Final answer:
Factors for population growth and decline. World population reaching 1 billion and doubling time.
Step-by-step explanation:
Population Growth and Decline
Population growth and decline are influenced by various factors. Some factors that account for population growth include birth rates, immigration, improved healthcare, economic development, and cultural beliefs. On the other hand, factors that contribute to population decline include death rates, emigration, disease epidemics, wars, and natural disasters.
World Population Reaching 1 Billion and Doubling Time
The world's population reached 1 billion around the year 1804. It took approximately 123 years for the population to double to 2 billion, reaching this milestone in 1927. This period is known as the doubling time.
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