What is some evidence that earth's center is denser than earth's surface?

We know the surface of the Earth is made of rock, we can examine it ourselves. But what is the center of the Earth made of? Well, reach into your pockets and pull out some coins. That's roughly what the center of the Earth is made of.

The Earth is broken up into layers. The outermost layer is the crust - that's what you're standing on. About 30 km below your feet is where the next layer of the Earth, the mantle, starts. The mantle makes up the majority of the interior of the Earth, and its composed of heated rock under high pressure. But inside the mantle is the core of the Earth, and it's made of metal.

The Earth's core is broken up into two distinct regions. The inner core is a sphere of solid metal that measures about 2,440 km across. It's believed to be comprised of 80% iron and 20% nickel. Surrounding this solid inner core is an outer core of liquid metal that extends for approximately another 2,000 km. Geologists believe that the movement of metal in the outer core gives the Earth its magnetic field, allowing compasses to work.

Needless to say, the center of the Earth is incredibly hot. Scientists estimate that the core of the Earth could get as hot as 7,000 kelvin, and about 5,700 kelvin at the border between the inner and outer cores.

We've written many articles about the core of the Earth. Here's an article about how far down the center of the Earth is, and here's an article about the center of the Earth.

If you'd like more info on Earth, check out NASA's Solar System Exploration Guide on Earth. And here's a link to NASA's Earth Observatory.