By the 1850s ships had been crossing the Earth’s oceans regularly for 200 years and the coastlines of Earth’s main landmasses had already been surveyed. But little was known about the sea beyond a depth of a few tens of metres.
Scientists reasoned that beyond 500m deep the seas must be totally lifeless because of the darkness, high pressure and intense cold.
There were two main reasons why pressure grew in the 1850s and 1860s to explore the deep ocean.
Firstly, small scientific expeditions in the North Sea and around Scandinavia found evidence of life deeper in the oceans than ever before, below 1km. The deep sea might not be lifeless after all.
These expeditions found life forms that were new and unfamiliar. Some of them were living fossils – creatures thought to have gone extinct millions of years ago. They looked similar to the animals of an ancient world more than to other animals living at the time.
Scientists had read Darwin's theory of evolution and some thought that ancient life forms continued to exist at the bottom of the sea. This idea caused a lot of excitement.
There was also economic pressure to explore the deep sea. Companies wanted to lay submarine cables for communication between Europe and America by telegraph, but to do this they needed accurate knowledge of the shape and nature of the deep sea floor.
It was time to explore the oceans further, both for scientific and commercial reasons.