The element
Earth
The science
There is no single thing called "earth." What the old four-element model lumped together, science pulls apart into rock, soil, and the chemistry of the planet's crust.
The crust is mostly oxygen and silicon, locked together as silicate minerals. Add aluminum, iron, calcium, sodium, potassium, magnesium, and you have nearly the whole of the ground under your feet by weight. Granite, basalt, sandstone, limestone. Stone is not dead and it is not permanent. It melts, it folds, it gets pushed up into mountains and worn back down to sand. The plates the continents ride on are still moving, a few centimeters a year, about as fast as your fingernails grow.
Soil is the living skin over that rock. Not just ground-up stone but a slow braid of minerals, water, air, and the dead. Fallen leaves, roots, bone, the bodies of countless small things, broken down by fungus and bacteria and worms into the dark crumbling stuff a seed can root in. A handful of healthy soil holds more living organisms than there are people on the planet.
So when you say "earth" you are really saying three things at once. The mineral bones of the crust. The living dirt that grows food. And the long, patient time it takes for one to become the other. Dust to dust is not a metaphor here. It is just the carbon cycle, told plain.
The meaning
Earth holds the suit of Pentacles, sometimes called Coins, sometimes Disks. The coin in the hand. This is the suit of the body and everything the body needs. Money, work, food, shelter, the garden, the craft you do with your hands, the long slow building of a life you can actually stand inside.
Its temperament is the one the old readers called melancholic. Cool, dry, slow, heavy. Not sad, though it can lean that way. More like the weight of a stone you can rely on. When Pentacles come up in a reading they pull the question down out of your head and into the real. Not what you feel about it, not what you fear. What it costs. What it grows. What you can touch.
Earth governs patience and the things that only ripen with time. A seed does not hurry. A debt does not vanish because you stopped looking at it. Read these cards as the part of the spread that asks, plainly, is this sustainable. Can you keep this up. Is the body fed.
In balance, Earth is the warm fact of having enough, the loaf on the table, the roof that holds the rain. Out of balance it tips two ways. Too little and you get scarcity, the cold worry, the never-quite-enough. Too much and it goes to stone, hoarding, stuck, a body that forgot it was supposed to also be alive. When this suit floods a reading, the gentle thing to ask is what you are holding that you could set down, and what you have been meaning to plant.