7 objects made by humans that are thought to be creations of nature

When life give you lemons... As it turns out, life would never give us lemons if it wasn't for us. Lemons are not naturally occurring – they are hybrids of citron and bitter orange. Telling the truth, most citrus fruits we know and love are hybrids: natural citruses are only the pomelo, papeda, mandarin, and citron.

Dogs are our best friends, but where do they come from? There are no wild dogs – the species of animals named "African wild dogs" doesn’t belong to the same family as our pets. The closest relative of dogs is the extant gray wolf, which was domesticated by prehistoric people, which resulted in the emergence of dogs as we know them today 20,000-30,000 years ago.

Most diamonds found in stores are natural, but, in fact, synthetic diamonds made in labs look the same to the naked eye. They are grown by placing carbon under high pressure and high temperature, which forms a diamond crystal. Are there any significant differences between natural and man-made diamonds? Well, the ones created by nature are more than 3 billion years old, while synthetic ones are quite "young".

Just like diamonds, pearls can be manufactured. Anyway, while most diamonds we can buy are natural, pearls created without human intervention are extremely rare. Pearls grown on farms make up almost 100% of the pearls available on the market.

The smell of gas we use in household is not natural. This distinct odor is added for us to detect gas leaks. In nature, such gases are odorless.

This word is a combination of "smoke" and "fog", and while fog is a natural phenomenon, smog has nothing to do with it. Smog is visible air pollution which is caused by industrial and vehicular emissions.

This area is often seen as an environment untouched by humans, but many modern scientists believe that the Amazon Basin had been altered by millions of people who lived there for more than 8,000 years. Some parts of today's rainforest have only grown a few centuries ago, when the ancient civilizations were wiped out by the Europeans.