Answer:
Many people believe that the world's 6th mass extinction has begun due to the rapidly increasing rate of species extinction that has been observed over the past few decades. Scientists estimate that species are currently going extinct at a rate that is 100 to 1,000 times higher than the natural background rate of extinction, which is the rate at which species would go extinct in the absence of human activities.
There are a number of factors that are driving this high rate of species extinction, including habitat loss and fragmentation, overexploitation of resources, pollution, climate change, and the introduction of invasive species. These factors are all related to human activities, such as land use changes, industrial activities, and the burning of fossil fuels.
Many scientists and environmentalists argue that these factors are leading to a global biodiversity crisis, which could have profound consequences for the functioning of ecosystems and the provision of ecosystem services that are essential for human well-being, such as food, clean water, and air.
Overall, the belief that the world's 6th mass extinction has begun is based on scientific evidence that indicates that the rate of species extinction is alarmingly high and is likely to continue to increase in the absence of effective conservation measures.