The structures are thousands of kilometres wide and occupy 6% of the volume of the entire planet. Estimates of their heights vary, but one – found under Africa and known affectionately as "Tuzo" – is thought to be up to 800km (497 miles) high, equivalent to around 90 Everests stacked on top of each other. The second – "Jason", below the Pacific – might extend 1,800km (1,118 miles) upwards, translating to around 203 Everests. Their misshapen forms are moulded around the Earth"s core like two amoebas clinging to a speck of dust.