Final answer:
The decrease in biodiversity began with habitat destruction due to human activities such as farming, logging, and urban development, especially in biodiversity-rich areas like the Amazon rainforest. This has led to a current extinction rate much higher than the historical average, precipitating a biodiversity crisis.
Step-by-step explanation:
The decrease in biodiversity began primarily with habitat destruction driven by human activities. As the human population increases, the demand for resources leads to habitat loss, increased pollution, and climate change. These factors contribute to a higher rate of extinction and a subsequent decrease in biodiversity. Activities such as farming, logging, fishing, and the construction of roads and buildings facilitate habitat destruction. This is particularly evident in the loss of tropical rainforests like the Amazon, which are rich in biodiversity but are being cleared at an alarming rate for timber and agriculture.
Furthermore, biodiversity is more concentrated closer to the equator, and thus the destruction of habitats in these areas has a more significant impact on global biodiversity. The current extinction rate is estimated to be 500-1000 times higher than the background rate, indicating a biodiversity crisis. This rapid loss of biodiversity affects not only the known endangered species but also countless other species that have yet to be discovered by scientists, leading ultimately to a collapse of ecosystems that humans rely on for welfare.