On this timeline, there are 10 years between each date on the timeline, therefore the interval is 10 years. You can also think of it as "We're counting by 10 years." What interval is being used on each timeline? The span of a timeline is the amount of time from the beginning to the end of the timeline.
Ya it is real because we are living in a same planet every thing is linked with each other. it was the great hypothesis of the world one does pollution and all of us have to face it .