Canada has Less Gravity
Earth is a planet that has more gravitational force. Even though being on the surface of the Earth, Canada has less gravity compared with the rest of the Earth’s surface. Do you know the reason behind this? Firstly, What is gravity and how it is created?
“Gravity is proportional to mass”. So when the mass of an area is lower, gravity also reduces. So gravity varies on different parts of the Earth. As the Earth’s shape is not equally scattered. Its equator is bulgy and the poles are flatter. So mass on all the surface of the Earth is not same. And so obviously, gravity differs on the Earth’s surface wherever mass varies.
Although scientists had been working on this for more than 40 years. They tried to figure out the reason why large parts of Canada has less gravity, especially Hudson Bay. Even its surrounding regions have lower gravity than the rest of the world. This phenomenon was first found in 1960 when the Earth’s global gravity fields were being charted.
Finally, scientists have proposed two theories to say how the proportionality of mass and gravity theory works on Hudson Bay area and hence contributes to lower gravity in that area.
Theory 1: Convection occurring in the Earth’s mantle
The mantle is the second layer of the Earth that has molten rocks called “Magma”. This layer exists between 100 to 200 km below the surface of the Earth. Magma is an extremely hot layer and constantly whirling and shifting, rising and falling, to create convection currents. Convection drags the Earth’s continental plates down. This decreases the mass in that area and hence decreases the gravity.
Theory 2: The Laurentide Ice Sheet
The Laurentide Ice sheet has covered much of present-day Canada and the northern United States. This ice sheet is almost 3.2 km thick in most sections In two areas of Hudson Bay, it was 3.7 km thick. It was also very heavy and weighed down the Earth. Over a period of 10,000 years, the Laurentide Ice Sheet melted, finally disappearing 10,000 years ago. It left a deep indentation in the Earth. This theory proposes that the Earth isn’t bouncing back, rather it is rebounding to its normal state very slowly. The rebounding occurs less than half an inch per year. In the meantime, the area around Hudson Bay has less mass because some of the Earth has been pushed to the sides by the ice sheet. And as we know that mass is proportional to gravity. So the gravity decreases along with the mass.
Both the theories found to be true as they are causing some decrease in the gravity around Hudson bay region.
Let’s see the Laurentide Ice Sheet theory. To calculate the impact of the Laurentide Ice Sheet, scientists at the Harvard-Smithsonian Center for Astrophysics used data gathered by the Gravity Recovery and Climate Experiment (GRACE) satellites between April 2002 and April 2006. The GRACE satellites are highly sophisticated machines, orbiting about 500 km above the Earth and 220 km apart. The satellites are capable of measuring distances down to a micron. So they can detect minor gravitational variations. When the lead satellite flies over the Hudson Bay area, the decrease in gravity causes the satellite to move slightly away from the Earth and from its sister satellite. This shift in the distance is detected by the satellites and used to calculate the change in gravity. Any shifts detected can also be used to create maps of gravitational fields.
The GRACE data allowed scientists to create topographical maps approximating what Hudson Bay looked like during the last ice age when it was covered by the Laurentide Ice Sheet. These maps revealed some interesting features about the area, including two bulging areas on the western and eastern sides of Hudson Bay. The ice was much thicker than the rest of the sheet in that area. Gravity is now lower there than in other parts of the gravity-depleted bay.
The GRACE data found another important thing that the ice sheet theory only accounts for 25 to 45% of the gravitational variation around Hudson Bay and the surrounding area. Subtracting the “rebound effect” from the area’s gravitational signal, scientists have determined that the remaining 55 to 75% of the gravitational variation is likely due to convection.
The Hudson Bay area is going to have less gravity for a long time. It’s estimated that the Earth has to rebound more than 650 feet to get back to its original position. And this should take about 5,000 years. But the rebound effect is still visible. Although sea levels are rising around the world. The sea level along Hudson Bay’s coast is dropping as the land continues to recover from the weight of the Laurentide Ice Sheet.
Scientists involved in the Harvard-Smithsonian Center study were amazed. They were able to see how the Earth looked 20,000 years ago. And by isolating the influence of the ice sheet’s rebound effect, they understood how convection affects gravity. They even could know how continents change over time.
Finally, the GRACE satellites have provided scientists with data on many ice sheets and glaciers. The researchers completely examined the reason why parts of Canada has less gravity with the GRACE satellite. Additionally, they examined the climate changes that took place thousands of years ago. They might have gained a better understanding and complete knowledge of how global warming and rising sea levels are affecting our planet. Also, they might have understood the impact that they will have in the upcoming times.
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