1) The construction of the Great Wall of China began in the 7th century BC and was completed over several centuries, spanning thousands of miles.

2) The Earth's core is primarily composed of iron and nickel and is as hot as the surface of the sun.

3) The ancient city of Athens, Greece, is often considered the birthplace of democracy, where citizens had a say in the decision-making process.

4) Male seahorses are the ones who give birth to their offspring.