Science & Mathematics How did the ocean begin?

[DeadlyAkkuret]

I'm sure a science buff can help me out with some theories on this one. Aplologies if this seems like a stupid question, but was it always just.....there?

 

[cats2rise]

Baby Jesus' tears.

 

[DeadlyAkkuret]

So that's where the Jesus Wept saying comes from.

 

[TigerGlory]

God did it.

If this was on my RE exam... 10/10.

 

[PunyHumans!!!]

Probably impacting asteroids and proto planets which were icy could have deposited some amounts of water, escaping gasses from volcanic activity, the creation of an atmosphere and the beginning of the formation of rain clouds. Something like that. This would have happened relatively early in the earth's life, around 4.4 billion years...the planet itself may have actually been a watery world and not a fiery, magma riddled hell hole...I am not scientist myself, that's just I can understand from reading rather large and confusing words.

 

[Monster]

Ice asteroids, over several million years, during the early part of earths history

during this time the earth was impacted far more than it is today.

 

[Caesar]

The short answer is that nobody's really sure. Aside from the aforementioned asteroid impact theory, there's also speculation that atmospheric pressure during the earth's cooling phase led to water being retained (wheras on other planets it was lost), or that photodisassociation resulted in radioactive breakdown of more complex compounds to form H2O.

There are a couple of other theories but they're the main ones I remember.

 

[BomberGal]

I watched a documentary on this on the plane back from Europe the other week.

Unfortunately, as I'd been on the plane for 21 hours, I remember very little. What I do remember is that the asteroid theory has been discredited - at least to provide any substantial amount of water. Radioactive analysis of water in asteroids has shown that the water in them is not the same as the water on earth.

 

[Pie eyed]

4 billion years ago, the Earth could be described as a very large, hot rock without a trace of water on its surface. Water on the young Earth came from two sources, outgassing from within the Earth and bombardment by comets. Outgassing is the process whereby gases are released from molten rock in the mantle of the planet by volcanic activity. This was probably the primary source of gases for the early atmosphere. Comets and meterorites also bring with them gases which contributed to the Earth's atmosphere.
Some of the gases in the new atmosphere were methane (CH3), ammonia (NH3), water vapor (H2O), and carbon dioxide (CO2). The water on Earth stayed in gaseous form until the planet's surface cooled below 100 degrees Celsius. At this time, 3.8 billion years ago, water condensed into rain and poured onto the land. Water collected in low lying areas which gradually became the primitive oceans.
As water entered the oceans from the atmosphere, it brought with it dissolved gasses released from the mantle by volcanoes and geysers. Water also flowed as runoff from the land, bringing in dissolved minerals from the rocks on the surface. These minerals include the salts which make seawater taste salty.

http://www.chem.duke.edu/~jds/cruise_chem/oceans/ocean1.html

 

[DeadlyAkkuret]

Some really great info so far guys, thanks to everyone who's posted something helpful

 

[The Sultan]

watched a doco on foxtel on how the earth was created and from memory the theory was......

the earth was originally molten rock (or something like that) and as it cooled over billions of years it produced gases the gases rose but couldn't escape the earths atmohere (due to gravity??), as these gases built up chemical reaction created hydogen and oxygen (then formed water particles it then began to rain and did so for for millions of years ie as it rained it cooled the moten quicker which produced steam which is term created more rain. as mentioned this cycle continued for millions of years until the earths crust was cooled, and the water settled where erosion and tatonic (sp?) plates had shifted creating oceans and from the oceans single cells microisms formed and from there life was created.

that was a very laymans description and im not sure if i even got it right

 

[Pie eyed]

watched a doco on foxtel on how the earth was created and from memory the theory was......

the earth was originally molten rock (or something like that) and as it cooled over billions of years it produced gases the gases rose but couldn't escape the earths atmohere (due to gravity??), as these gases built up chemical reaction created hydogen and oxygen (then formed water particles it then began to rain and did so for for millions of years ie as it rained it cooled the moten quicker which produced steam which is term created more rain. as mentioned this cycle continued for millions of years until the earths crust was cooled, and the water settled where erosion and tatonic (sp?) plates had shifted creating oceans and from the oceans single cells microisms formed and from there life was created.

that was a very laymans description and im not sure if i even got it right

Accurate enough.

 

[BomberGal]

Accurate enough.

Assuming the oxygen formed in the rocks, not in the atmosphere...?

 

[smiths]

It was just there when humans were formed, why do you have to be so difficult?

 

[Matthew2708]

The asteroid theory seems right.
But quite far in the future, the ocean will start boiling and then it will evaporate completely.

 

[BomberGal]

The asteroid theory seems right.

Except that it's been shown to be implausible?

 

[Pie eyed]

Assuming the oxygen formed in the rocks, not in the atmosphere...?

Strangely enough Oxygen (O2) only appeared in any quantity after Water (H2O).

The following elements were the result of volcanis out gassing H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 (ammonia) and CH4 (methane).
Oxygen is not found in volcanic gases.

It is explained here:

Addition of O2 to the Atmosphere

Today, the atmosphere is ~21% free oxygen. How did oxygen reach these levels in the atmosphere? Revisit the oxygen cycle:

• Oxygen Production
  • Photochemical dissociation - breakup of water molecules by ultraviolet
    • Produced O2 levels approx. 1-2% current levels
    • At these levels O3 (Ozone) can form to shield Earth surface from UV
  • Photosynthesis - CO2 + H2O + sunlight = organic compounds + O2 - produced by cyanobacteria, and eventually higher plants - supplied the rest of O2 to atmosphere. Thus plant populations
• Oxygen Consumers
  • Chemical Weathering - through oxidation of surface materials (early consumer)
  • Animal Respiration (much later)
  • Burning of Fossil Fuels (much, much later)

Throughout the Archean there was little to no free oxygen in the atmosphere (<1% of presence levels). What little was produced by cyanobacteria, was probably consumed by the weathering process. Once rocks at the surface were sufficiently oxidized, more oxygen could remain free in the atmosphere. During the Proterozoic the amount of free O2 in the atmosphere rose from 1 - 10 %. Most of this was released by cyanobacteria, which increase in abundance in the fossil record 2.3 Ga. Present levels of O2 were probably not achieved until ~400 Ma.

http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html

The asteroid theory seems right.
But quite far in the future, the ocean will start boiling and then it will evaporate completely.

About the time the earth was formed, the sun became large enough that the fusion reactions in the sun ignited. This didn't happen smoothly, but likely in sputtering way for a while. Each flaring up of the sun sent streams of particles sweeping out. If the earth had an atmosphere at this time, it would have been blown off leaving the earth as a rock with neither air or water on its surface. In fact, after the sun stabilized, the earth went through a process of releasing gases from its interior in a process called degassing. Over a relatively short time, something like a 100 million years, enough material had been released to form the oceans and to give the earth an atmosphere. There was no free oxygen in the atmosphere at this time, but it was a collection of gases, largely ammonia, methane and carbon dioxide, held to the earth by gravitational attraction. Fortunately, early in its history, the temperature of the earth dropped below 212 degrees Fahrenheit, and the water condensed into the oceans we know today. In fact, the mass of water present in the oceans, now about 10(24) grams, is about the same as the mass of water that was contained in the crust when the degassing process started.

Asteroids could have only contributed a very small amount of water after formation of the earth as could comets, however technically a large proportion of the accreted matter which formed the earth could be considered to be asteroids so it just depends on you view point.

 

[DeadlyAkkuret]

After reading these theories it's hard to come to any other conclusion than our existence being one big fluke.

 

[BomberGal]

Strangely enough Oxygen (O2) only appeared in any quantity after Water (H2O).

Either way, I mean the oxygen can't have been free in the air, because atmosphere oxygen levels were quite low for a very long time.

 

[Pie eyed]

Either way, I mean the oxygen can't have been free in the air, because atmosphere oxygen levels were quite low for a very long time.

Until the explosion of plant life.

 

[BomberGal]

Until the explosion of plant life.

Photosynthesising cyanobacteria actually