How it all started | Marine Biology
The Earth is over 70% water, our oceans are the home to many interesting, unique and undiscovered species. So far, we have discovered barely 5% of our oceans, we have hardly scratched the surface! But how did we end up with such lively and splendid oceans?
Well, we all know that our solar system formed from the collapse of a large cloud of dust and gas. At the centre of this cloud, a dense ball of gas ignited to form the Sun. The unstable star unleashed many fierce solar winds (mainly electrons and protons). Over time this stream of charged particles pushed the remaining gas cloud farther and farther out, leaving only solid particles behind to clump together into rocks, planetesimals, and finally, the rocky planets of our solar system.
The problem is that water, in the form of ice, couldn’t have been one of the solid particles that stuck around because the early inner solar system was too hot for frozen water, and any water vapour would have been blasted away by the solar wind. We know water was not created on Earth over the eons, because processes like combustion, breathing and photosynthesis create and destroy roughly equal amounts of water, and either way, the amounts in question are so miniscule that they cannot be accounted for the abundance of water on the planet. Hence, the only explanation could be, that it travelled through space and landed on Earth through meteoroids, comets or other bodies that originated from the outer solar system, where they were far enough for frozen water to survive.
Comets were a very likely source of water originating on Earth, but were ruled out when it was discovered that comets were far richer in heavy hydrogen; a hydrogen atom with a proton and a neutron in its nucleus. For every million hydrogen atoms in water, about 150 of them were heavy hydrogen. A comet however, contained roughly about twice that number of heavy hydrogens. These mismatched chemical signatures suggest that Earth’s water could not have arrived on comets.
The most likely source of our water would have been a meteorite called a carbonaceous chondrite. These meteorites contained a lot of water and carbon. They had water in them as they formed outside the sun’s “frost line” and their water has levels of heavy hydrogen similar to that of Earth’s water, strongly suggesting that these were the source of our water.
So now we know how water came to originate on Earth, these meteorites however, were not rich in salts, that begs the question- How did our oceans gain such high levels of salt?
So, after water came into existence on Earth, the heat on the earth’s surface caused the frozen water to turn into water vapour. Oxygen levels began to increase, forming an atmosphere and this cooled the surface of the earth, eventually forming the crust. Once enough water vapour was collected, the vapour turned into liquid and came down as rain. Runoff from the land and openings in the seafloor contributed to the salinity of the oceans. Rainwater that fell on land was slightly acidic, so it eroded rocks. This released ions that were carried away to streams and rivers that eventually fed into the ocean. Many of the dissolved ions were used by organisms in the ocean and removed from the water. Others were not removed, so their concentrations increased over time.
Another source of salts in the ocean is hydrothermal fluids, which came from vents in the seafloor. Ocean water seeps into cracks in the seafloor and is heated by magma from the Earth’s core, the heat causes a series of chemical reactions. The water tends to lose oxygen, magnesium, and sulphates, and pick up metals such as iron, zinc, and copper from surrounding rocks. The heated water is released through vents in the seafloor, carrying the metals with it.
Fun fact: The oceans initially had extremely high levels of Iron, causing the colour of the oceans to be green instead of blue.
Earlier, I mentioned that the seafloor contains vents which contribute to the ocean’s salinity. These vents are known as hydrothermal vents. Hydrothermal vents are cracks in the ocean floor from which heat escapes from under the crust, they are like geysers or hot springs on the ocean floor. Hydrothermal vents are the result of seawater percolating down through fissures in the ocean crust in the vicinity of spreading centres or subduction zones (places on Earth where two tectonic plates move away or towards one another) so the common places deep hydrothermal vents are found are near the edges of tectonic plates, undersea mountain ranges and seamounts, and mid-ocean ridges. The cold seawater is heated by hot magma and remerges to form the vents. Seawater in hydrothermal vents may reach temperatures of over 700° Fahrenheit but the seawater in the vents does not boil because of the extreme pressure at the depths where the vents are formed.
The deep-sea environment where these vents are formed is completely dark, and photosynthesis; a process by which plants and algae use sunlight to sustain themselves, is impossible. So, bacteria evolved to undergo chemosynthesis; the synthesis of organic compounds by bacteria or other living organisms using energy derived from reactions involving inorganic chemicals, typically in the absence of sunlight, where they draw energy from these gases from the vents to sustain themselves.
What’s interesting is that the last universal common ancestor was traced back to organisms that formed underwater near hypothermal vents. This venerable ancestor was a single-cell, bacterium-like organism known as LUCA, the acronym of the Last Universal Common Ancestor, and is estimated to have lived some four billion years ago, when Earth was a mere 560 million years old.
 |
| LUCA |
All organisms evolved
from Luca that lived when Earth was a celestial baby. After all those billions
of years of change, LUCA's fingerprints are still visible in the genes of
modern organisms.
Citations:
How water came into
existence-
https://www.youtube.com/watch?v=_LpgBvEPozk
Source of the
ocean’s salinity-
https://oceanservice.noaa.gov/facts/whysalty.html
Hydrothermal
vents-
https://oceana.org/marine-life/marine-science-and-ecosystems/deep-hydrothermal-vent
https://oceanservice.noaa.gov/facts/vents.html
https://www.nationalgeographic.org/media/deep-sea-hydrothermal-vents/
Luca –
https://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html
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