|The fault in our stars|
The Expanding Earth hypothesis, first proposed by Robert Mantovani in 1889, attempts to explain continental drift, but without the actual continental drift.
This hypothesis was actually considered not unreasonable before the acceptance of plate tectonics, and there have been a small number of older respectable geologists who held it plausible. It defied physics, but the geologists had been right and physics and chemistry wrong in the 19th century regarding the age of the Earth, and the geologists still had a great big smug on. These days, though, it's cranks all the way down.
The hypothesis posits that the Earth is growing as a result of the expansion of the seafloor. According to its proponents, an "expanding Earth" model explains why the outlines of continents that were separated by continental drift do not quite match up (most people cite erosion as the major cause of this). If the Earth were, say, 20% smaller, it is claimed that South America and Africa would fit together like pieces in a jigsaw puzzle..
There are several versions of the hypothesis, from one that claims that the Earth's mass has remained constant (and surface gravity has therefore decreased), to another that holds that the Earth's mass has increased (where the extra mass came from is completely unaccounted for), to yet another that holds that the gravitational constant of the Universe has changed.
Problems with the hypothesis
As mentioned above, the idea of an expanding Earth has several problems and very little evidence to back it up. For instance, in continental drift theory, we have measurements of the rate of plate movement (done by fancy satellites and lasers) that show the speed of movement. This movement, projected back, gives us the last time the continents were together. That these figures match up with geological strata and the fossil record is another big hint that we have this right.
Although some observations that lead to continental drift can also — by a stretch of the imagination — be explained by an expanding Earth, no positive evidence exists that the Earth is expanding. The issue as to whether the Earth has increased in mass (and where it came from) if gravity changed (and how) and if the Earth's density is altering are still issues that the expanding-Earth idea fails to address. How the concept fits in with the development of the Solar System is also unknown, as presumably other planets and moons would also undergo expansion if it was possible; alternatively, one would need to explain why the Earth, and only the Earth, expands. If, at some point of the past, the radius of the Earth had been 50% of its current value, gravity force would be in the order of 39m/s², a value that would crush most humans, let alone bigger creatures like dinosaurs. Also, Earth density would work out at 44 kg/l, a value far exceeding that of the most dense materials on the planet. Modification of the gravity constants would have equally catastrophic effects, related to the orbit of the Earth around the Sun.
The "theory" also utterly fails to explain places where plates are crashing into each other — most notably, the creation of the Alps and the Himalayas due to the African and Indian plates, respectively, moving north and encountering the (relatively) immovable object of Eurasia.
The most prominent current advocate is superhero comics artist Neal Adams, who is otherwise a sound enough fellow and does great comics but has just this little bit of batshittery. He posits new mass being created by electron-positron pair production in the core of the Earth, stating that the pair production's positron can somehow become protons, making hydrogen atoms in the process. One of the greatest flaws in his argument is his belief that science is either deliberately deceiving the public or that the entire system of science is wrong and that it must change to adhere to his "theory" (actually nothing more than speculation without evidence).
There is apparently a group called the Growing Earth Consortium.