An endoskeleton made up of hard plates beneath the skin is a characteristic of the echinodermata phylum. Organisms under the phylum echinodermata have tight interlocking plates that form their endoskeleton. Sea urchins, starfishes and sea cucumbers are examples of echinoderms.
Answer:
The physical and chemical properties of seawater vary according to latitude, depth, nearness to land, and input of fresh water. Approximately 3.5 percent of seawater is composed of dissolved compounds, while the other 96.5 percent is pure water. The chemical composition of seawater reflects such processes as erosion of rock and sediments, volcanic activity, gas exchange with the atmosphere, the metabolic and breakdown products of organisms, and rain.
Explanation:
Answer:
4600-4500 million years ago, the Earth formed and its crust cooled to become solid. 4500-4400 million years ago, the oldest known thing to have formed on Earth, zircon, formed along with solid crust and oceans. 4200-4100 million years ago, the close of the Hadean Period (there are no surviving rocks).
