16.How are rocks grouped within each unit of geologic time similar? 17. A unit of geologic time is usually characterized by
of a dominant life-form.
18. What does the abbreviation Ma stand for?
19. When did Precambrian time begin?
20. What species were common during the Cambrian Period?

Hydrilla (hydrilla verticillata) is an invasive aquatic plant and one of the most serious aquatic pests in florida. hydrilla has already been introduced to hundreds of bodies of water throughout florida, hydrilla is difficult to control because it grows rapidly and survives in many different water depths and conditions. hydrilla • describe how hydrilla affects native plant and animal species. include both a biotic and an abiotic limiting factor. • suggest one biotic and one abiotic recommendation that could slow the spread of hydrilla