The Earth's inner core is the Earth's innermost part. It is primarily a solid ball with a radius of about 1,220 kilometres (760 miles), which is about 70 % of the Moon's radius. It is composed of an iron -- nickel alloy and some light elements. The temperature at the inner core's surface is approximately 5,700 K (5,430 ° C), which is about the temperature at the surface of the Sun.\n\nBased on this passage, what is believed to be the composition of earth's core?
Stream of thoughts:
an iron -- nickel alloy and some light elements
The relevant information to answer the above question is: It is composed of an iron -- nickel alloy and some light elements.

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So, the final answer is an iron -- nickel alloy and some light elements