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, 7 (1), 14855

Site of Asteroid Impact Changed the History of Life on Earth: The Low Probability of Mass Extinction

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Site of Asteroid Impact Changed the History of Life on Earth: The Low Probability of Mass Extinction

Kunio Kaiho et al. Sci Rep.

Abstract

Sixty-six million years ago, an asteroid approximately 9 km in diameter hit the hydrocarbon- and sulfur-rich sedimentary rocks in what is now Mexico. Recent studies have shown that this impact at the Yucatan Peninsula heated the hydrocarbon and sulfur in these rocks, forming stratospheric soot and sulfate aerosols and causing extreme global cooling and drought. These events triggered a mass extinction, including dinosaurs, and led to the subsequent macroevolution of mammals. The amount of hydrocarbon and sulfur in rocks varies widely, depending on location, which suggests that cooling and extinction levels were dependent on impact site. Here we show that the probability of significant global cooling, mass extinction, and the subsequent appearance of mammals was quite low after an asteroid impact on the Earth's surface. This significant event could have occurred if the asteroid hit the hydrocarbon-rich areas occupying approximately 13% of the Earth's surface. The site of asteroid impact, therefore, changed the history of life on Earth.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Climate changes caused by black carbon (BC) injection from ejected Chicxulub rocks. (a) Changes in the global averages of BC amounts in the atmosphere, (b) downward shortwave (SW) radiation at the surface, (c) surface air temperature, (d) surface air temperature on land, and (e) precipitation on land for the 20-Tg (orange), 200-Tg (green), 500-Tg (blue), 1500-Tg (black), and 2600-Tg (red) BC scenarios calculated by the climate model. Monthly anomalies from the control experiment (no ejection case) are indicated on the left axis by filled circles (ae), and ratios relative to the control experiment are indicated for shortwave radiation and precipitation on the right axis by open squares (b,e). The 30-year global averages of the amount of BC, downward shortwave radiation at the surface, surface air temperature, surface air temperature on land, and precipitation on land in the control experiment were 41 Gg, 200 W m−2, 287 K, 281 K, and 2.2 mm day−1, respectively.
Figure 2
Figure 2
Seawater temperature changes caused by black carbon (BC) injection from ejected Chicxulub rocks. (ae) Changes in the global averages of seawater temperature at water depths of 2 m, 50 m, 100 m, 200 m, 400 m, and 600 m for the 20-Tg (a), 200-Tg (b), 500-Tg (c), 1500-Tg (d), and 2600-Tg (e) BC scenarios calculated by the climate model. Monthly anomalies from the control experiment (no ejection scenario) are shown. The 30-year global averages of seawater temperature at water depths of 2 m, 50 m, 100 m, 200 m, 400 m, and 600 m in the control experiment were 293, 292, 290, 287, 283, and 280 K, respectively. The regions where seawater temperatures were below 0 °C at a 2-m water depth in the control experiment were excluded for the estimation of the anomalies and 30-year averages, to exclude the sea ice area.
Figure 3
Figure 3
Comparison of climate changes caused by black carbon (BC) injection from low-latitude Chicxulub and high-latitude Popigai rocks for the 200-Tg BC cases. (a) Changes in the global averages of the amount of BC in the atmosphere, (b) downward shortwave (SW) radiation at the surface, (c) surface air temperature, and (d) surface air temperature on land for the low-latitude Chicxulub 200-Tg (green) and the high-latitude Popigai 200-Tg (magenta) BC scenarios calculated by the climate model. Monthly anomalies from the control experiment (no ejection case) are indicated on the left axis by filled circles (ad), and the ratios relative to the control experiment are indicated for shortwave radiation on the right axis by open squares (b). The 30-year global averages of the amount of BC, downward shortwave radiation at the surface, surface air temperature, and surface air temperature on land in the control experiment were 41 Gg, 200 W m−2, 287 K, and 281 K, respectively.
Figure 4
Figure 4
Global map showing the amount of organic matter in sedimentary rocks ejected if the Chicxulub asteroid hit various locations at the end of the Cretaceous. Shaded areas denote the following burned organic carbon weights in each area burned by the asteroid impact: white: <22,000 Tg; olive: 22,000–89,000 Tg; orange: 89,000–220,000 Tg; and magenta: 220,000–890,000 Tg. These areas correspond to 0–4 °C, 4–8 °C, 8–11 °C, and ≥11 °C cooling (global mean surface air temperature anomalies) and 0–6 °C, 6–13 °C, 13–17 °C, and ≥17 °C cooling on land by soot only, respectively, when the asteroid hit each area (Table 3). Mass extinction could have been caused by 8–11 °C or more cooling when the asteroid hit an orange or magenta area, which occupied approximately 13% of the Earth’s surface. The map is based on Courtillot et al.; thin lines indicate continental crust shelf edges.
Figure 5
Figure 5
Relationships between the maximum global mean surface air temperature anomaly and globally distributed amounts of soot from asteroid impacts (black) and the maximum possible sulfate from volcanic eruptions (gray) injected into the stratosphere. The stratospheric soot amount and maximum temperature anomaly (left axis) are taken from Fig. 1a,c. The maximum temperature anomaly on land (right axis) is shown only for the stratospheric soot and is taken from Fig. 1a,d. The K curve was used for estimating the temperature anomalies for the amount of soot (Table 3). Relationships for sulfate and maximum temperature anomaly (left axis) are taken from published data calculated by various global models in volcanic eruption studies and are classified into three categories. The first category is taken from Robock et al. (open circles, marked by R). The second category is taken from Timmreck et al.,, Segschneider et al., and Laakso et al. (filled squares, marked as T, Se, L). Schmidt et al. (open squares, marked as Sc) belongs to this category, but this case gives 10 years of continuous injection of sulfur into the upper troposphere instead of a short-term injection to the stratosphere. The third category is taken from Robock et al., Jones et al., and Harris and Highwood (filled circles, marked as R, J, H). The HR, curve (the first and third categories) and the LTS curve (the second category) were used to estimate the temperature anomalies for the sulfate amounts in the upper and lower cases, respectively (Supplemental Table 1). See the text for details. Amounts of stratospheric soot and sulfate ejected by the Chicxulub impact and sulfate by volcanic eruptions,,, are also shown (Tables 1 and 2).
Figure 6
Figure 6
Phanerozoic faunal changes with approximately 13% probability following the Chicxulub asteroid impact. Changes in fauna are based on extinction rates. Changes through the K–Pg boundary mass extinction are enhanced by a change in the main terrestrial fauna from dinosaurs to mammals.

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