In many ways, the floor of oceans is no better explored than space. Why could discoveries such as life around deep-sea hotspots not be investigated until the past few decades?

3 answers

What is a robot?
A good way to research your answer to this question would be to do a search on recent advances in marine technology. What is the technology used for? Knowing this, you can write about how it provides something that previous technology did not.
Imaginary example: Google entry -- super bubble probe 2012. This machine allows for bubble-specialists to examine bubbles at sub-microscopic levels. This probe has a lens that can magnify to a magnitude of xyw. No other bubble probe has ever had the capacity to examine at these magnitudes, allowing bubble-specialists from 2012 unprecedented frontier breaking advances in bubble research.
Visit websites of periodicals like sciencemag or discover magazine, and have a look through their subject lists for marine-related articles.