Al Gore predicts the North Pole will be "ice free" in the summer "within 5 to 7 years" 2009 (17 years ago)
Roman concrete was remarkable because it could last for thousands of years, even underwater. Its mixture of lime, volcanic ash, and water allowed it to develop cracks that didnโt weaken it. When water entered a crack, it reacted with the lime to form calcium carbonate, which gradually filled the crack and bonded the concrete back together, essentially giving it a natural self-healing ability.
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