March 3, 2024

I, Science

The science magazine of Imperial College

From the 19th century onward, it was well established that the coastlines of continents showed an uncanny resemblance to each other.

This created the possibility that they had once existed as an unbroken landmass named Pangea, from the Greek for “whole Earth”. However, some coastlines fitted far from perfectly, leaving large gaps between certain continents.  In 1933, Otto Hilgenberg realised that if the Earth was less than half its current size, the continents would fit perfectly to form an unbroken shell. This led him to propose the “Expanding Earth” theory; that the Earth had once existed in a much smaller state, and had gradually grown to its current size.

According to Hilgenberg, the Earth began it’s life a mere 22,000 km in circumference. Growing at around 6cm/year, it reached its current size of 40,000 km approximately 200 million years later.

Despite providing an attractive account of continental drift, the expanding Earth theory failed to stand up to any sustained scrutiny. No account was made to explain the emergence of extra matter, and it could not explain why the Earth has shown no further expansion in its 4.6 billion year old life. Additionally, it lacked a feasible mechanism for providing the huge force needed drive the expansion against the force of gravity. A radial increase of just 20% would require more energy than is contained within the chemical bonds of all matter on Earth. Put simply, it is impossible.  Advocates claimed that the laws of nature may have changed during this period of expansion, making energy concerns irrelevant. Thankfully, this last ditch attempt to legitimise expansionist claims was quashed with the emergence of plate tectonic theory in the 1970s, which states that convection currents created by super-heated magma are responsible for continental drift.

So, when you next use the phrase “it’s a small world”, remember that if Hilgenberg were right, long ago it could have been a whole lot smaller.