Fish hobbyist, Yvonne Maschke, in front of her aquarium of fishes that she is rehoming over Kijiji. Courtesy of Yvonne Maschke. Yvonne Maschke, a fish hobbyist from Oshawa, has hundreds of Oranda fancy goldfish swimming in tubs in her basement. In the past five years, she has rehomed hundreds of fish all through Kijiji. After putting an advertisement up on Kijiji, it typically takes a few weeks for interested customers to respond and for the fish to be given to its new home. The number of fish given to a customer varies from one to about a hundred, depending on the customer. Doing a quick search or putting up ads on different services lets you see which sites allow you to rehome fish. Rehoming your goldfish is an option you should take before ever considering releasing it into the water, says Brook Schryer, the Aquatic Program Specialist for the Invasive Species Awareness Program in Ontario. He also suggests rehoming it on Kijiji, donating it to a school group or returning it to the store where it was purchased.
Most people envision radiometric dating by analogy to sand grains in an hourglass: the grains fall at a known rate, so that the ratio of grains between top and bottom is always proportional to the time elapsed. In principle, the potassium-argon K-Ar decay system is no different. Of the naturally occurring isotopes of potassium, 40K is radioactive and decays into 40Ar at a precisely known rate, so that the ratio of 40K to 40Ar in minerals is always proportional to the time elapsed since the mineral formed [ Note: 40K is a potassium atom with an atomic mass of 40 units; 40Ar is an argon atom with an atomic mass of 40 units]. In theory, therefore, we can estimate the age of the mineral simply by measuring the relative abundances of each isotope. Over the past 60 years, potassium-argon dating has been extremely successful, particularly in dating the ocean floor and volcanic eruptions. K-Ar ages increase away from spreading ridges, just as we might expect, and recent volcanic eruptions yield very young dates, while older volcanic rocks yield very old dates. Though we know that K-Ar dating works and is generally quite accurate, however, the method does have several limitations. First of all, the dating technique assumes that upon cooling, potassium-bearing minerals contain a very tiny amount of argon an amount equal to that in the atmosphere. While this assumption holds true in the vast majority of cases, excess argon can occasionally be trapped in the mineral when it crystallizes, causing the K-Ar model age to be a few hundred thousand to a few million years older than the actual cooling age. Secondly , K-Ar dating assumes that very little or no argon or potassium was lost from the mineral since it formed.