The theory that convection currents in the mantle move the continents was put forward in the 1930s by:

In the late 1920s and 1930s, the British geologist Arthur Holmes proposed that convection currents in the Earth's mantle could provide the force needed to move the continents.

The problem Holmes tried to solve:

The continental drift theory, proposed in 1912, suggested that the continents had moved over time.

But it could not explain what force was strong enough to move huge continents. The forces suggested, such as tidal force and a force related to the Earth's rotation, were far too weak.

Many geologists therefore rejected the idea.

Holmes's convection current theory:

Heat is produced inside the Earth by the decay of radioactive elements such as uranium, thorium and potassium.

This heat causes the material in the mantle to move very slowly in circular currents, called convection currents. Hot material rises, spreads out, cools and sinks again.

Where currents rise and move apart beneath a continent, they could stretch and split the continent, forming a new ocean between the parts.

Where currents meet and sink, they could drag down the crust and build mountains.

Significance:

• Holmes's theory was ahead of its time and was not widely accepted until the 1960s.
• It became an important foundation for the later ideas of sea-floor spreading and plate tectonics.

Other contributions of Arthur Holmes:

He was a pioneer in using radioactive decay to date rocks (radiometric dating).

In 1913, he estimated the age of the Earth to be about 1.6 billion years, later revising it upward. This helped establish that the Earth is billions of years old.

Mantle convection today:

• Modern geologists agree that mantle convection is part of the driving force for plate motion.
• They also emphasise "slab pull", in which the heavy, sinking edge of a plate pulls the rest of the plate along, and "ridge push".

Why not the other options?

• ✗James Hutton (18th century) is called the father of modern geology.
• ✗Eduard Suess, an Austrian geologist, wrote "The Face of the Earth" and introduced the term biosphere.
• ✗Charles Lyell, in the 19th century, popularised uniformitarianism, the idea that present processes explain the past.