1700s, 1900s, 1950s, post-2000.
I see. I think you're wrong. Based on the Research Projects and actual widespread usage (instead of scientific discovery), we're looking at:
Modern: 1880s+ (WWI second tier)
Atomic: 1930s+: (interwar 1st tier, WW II second tier)
Information: 1960s+
1st tier Modern:
Electrical Revolution: 1870s+ (Empire State Building: 1931)
Modern Corporations: 1890ish
Statue of Liberty: 1886
Wire Services: 1850s
2nd tier Modern:
Plastics: 1930s
Cristo Redentor: 1931
Radio: 1920s
Multi-tier winged combat aircraft: 1914+ (Prora: 1939)
AA guns / machine guns / etc: 1912+
1st tier Atomic:
application of Penicillin: 1930s
electric refrigerators: 1927
fission research: 1930s
combined arms tactics: 1918 (Pentagon: 1943)
WWII era tanks: 1930s
2nd tier Atomic:
Electronics: ?? (mishmash of things that were in continuous development 1800s-1950s)
Computers: Late 1930s
Aircraft Carriers: 1930s
Bletchley Park: 1938
Bazooka: 1942
Atomic Bomb: 1945
Radar: 1940s
Single-wing aircraft (zeros, B17s etc): late 1930s
1st tier Information:
Sydney: Opera House: 1973
Recycling: 1970s
Solar Plants: 1970s
CN Tower: 1976
Telecommunications in general: 1920s
Satellites: 1960s
Apollo Program: 1960s
2nd tier Information
Jet Fighters: 1960s
Stealth Bombers: 1980-90s
Missile Cruisers: 1980s
Nuclear Subs: 1950s
Hubble Space Telescope: 1990
Internet: 1980s