If an asteroid created enough dust to block out the Sun, it would likely have a severe and devastating effect on life on Earth.
Green plants, which rely on sunlight for photosynthesis, would not be able to produce the energy they need to survive, leading to mass die-offs of vegetation. This would in turn have a cascading effect on the entire ecosystem, as animals that depend on plants for food would also struggle to survive. The lack of sunlight would also cause a decrease in temperature, which can have a negative impact on many organisms.
The lack of sunlight would also have a severe impact on the climate and weather patterns, leading to a "nuclear winter" scenario, where the temperature drops significantly, leading to the extinction of many species, including the human species, who rely on the food chain.