What is the main reason Earth's interior is liquid today?

The main reason Earth's interior, particularly the outer core, is liquid is due to the high temperatures and pressures found deep inside the planet. The Earth was formed through the accretion of particles and dust in the early solar system, and this process generated a significant amount of heat. Furthermore, radioactive decay of isotopes such as uranium, thorium, and potassium contribute to the ongoing production of heat within the Earth's interior. This heat melts the metals and rocks at certain depths, creating a liquid phase.

The Earth's outer core is primarily composed of iron and nickel and is in a liquid state because temperatures there exceed the melting point of these metals at the pressures present at that depth. Meanwhile, the inner core is solid despite being hotter than the outer core due to the even higher pressures that prevail there, which prevent the iron from melting.

The existence of this liquid outer core is also crucial for generating Earth's magnetic field through the dynamo effect, where the movement of the liquid iron alloy creates electrical currents that produce magnetic fields.