(Photo: Wikimedia Commons/Gerald Ludwig, U.S. Fish and Wildlife Service)
Gravity rules the Earth, and that's why everything falls. However, an area in Canada seemingly escaped the law of gravity as it reportedly had a region where gravity was missing.
Hudson Bay Gravity Anomaly
Hudson Bay possesses less gravitational force than the rest of the planet. It is important to note that you will not float there, but your weight will be lower than it would be elsewhere in the world.
Scientists have been attempting to determine the cause of the "missing" gravity in huge sections of Canada, especially the Hudson Bay region, for almost 40 years. Put another way, the gravity in the Hudson Bay region and its environs is lower than globally, a phenomenon first noticed in the 1960s while mapping Earth's worldwide gravity fields.
Gravity is fundamentally a function of mass. Therefore, gravity decreases when an area's mass decreases in some way. Different locations on Earth have varying amounts of gravity.
The Earth is a ball, but it bulges at the Equator and becomes flatter at the poles because of rotation. The mass of the Earth is not distributed proportionately, and its location can change throughout time.
Scientists proposed two theories to explain why the gravity in the Hudson Bay region had dropped and how the region's mass had diminished.
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2 Theories About Missing Gravity in Canada
Two theories are attempting to explain the gravity anomaly in Canada. One suggests that it's due to a process known as convection occurring in the Earth's mantle, and the second involves the Laurentide Ice Sheet.
According to the first theory, molten rock, or magma, between 60 and 124 miles (100 and 200 km) below the Earth's surface is known as the mantle. The intense heat and continuous swirling, shifting, rising, and falling of magma produce convection currents, which drag the Earth's continental plates downward, lowering the local mass and gravity.
The second theory relates to the Laurentide Ice Sheet, which encased many northern United States and modern-day Canada. In most places, this ice sheet measured nearly two miles (3.2 km) thick; in two locations in Hudson Bay, it measured 2.3 miles (3.7 km) thick.
Additionally, it was cumbersome and burdened the Earth. The Laurentide Ice Sheet melted over 10,000 years, leading to its complete disappearance 10,000 years ago. It carved a large hole in the Earth.
To understand what transpires, consider what occurs when you lightly press your finger into the surface of a cake or a particularly springy loaf of bread. There's a movement to one side and an indentation. It returns to normal when you take your finger off of it, though.
According to the hypothesis, something similar happened with the Laurentide Ice Sheet; however, instead of the Earth "bouncing" back, it is rebounding very slowly (less than half an inch per year). Meanwhile, because part of the Earth has been pushed to the sides by the ice sheet, the region surrounding Hudson Bay has less mass. And less mass means less gravity.
Data from the Gravity Recovery and Climate Experiment (GRACE) satellites produced topographical maps between April 2002 and April 2006 that roughly depicted Hudson Bay's appearance during the last ice period. The ice sheet theory explains only 25 - 45% of the gravitational variation over Hudson Bay and its environs. Scientists have calculated that between 55 and 75 percent of the gravitational variation in the region is probably caused by convection after deducting the "rebound effect" from the gravitational signal.
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