Clues such as fossils such as bones, footprints, tar, etc, preserved underground helped inform scientists. You can also count how old a tree is when you cut it open and there are some alive for thousands of years so that is a possible way.
Answer:
Our water resources face a host of serious threats, all of which are caused primarily by human activity. They include sedimentation, pollution, climate change, deforestation, landscape changes, and urban growth.
Phosphates generally come from fertilizer, erosion of phosphate-containing rocks. they are fertilizers, so they tend to strongly encourage growth, particularly of bacteria and algae. This can harm ecologies, particularly in water, and particularly where there isn't a very robust growth medium already, e.g. in cold or desert waters.<span>This impacts the environment and our health because we use tap water for cooking, bathing, brushing teeth, and etc. and these water by be contaminated because of all of this pollution going around</span>
