(ORDO NEWS) — The authors of the new work believe that this factor may explain why the extinction in the northern hemisphere was more serious than in the southern.
An international group of scientists tried to clarify what season was on Earth at the time of the fall of the Chicxulubu body on it. Based on the fish that died directly from the consequences of this one hundred million megaton impact.
This could aggravate the position of the species of the northern hemisphere in comparison with the species of the southern hemisphere.
The researchers studied deposits in North Dakota, quite far from the impact point of the Chicxulub asteroid. Nevertheless, this zone suffered literally tens of minutes after its fall. A super-powerful explosion (two million “Tsar-bombs”) gave serious earthquakes and tsunamis that go deep into the land.
The value of the formed layer of remains is that there are traces of a meteorite impact in the fossil remains. These are small particles, including glass spherules, formed only during especially powerful atomic and asteroid explosions.
However, in other systems of fish buried in the fossil layer, there are no such traces. In other words, they died instantly, in the first hour after the impact, and this makes it possible to understand for sure that all the remains belong to the season when the asteroid fell.
The authors note that this zone was located at the end of the Mesozoic at 50 degrees north latitude, and therefore had a pronounced seasonality. In particular, in winter it had an average temperature of +4–6 °C.
In summer, the average temperature was 19°C, which is typical in the subtropics and tropics these days. Such fluctuations in temperature also meant the seasonality of the life cycles of local animals.
To understand what season it was at the time of the Chicxulub impact, scientists analyzed the remains of the bones and fins of fish found in the late Mesozoic layer in North Dakota.
It turned out that the isotopes in the outer layers of fish bones indicate clear annual cycles in their development. During warmer seasons, some isotopes accumulated in their bones faster than during colder ones. And the bones of the fish found were in a state corresponding to spring in the northern hemisphere.
It has already been noted in a number of earlier works that in the southern hemisphere the consequences of the extinction of the end of the Mesozoic were somewhat less severe, and the restoration of ecosystems here was faster than in the northern hemisphere.
In light of the new data, this makes sense: ecosystems are more vulnerable in spring than in autumn, when many animals have put on fat to prepare for the cold season. In contrast, in the spring, fat stores are often very low, and the need to breed in many species further complicates the situation.
After the fall of the Chicxulub body, a long asteroid winter set in, during which average temperatures could reach -20°C or less even at low latitudes.
The Mesozoic world was warm (even subtropical forests grew near the South Pole), so such a harsh and long winter was an extremely serious test for it, which most species of large land animals could not endure.
The authors of the work note that all dinosaurs, except birds, as well as pterosaurs, were especially vulnerable in this situation.
The fact is that these groups hatched eggs much longer than birds, since the development of the teeth of the embryo takes a noticeable time. Birds without teeth, and hatching eggs for less time, were not tied to the same places for a long time, and could survive even in such a catastrophe.
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