The One Minute Geographer: This Fragile Earth (1) Size of the Earth

Jim Fonseca
2 min readFeb 1, 2022
Image from nineplanets.org

This is the first in a series of posts about the Amazing Fragility of Our Earth — Thus Fragile Earth for short.

Actually our earth is quite large compared to us tiny humans, and it initially looks like we are the fragile ones. So let’s look at the size of the earth first.

The earth is huge actually — averaging about 24,880 miles in circumference. Let’s call it 25,000. Have you ever driven 500 miles in a day? (Was that fun?) Anyway, if you could drive the circumference of the earth at the Equator — ignoring oceans and impassable mountains, not to mention the lack of roads — just think: you’d be on the road for 50 days!

Diagram from laulima.hawaii.edu

It turns out the earth is not a perfect sphere; thus we talk about average circumference. It’s an ‘oblate ellipsoid,’ like a beach ball squished at the top and bottom, bulging a bit in the middle. That’s ‘middle age spread’ from the centrifugal force of the earth’s rotation pushing material out. It’s not much of a bulge — the earth’s diameter is only about 25 miles fatter through the equator than at the poles, but we’ll see later that the bulging has an impact when we talk about the height of mountains.

The earth’s diameter averages 7,918 miles — call it 8,000. Suppose it were possible to take an elevator through the center of the earth from North Pole to South Pole. How long would that take you? (While you are waiting for the elevator at the pole and it feels chilly, don’t worry, it will warm up later in the trip.)

Well it turns out that fast elevators operating today can reach 20 mph. In a 24-hour day you can cover 480 miles. You’ve got to go 8,000 miles. Do the math: 8,000/480 = almost 17 days of continuous travel locked in that elevator! (Bring snacks and plastic garbage bags.)

Here’s the next post in the Fragile Earth series:

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Jim Fonseca

Geography professor (retired) writes The One Minute Geographer featuring This Fragile Earth. Top writer in Transportation and, in past months, Travel.