Richard Oldham didn't discover the Earth's outer core was liquid. That discovery was made through the analysis of seismic waves from earthquakes, not by any one person, but rather a culmination of observations and studies by several scientists over a period of time.

Here's a simplified timeline of how the discovery came about:

1. Early 1900s: Seismologists like Richard Oldham began studying seismic waves from earthquakes. They observed that these waves traveled through the Earth at different speeds and sometimes changed direction.

2. 1906: Oldham noticed a distinct "shadow zone" where certain seismic waves (S-waves) were absent on the opposite side of the Earth from an earthquake's epicenter. He suggested the Earth's interior must have a structure different from its crust.

3. 1914: Beno Gutenberg observed that P-waves (another type of seismic wave) slowed down significantly at a depth of around 2,900 kilometers (1,800 miles). This led him to propose the existence of a distinct boundary within the Earth.

4. 1936: Inge Lehmann, analyzing seismic waves, discovered that some P-waves were refracted back upwards from a depth of around 5,100 kilometers (3,200 miles). This pointed to the existence of a solid inner core surrounded by a liquid outer core.

Therefore, the discovery of the Earth's liquid outer core wasn't attributed to any single person, but was a gradual realization through the efforts of various seismologists analyzing seismic wave data over decades. Richard Oldham's contributions were significant in identifying early anomalies and laying the groundwork for future studies.