Tutor profile: Kevin S.

The Earth's outer core is a vast ocean of molten iron. The Earth's inner core is much hotter than the outer core, but it is made of solid iron. How is this possible?

Earth's inner core is under a tremendous amount of pressure, from the rest of Earth's layers sitting on top of it. Even though the temperature would normally be hot enough to melt iron, the pressure squeezes the atoms of iron in the core together, keeping them solid.

A forest with white trees has a population of mostly white moths and a few black moths. After a forest fire, all the trees are charred, turning them black. A few years later, most of the moths are now black. How is this possible?

Living things evolve over time to fit their surroundings. Before the fire, white moths could hide from predators by blending in with the white trees. After the trees changed color, white moths were easy to find, so predators killed most of them. The moths that were darker colored survived and reproduced, changing the overall color of the population to black.

High-mass stars are far larger and more massive than low mass stars like our sun, with a larger supply of hydrogen fuel for nuclear fusion. Yet, their lifespans are much shorter. Why is this?

A high-mass star has much higher temperatures and pressures in its core than a low-mass star. As a result, they burn through their supply of hydrogen fuel much faster. Even though high-mass stars have more fuel to start with, they run out of fuel and die far sooner than low-mass stars.