I was on a hike and read a plaque that said this area used to be completely covered by water. My question is, where did all that water go? Just absorbed into the ground? Evaporated?
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Most of what is currently downtown Boston was under water. They literally filled the water with sand and dirt and created what we now know as Boston. Originally it was a small piece of land connected to the rest of the city by a narrow neck of land.
Most of what is currently downtown Boston was under water. They literally filled the water with sand and dirt and created what we now know as Boston. Originally it was a small piece of land connected to the rest of the city by a narrow neck of land.
It depends.
If water evaporates and falls as rain, it just runs into a river and back into the sea. But if it falls as snow and the snow doesn’t melt, that lowers sea level. The Antarctic ice sheet formed that way about 40 million years ago and dropped sea level about 100 metres.
Another thing ice does is pushes the crust down, and when the ice melts the land slowly rebounds upwards. Much of Finland was covered in ice during the last glacial period, then flooded after the ice sheets melted, but is now dry land.
Over longer time periods, plate tectonics affects the depth of the oceans. Young seafloor is higher – as it gets older it cools and sinks down into the mantle. If the oceans are less deep then the water ends up flooding the continents. This process is part of what made the Western Interior Seaway across much of what is now the USA.
Estimates of past sea level have it about 400 metres above the present day at the highest. To get marine rocks *really* high up required plate tectonics to drive land upwards. When continents collide the rocks crumple forming mountains and plateaus. There can also be gentler upward and downward bending further away from the main collision or through other processes. This helped create the western seaway I mentioned – the sea rose up but the land went down too.
As far as I know there’s no significant change from water entering or leaving the deep earth over the past few hundred million years.
It depends.
If water evaporates and falls as rain, it just runs into a river and back into the sea. But if it falls as snow and the snow doesn’t melt, that lowers sea level. The Antarctic ice sheet formed that way about 40 million years ago and dropped sea level about 100 metres.
Another thing ice does is pushes the crust down, and when the ice melts the land slowly rebounds upwards. Much of Finland was covered in ice during the last glacial period, then flooded after the ice sheets melted, but is now dry land.
Over longer time periods, plate tectonics affects the depth of the oceans. Young seafloor is higher – as it gets older it cools and sinks down into the mantle. If the oceans are less deep then the water ends up flooding the continents. This process is part of what made the Western Interior Seaway across much of what is now the USA.
Estimates of past sea level have it about 400 metres above the present day at the highest. To get marine rocks *really* high up required plate tectonics to drive land upwards. When continents collide the rocks crumple forming mountains and plateaus. There can also be gentler upward and downward bending further away from the main collision or through other processes. This helped create the western seaway I mentioned – the sea rose up but the land went down too.
As far as I know there’s no significant change from water entering or leaving the deep earth over the past few hundred million years.
Picture a tub full of water with paper plates floating on top.
The plates are floating but also really crowded together. Basically the water in the tub has plates covering it edge to edge.
The water isn’t stagnant. It moves a little, which causes some of the plates drift away from each other, or overlap, or brush past each other.
When the plates overlap, one is pushed up while one is pushed down. This can cause mountains to form from what was a flat or underwater area previously. If the plates move away from each other, a gap is formed that can be filled with water.
In this example the water is like the earth’s molten core (liquid rock) on which the tectonic plates that make up the continents are floating. They move around and as they do they either get pushed up, pushed down, pushed away, or slid past. Because it’s solid rock floating on top of liquid rock these changes take a long time, but eventually create drastic changes on the surface. Tectonic plate movement is how both mountains and oceans are formed.
Picture a tub full of water with paper plates floating on top.
The plates are floating but also really crowded together. Basically the water in the tub has plates covering it edge to edge.
The water isn’t stagnant. It moves a little, which causes some of the plates drift away from each other, or overlap, or brush past each other.
When the plates overlap, one is pushed up while one is pushed down. This can cause mountains to form from what was a flat or underwater area previously. If the plates move away from each other, a gap is formed that can be filled with water.
In this example the water is like the earth’s molten core (liquid rock) on which the tectonic plates that make up the continents are floating. They move around and as they do they either get pushed up, pushed down, pushed away, or slid past. Because it’s solid rock floating on top of liquid rock these changes take a long time, but eventually create drastic changes on the surface. Tectonic plate movement is how both mountains and oceans are formed.
Its very possible that the earth used to be covered in water. Recent research suggestes that ancient earth (3 billion years ago) was a water world, covered in water with no continents. In other words, it was formless and void, and darkness was over the face of the deep, haha.
https://news.harvard.edu/gazette/story/2021/04/harvard-scientists-determine-early-earth-may-have-been-a-water-world/#:~:text=Calculations%20show%20that%20Earth’s%20oceans,been%20completely%20covered%20in%20water.
Its very possible that the earth used to be covered in water. Recent research suggestes that ancient earth (3 billion years ago) was a water world, covered in water with no continents. In other words, it was formless and void, and darkness was over the face of the deep, haha.
https://news.harvard.edu/gazette/story/2021/04/harvard-scientists-determine-early-earth-may-have-been-a-water-world/#:~:text=Calculations%20show%20that%20Earth’s%20oceans,been%20completely%20covered%20in%20water.
Sea levels have changed over time (e.g. due to melting and freezing of the ice caps) but in that particular case it’s more likely that the spot you were on used to be at a much lower elevation, and geologic activity has pushed it up above sea level.
Fun fact: the very top of Mount Everest is made of grey limestone, which only forms in underwater environments, and contains fossils of marine organisms. So around 450 million years ago, it was underwater too.
Sea levels have changed over time (e.g. due to melting and freezing of the ice caps) but in that particular case it’s more likely that the spot you were on used to be at a much lower elevation, and geologic activity has pushed it up above sea level.
Fun fact: the very top of Mount Everest is made of grey limestone, which only forms in underwater environments, and contains fossils of marine organisms. So around 450 million years ago, it was underwater too.
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