If 50% of a radioactive element remains after 4000 years what is its half-life?

20 points asap! question 1 - in your own words, explain the scientific evidence that supports the plate tectonic theory. question 2 - in your own words, explain why the geological structures in florida are different from the geological structures in colorado.

Dan made the table shown to describe two different relationships between animals. organism interactions relationship a relationship b one organism lives inside the organism it feeds off no organism is harmed which of the following statements is most likely correct?

24. how are vaccines used to keep people healthy?