In the 1960s oceanography came up with some surprises. First of all, it was recognized that the ocean beds were not filled with miles and miles of sediment, as would be the case if the world's rivers had been carrying silt to the oceans for four billion years. Instead it was found that the ocean floors were geologically new.
Expansion
Image: Atlantic Floor Spreading
The second surprise was the discovery of the Atlantic ridges, a series of parallel ridges which run mostly north and south throughout the Atlantic. The ridges show a series of parallel magnetic reversals of the top layers of rock, matching east and west from approximately the center of the Atlantic. Further research has found the same in the Pacific and Indian ocean, although of a more complex pattern. Geological dates of the ridges also match from the center out. The oldest ocean beds are just east of China, with smaller stretches just off the North American east coast and in the south Caribbean. These regions all date from the Jurassic era, 200 to 150 million years ago.
It looked like the Earth had indeed been expanding, and in fact it looked like there were no oceans before the Jurassic. That means the original land mass (Pangea, the single land mass which had already been suggested as the parent to all of today's continents) must have covered all of the Earth at one time. The start of ocean floor spreading (as it is called) dates from after the first appearance of the giant dinosaurs during the Jurassic.
You can look at a globe and make some simple calculations. Subtracting the estimated spread of the Atlantic and Pacific from the current circumference of the Earth (25,000 miles) gives an earlier circumference of about 12,500 miles. The Earth had roughly doubled in diameter.
Gravity is a function of the mass divided by the square of the radius of the Earth. The mass of the Earth, assuming no change in density for the new material, is a cubic function of the radius. Thus gravity is linearly proportional to the radius of the Earth. As Earth expanded, gravity increased in proportion.