Of course, there is also a lot of water locked up as ice at the North and South Poles. Where all that water came from is a very good question. Scientists have been wondering about it for a long time. We are still not exactly sure but it is probably a combination of two places. Read more: Curious Kids: what started the Big Bang?
In the beginning, there was a huge cloud of dust and rocks in the Universe. Gravity caused the cloud to shrink and gradually the Sun and the planets formed. The original dust and rocks included minerals that had water in them. The Earth, as it formed, became very hot. It melted and there were lots of volcanoes.
The very existence of the Isua BIF requires the presence of stable surface water, at least locally for the chemical deposition of the sedimentary components at ca. These rocks were deposited in a somewhat analogous way to how limestones or cherts are deposited directly from seawater in modern marine environments. The oldest known Earth materials are actually not rocks. Sand grains comprised of the mineral zircon ZrSiO4 have been discovered that are almost million years older than the oldest rocks in the rock record.
Zircon is a very useful mineral that is mechanically resistant to erosion, chemically resistant to fluids, and can be 'dated' with the U-Pb method owing to the ubiquitous presence of trace amounts of radioactive U and Th that are incorporated in most zircons at the time of crystallization.
The very existence of these ancient zircons demonstrates that igneous rock e. But the evidence of oceans preserved in these grains comes in a different form.
Oxygen isotopes in geologic materials are affected by temperatures present during the formation and alteration of rocks and minerals. Analysis of oxygen isotope ratio in zircon can address the nature of the reservoir of oxygen in the magma that is adopted by the zircon during crystallization. Because we can also 'date' the zircon grains, we can place these conditions in a temporal context. Just after Ma the story changes. In other words, surface waters were present by at least Ma.
Hypothesis 1: Oceans first formed at ca. Hypothesis 2: Oceans formed much earlier by at least ca. The Jack Hills detrital zircons provide an actual timeline that records the magmatic oxygen isotope compositions of magmas on the young Earth.
In this regard, the detrital zircons actually record a boundary condition that marks when surface weathering, and hence the presence of oceans, occurred. Newsletter Get smart. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.
See Subscription Options. Discover World-Changing Science. Tobias C. Owen of the Institute for Astronomy in Honolulu, Hawaii, offers this overview: "This is a very good question, because we do not yet have an answer that everyone accepts. The salts include sodium chloride, magnesium chloride, and calcium chloride. Perhaps the most important substance dissolved in the ocean is salt. Everyone knows that ocean water tastes salty. That salt comes from mineral deposits that find their way to the ocean through the water cycle.
Salts comprise about 3. Depending on specific location, the salt content or salinity can vary. Where ocean water mixes with fresh water, like at the mouth of a river, the salinity will be lower. But where there is lots of evaporation and little circulation of water, salinity can be much higher. It is called the Dead Sea because so few organisms can live in its super salty water. The density mass per volume of seawater is greater than that of fresh water because it has so many dissolved substances in it.
When water is more dense, it sinks down to the bottom. Surface waters are usually lower in density and less saline. Temperature affects density too. Warm water is less dense and colder waters are more dense.
These differences in density create movement of water or deep ocean currents that transport water from the surface to greater depths. In , one of the deepest parts of the ocean 10, meters was reached by two men in a specially designed submarine called the Trieste Figure This part of the ocean has been named the Challenger Deep.
In contrast, the average depth of the ocean is 3, meters—still an incredible depth for sea creatures to live at and for humans to travel. What makes it so hard to live at the bottom of the ocean? There are three major factors—the absence of light, low temperature, and extremely high pressure. In order to better understand regions of the ocean, the scientists define different regions by depth Figure James Cameron repeated this feat in
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