;#x2F;2020&amp;#x2F;01&amp;#x2F;seismic-...&lt;/a&gt;&lt;p&gt;I expect that&amp;#x27;s old news to someone in the field, but I haven&amp;#x27;t thought critically about that diagram since high school.</text></item></parent_chain><comment><author>ASalazarMX</author><text>&amp;gt; Just like a marble slab will bend over time (see benches in old graveyards that sag in the middle), the mantle slowly flows&lt;p&gt;I had to see more of this, and it took me a while because most results are about construction and marble products. It looks like thin slabs of marble bow because of microfractures and internal stress, not by flowing.&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;link.springer.com&amp;#x2F;article&amp;#x2F;10.1007&amp;#x2F;s00254-008-1307-z&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;link.springer.com&amp;#x2F;article&amp;#x2F;10.1007&amp;#x2F;s00254-008-1307-z&lt;/a&gt;</text></comment>