I believe it is the 1990s.
long period of time before people developed systems of writing and a written language
There wasn't really a 'time period' of Nationalism . It began as each country developed its own identity .
Prehistory
The Flute was developed over a long period of time-the MiddleAges! It was developed so the player could have a wider range of melody.
Although consumption over this time period grew from 33.7 million metric tons to 58.9 million metric tons, production declined from 60.7 million metric tons to 38.7 million metric tons
You can use the defect density metric to track the number of defects found over a period of time. Defect density is calculated by dividing the total number of defects by the size of the software, usually measured in lines of code or function points. This metric helps in identifying trends in defect discovery and can inform quality improvement efforts.
long period of time before people developed systems of writing and a written language
metric unit of time is called a second.
The metric unit of time is the second.There isn't one in common use but:10 metric hours in a day100 metric minutes in a metric hour100 metric seconds in a metric minute10 days in a metric week (called a dekade)
The metric unit for snowfall is typically measured in centimeters (cm) or millimeters (mm). Snowfall is commonly reported as the depth of snow that accumulates over a specific area during a specific period of time.
Albert Einstein's h-index, a metric used to measure the impact and productivity of a scientist's research output, is not applicable as it was developed after his time.