In the Western Pacific, south of Japan and north of New Guinea, and to the east of the Mariana Islands is the lowest elevation of the surface of the Earth's crust. Known as the Mariana Trench, the trench is nearly 1,580 miles (2,550 kms) long and 43 miles (69 km) wide, its deepest part is known as the Challenger Deep. Named after the Royal Navy ship, HMS Challenger that first sounded it back in December 1872 to May 1876, who recorded a depth of 31,614 feet, (9,636 metres).

Subsequent expeditions have lowered and raised the depth. In 1951, another Royal Navy vessel also called Challenger reported the depth as 35,761 ft, (10,900 m).

In 1957, the Russian vessel Vityaz reported a depth of 36,200 ft, (11,034 m).

In 1984, the Japanese reported a depth of 35,840 ft, (10,924 m)

Since then the National Geographic has published the maximum depth at 36,200 feet (11,034 metres) in 1995.

Also in 1995, the Japanese reported a depth of 35,798ft (10,911 m). This is thought to be the most accurate readings.

In June 2009, an American expedition reported the maximum depth of 35,994 ft (10,971 m).

In 2010, the US Center for Coastal & Ocean Mapping measured its depth at 36,070 ft (10,994 m).

So if we take the 1995 Japanese readings as the most accurate, that is 6.78 miles (10.91kms) straight down. If Mount Everest was placed there, its summit would still be one mile below the surface. The pressure down there is a staggering 15,966 pounds (7.24 metric tonnes) per square inch, or roughly 1,086 times the pressure we live with at sea level.

More men have walked on the Moon's surface than have visited the bottom. As of the time of writing (December 2009) only two men have visited the bottom, and that was back in 1960. Don Walsh and Jacques Piccard rode the bathyscape Trieste to the bottom, where they remained for 20 minutes. It looks like that record will stand for a long time, as no one has a manned DSV (that is in the public's knowledge) capable of reaching those depths.
Yes, the Mariana trench is the deepest trench, also not to be rude but it's trench not treanch.

First, scientists are pretty sure the Earth's core is about 80 percent iron. How they know that is a series of educated guesses.

For starters, they can be reasonably sure of the planet's mass based on its gravitational pull. The material on the surface isn't dense enough to match up with that mass, so the rest of the Earth has to be much denser.

It's a lot more scientific than I've made it sound, but hopefully that gets at the gist of it.

The Short Answer:

Some of it was here when the earth was made (but locked into the rocks as hydrates ... much of that released as the Earth became molten.)

And some came from comets and other ice particles that have bombarded the Earth since it was formed.

No one knows which part was the major contributor.

In more depth...:

At some early point in time (after the moon) the Earth was a hot, glowing ball which would have out-gassed fairly completely. Hydrogen is light enough so that most of it would have escaped. Free Hydrogen is lost from a planet as small as Earth, it takes the outer gas giants with much stronger gravitational pulls to hold it Additionally, there was little or no oxygen (all the bound oxygen was in the rocks - which is mostly still there).

One common theory of where the Earth's water comes from was the comet impact theory. The belief was that earths water came from comets that impacted on the early Earth (recall that at this time there would be no atmosphere to disintegrate the comets). Scientists have looked at samples of ice from comets and the ratios of heavy water (water with an isotope of hydrogen called deuterium) does not match the water found in the oceans. This has lead scientist to believe the oceans are not made up of mostly cometary water.

Evidence of water on the early Earth comes from Zircon Crystals dating from 4.53 billion years ago, only about 200 million years after the planet formed. Zircon crystals can only be created in the presence of water. This has lead scientist to believe that a large percentage of water was already in the rocks on Earth when it was created.

However examination from "fossil water" taken from Hawaiian volcanoes that originally comes from the bottom layers of the crust also shows differences from modern water.

A final note:

The following is a quote from the founder of Ask an Astronomer, Dave Kornreich:

No, H20 cannot exist in stars, but H and O separately can. Hydrogen is the basic building material of the universe, created in the Big Bang. Oxygen is created by nuclear reactions in stars. If you put H and O together in the cold of space, you get H2O. There are enourmous amounts of water in space. In fact, nearly all of the oxygen in space is in the form of water or carbon monoxide. Similarly, most the carbon and nitrogen in space are also in their most hydorgenated forms: methane (CH4) and ammonia (NH3).

Answer #1:

I believe you mean the Tropics of Cancer and Capricorn, but they are not half way (ie 45 degrees north and south) they are 23° 26′ 16″ N and S respectively.

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Answer #2:

I believe you mean the parallels halfway between the equator and the poles,

since that's the way you worded the question.

They are the parallels of 45° North latitude and 45° South latitude.

Deep time is the multibillion-year time frame that scientists believe Earth has existed. Their current estimate puts our planet at 4.54 billion years old.

Deep time’s hugeness, and especially the distance between events within it, is a trip to comprehend. Cleopatra, for instance, died in 30 B.C., but she lived closer to the present day than when the Pyramids of Giza were built.

If Earth’s history was represented on a 100-yard football field, modern humans—so Cleopatra, the pyramids, and everyone else—show up an eighth of an inch before the end zone. Heck, the length of deep time has an error range of 50 million years—but in the grand scheme of things, that’s small. Less than two yards on the football field.

Four Seasons, Winter. Seasons are a subdivision of a year. The Earth's rotation axis is tilted by 23.4392794383 degrees with respect to the, at different times of a variation in the 180 - 270 deg (mn), longitudes 270 - 360 deg (Winter). The Sun true longitude (Lsun) is derived from Sun mean longitude (Lmean) and Earth mean anomaly (ME). For any input through many Sun true Longitude (Lsun) for the input year 1013 :

1. Year = 2013, Start : UT year = 2013, month = 3, day = 20, hr = 11, min = 2, sec = 9.15719,true Log deg = 360.00000013, Start Time of: UT year = 2013, month = 6, day = 21, hr = 5, min = 1, sec = 23.88007, the Sun true Log deg = 90.00000: UT year = 2013, month = 9, day = 22, hr = 20, min = 45, sec = 38.50711, the Sun true Log deg = 180.00000
2. Year = 2013, Start Time of Winter : UT year = 2013, month = 12, day = 21, hr = 17, min = 10, sec = 7.88032, the Sun = 270.00000

Note : All these values are computed using the Orbital Mechanics - Model & Simulation Software OM-MSS.

Also all astronauts are able to read 50 shades of gay

p0rnhub.com

The cuboid.

or phalanges