The Earth’s core is cooling down very slowly over time. One day, when the core has completely cooled and become solid, it will have a huge impact on the whole planet. Scientists think that when that happens, Earth might be a bit like Mars, with a very thin atmosphere and no more volcanoes or earthquakes. Then it would be very difficult for life to survive – but that won’t be a problem for several billions of years.
Right now, the Earth’s core is not entirely molten. The inner core is a sphere of solid iron, while the outer core is made of molten iron thousands of kilometres thick.