1870 through 1970 saw some amazing stuff invented. Take the transistor, for instance (invented, IIRC, in 1948). From that, we get these amazing chips with 4 GHz clock speeds, plus parallelism. It's all transistors...
... except that we didn't have such chips in 1970. We had, what, the Intel 4004?
That is, for things invented from 1870 to 1970, we have had at least 45 years of development after invention, and perhaps as much as 145 years of development, for those inventions to reach their full potential. Things invented in the last 20 years? Well, by definition, we haven't had more than 20 years of development after the invention. We're still where transistors were in 1968. At that time they were beginning to appear in radios, and had some use in mainframes, but there was no sign yet that they were going to completely dominate the world.
What could the current stuff be? Some AI techniques invented in the last 20 years could become huge. CRISPR might.
By the way, it's also kind of unfair to compare the amount of invention that occurred in 100 years to the amount in 20.