The life strategy of plants that dominate our forests today may be linked to a massive meteorite that slammed into Earth 66 million years ago, according to a new study.
At the end of the Cretaceous period, a 6.2-mile-wide space rock landed off the Yucatan coast. The impact and the ensuing tsunamis, hurricanes, forest fires and earthquakes are believed to be responsible for one of the worst extinction events our planet has ever seen, including the demise of the dinosaurs. It has also been linked to the extinction of 50 percent of Earth’s plant life.
Now, a paper published in the journal PLOS Biology suggests that the flowering plants that survived this catastrophic event had different survival strategies than those that were wiped out. Slow-growing evergreen plants such as holly and ivy appear to have been more prominent before the meteorite hit, while fast-growing flowering plants that lose their leaves during their lifetimes were more prevalent afterward.
“Before the impact we saw a live-slow-and-safely strategy; then we saw a shift to (a) live-fast, die-young strategy,” said lead author Benjamin Blonder.
To come to this conclusion, Blonder examined 10,000 fossilized plants, mostly from the collection of the Denver Museum of Nature and Science. The fossils spanned a time period of 2.2 million years, from the last 1.4 million years of the Cretaceous (pre-meteorite hit) to the first 800,000 years of the Paleocene (post-meteorite hit). They all came from southern North Dakota in an area called the Hell Creek Formation.
Blonder was looking for two ways to characterize the fossilized leaves. The first was leaf mass per area, which tells him whether the leaf was chunky and “expensive” for the plant to make, or if it was flimsy and “cheap.” He also looked at the density of the leaves’ vein networks. The more veins a plant has, the more quickly it can acquire carbon for photosynthesis.
The results were clear: Before the impact, plants were more likely to have high leaf mass per area and low vein density, after the impact they had lower leaf mass per area and higher vein density.
The researchers hypothesize that in the chaotic aftermath of the Chicxulub impact, as the meteorite strike is known, the plants with the flimsy leaves were more adept at surviving changing climate conditions than those that had invested a lot of energy into each leaf.
Blonder noted that neither strategy is empirically better than the other.
“Oftentimes when people think of evolution they imagine that life is moving toward some ideal. That is not the case,” he said. “Plants like holly and ivy are still around, still growing and reproducing and in no danger of going extinct.”
The study looks only at flowering plants—trees are not included. Also, since all the plants came from the same area, it is unclear whether the findings would hold true in other parts of the world.
“That is one of the big questions,” Blonder said.
He thinks that the area the fossils came from is broad enough that it could be representative of North America, but beyond that he can’t say.
“The problem is, data sets of this quality are hard to come by,” he said. “Looking into the Earth’s past is a difficult business.”
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