Why do apples go brown, and why aren’t the oceans warmer?

We explore some of the curious questions that science can answer

The brown fruit can be una-peel-ing but is perfectly safe to eat (Getty/iStockphoto)

Why do apples go brown?

When you cut an apple you’re actually bursting open the cells that make up the apple. This releases an enzyme called phenoloxidase. This enzyme takes oxygen from the air and adds it to a chemical in the apples called tannin.

When oxygen and tannin are bound together, the tannin turns brown. Cooking or chilling the apple will stop it from turning brown. Vitamin C also stops apples from turning brown because it grabs the oxygen from the air before it can react with the tannin.

How was the Giant’s Causeway (on the coast of County Antrim, Northern Ireland) formed?

The 40,000 hexagonal basalt columns are about 55 million years old and were formed by cooling lava. As basalt lava flows cool, it slowly solidifies. The top and the bottom of the lava flow are cooled respectively by the air and by the rock over which it has flowed, while the interior is insulated and remains hot. So the upper and lower surfaces harden first. As the lava on the surface cools, it hardens at randomly scattered centres. Basalt shrinks as it solidifies, so the solid area spreads slowly out as ever-increasing circles. At an equal distance between any two, the solidifying basalt will be pulled in as it shrinks, forming a crack. The cracks will be roughly hexagonal over the whole surface, though they vary quite a bit. It’s the same principle as hexagonal cracks forming in mud where a puddle has just dried up. As the interior of the lava cools, the cracks deepen.

What are cobwebs?

Cobwebs are made from silk. The silk is spun through the end of the spider’s abdomen rather like toothpaste being squeezed out of a tube. The silk is produced from special glands inside the spider – a female spider can produce seven types of silk. Sometimes a spider will eat its old web and recycle the silk. Spider silk is incredibly strong – almost as strong as Kevlar, the material used to make bulletproof vests.

If the centre of the Earth is so hot, why isn’t the ocean warmer?

You are right to say that the centre of the Earth is extremely hot – about 4,300C. But it is a long way from the core to the surface, and the temperature falls the nearer to the surface you get. All things considered, the ocean is quite warm, while the Earth’s crust can be quite cool if it isn’t near a volcanic area.