MATH IN GEOLOGY
What is geology?
The word “geology” comes from the Greek geo,meaning “the Earth,” and the ology
suffix comes from logos,meaning “discussion.” Overall, geology is considered to be the
study of the Earth. In modern times, thanks to space probes reaching into the solar sys-
tem, geology also now entails the surface features on other planets and satellites.
Who first made some of the first accurate measurementsof the Earth?
Hellenic geographer, librarian, and astronomer Eratosthenes of Cyrene (276–194 BCE)
made several accurate measurements of the Earth, which is why he is often known as
the “father of geodesy” (the science of Earth measurement). Although he was not the
very first to deduce the Earth’s circumference, Eratosthenes is thought by most histo-
rians to be the first to accurately measure it.
Eratosthenes knew the Sun’s light at noon reached the bottom of a well in Syene
(now Aswan on the Nile River in Egypt) (meaning the Sun was directly overhead) on
the summer solstice. He compared it to a well’s shadow at the same time in Alexan-
dria. Knowing that the zenith distance (the angle from the zenith [point directly over-
head] to the point where the Sun was at noon) was 0 degrees at Syene, this meant that
at Alexandria it was about 7 degrees. By measuring these angles and the distance
between the two cities, Eratosthenes used geometry to deduce that the Earth’s cir-
cumference was 250,000 stadia. The number was later revised to 252,000 stadia, or
25,054 miles (40,320 kilometers).
The actual circumference of the planet is 24,857 miles (40,009 kilometers) around
the poles and 24,900 miles (40,079 kilometers) around the equator, because the Earth 295
MATH IN THE
NATURAL
SCIENCES