How does the inner core affect earth?
The inner core affects the earth in a number of ways, due to its incredibly high density and temperature.
How It Started:
As the earth was being formed, it accumulated increasing mass as particles and lumps and meteoroids and asteroids and increasingly larger bodies were drawn in by earth's ever increasing gravity.
As the gravity increased, the denser component material was drawn to the center of the earth to form the inner core of mostly iron and nickel with heavy metals added. As the inner core grew, it also substantially increased its temperature as the gravitational force squeezed the metals tighter together with tremendous force. There were nuclear reactions occurring at the same time, further increasing the temperature.
With the heavy inner core, the earth's orbit and rotation will remain stable over the long term, giving us day and night and summer and winter. The earth's spin, started as large bodies collided with or were added to its structure, will continue until a collision with a very large space object (asteroid or larger) occurs. It was a collision with a large space object that gave the earth its tilt, and four seasons for the temperate climate zones.
The intense heat of the inner core is keeping the outer core a dense liquid that contains convection currents due to the heat, and they are directed by the earth's spin. The inner core is also believed to be moving at a different rate than the outer core. These swirling convection currents result in the earth's magnetic field which keeps us properly oriented for travel, and shields earth from deadly cosmic rays.
There is more information here: