4 ms·

When I was a kid I remember older grade-school science books telling about ice ages. According to the books, there had been 4 (or maybe 5) ice ages in the past

When I was a kid I remember older grade-school science books telling about ice ages. According to the books, there had been 4 (or maybe 5) ice ages in the past, the last one was N years ago (maybe 20,000 or something), and there weren't going to be any more. And I was like "how can they know there won't be any more?". Do I mis-remember what those books said? Did geologists actually believe something like that? I guess those books must have been from the 1970s or earlier, but still.

saiya-jin 5y ago
I imagine there have been tons of ice ages similar to last one which ended only... 10k years ago? Where I come from, the mountains were cut pretty deep even from this last one which was pretty insignificant on long-term scale. And of course all previous ones left their marks, but the deep scratches were mostly removed by later ones. Maybe its about defining what a news-worthy ice age means. It for sure shouldn't be just snowball Earth type when most of the planet apart from a bit of equatorial places froze solid white.
cbkeller 5y ago
I'm not aware of any time when that was a mainstream belief, but there might be a gap in my history-of-science knowledge. In any case, while we're currently in an "interglacial" period with respect to the Pleistocene glacial cycles, we're actually still in an "icehouse" period by the big-picture definition, since there are continental icesheets on Greenland and Antarctica. By contrast, a lot of the rest of the Phanerozoic has been characterized by "hothouse" climates, where there are no major continental icesheets anywhere on Earth. It's possible that anthropogenic CO2 emissions will prevent us from going back into a colder "glacial" period when we otherwise next would have ~80 kyr from now, but geologic time is long and there is a lot of it still in front of us.

saiya-jin 5y ago

I imagine there have been tons of ice ages similar to last one which ended only... 10k years ago? Where I come from, the mountains were cut pretty deep even from this last one which was pretty insignificant on long-term scale. And of course all previous ones left their marks, but the deep scratches were mostly removed by later ones. Maybe its about defining what a news-worthy ice age means. It for sure shouldn't be just snowball Earth type when most of the planet apart from a bit of equatorial places froze solid white.

cbkeller 5y ago

I'm not aware of any time when that was a mainstream belief, but there might be a gap in my history-of-science knowledge. In any case, while we're currently in an "interglacial" period with respect to the Pleistocene glacial cycles, we're actually still in an "icehouse" period by the big-picture definition, since there are continental icesheets on Greenland and Antarctica. By contrast, a lot of the rest of the Phanerozoic has been characterized by "hothouse" climates, where there are no major continental icesheets anywhere on Earth. It's possible that anthropogenic CO2 emissions will prevent us from going back into a colder "glacial" period when we otherwise next would have ~80 kyr from now, but geologic time is long and there is a lot of it still in front of us.