History

#139 What are the six great mass extinction events?

I learned this today. There have been six mass extinctions on Earth that experts know about. The Great Oxidation Event about 2.4 billion years ago. The Ordovician-Silurian Extinction 440 million years ago. The Devonian Extinction 365 million years ago. The Permian-Triassic Extinction 250 million years ago. The Triassic-Jurassic Extinction 210 million years ago. The Cretaceous-Tertiary

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#130 Why do we have 24 hours in a day, 60 minutes in an hour, and 60 seconds in a minute?

I learned this today. We have 24 hours in a day because of Hipparchus. We have 60 seconds in a minute and 60 minutes in an hour because of Claudius Ptolemy, Al-Biruni, and the Babylonians. Before we look at this topic, we have to remember that needing to know the time exactly is a fairly

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