1957-1961 Local interests dredged a channel across Padre Island and constructed two tetrapod jetties at the entrance to the Gulf of Mexico. The north and south jetties were 1,600 and 800 ft long, respectively, and spaced 1,000 ft apart.
The following four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this compresses the most recent eon. Therefore, the second scale shows the most recent eon with an expanded scale. The second scale compresses the most recent era, so the most recent era is expanded in the third scale.
The Richter Scale. Figure 1 - Charles Richter studying a seismogram. There are a number of ways to measure the magnitude of an earthquake. The first widely-used method, the Richter scale, was developed by Charles F. Richter in 1934. It used a formula based on amplitude of the largest wave recorded on a specific type of seismometer and the distance between the earthquake and the seismometer.