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What happened during the Cretaceous-Paleogene extinction?
The Cretaceous-Paleogene extinction began with an immense asteroid impact in Mexico. It was one of six extinction events that took place on Earth. It’s often abbreviated as the K-T or K-Pg extinction. 65 million years ago, this massive event wiped out some of the Earth’s most dominant animals, like dinosaurs and marine reptiles. The asteroid created a six-mile-wide crater, and the immediate heat generated by the impact sparked wildfires across the world. Dust and debris that shot up from the crater was everywhere. Soot gathered from the wildfires. These particles blocked sunlight and plunged the Earth into a sudden dark winter. The oceans turned acidic and impacted marine life. It was like an enormous insulation blanket was laid over the atmosphere, cooling the Earth and changing the climate drastically from what it used to be.
It’s no surprise that so much of life found it difficult to survive after the impact. Sudden climate change is having similar impacts now, 66 million years later. It’s causing massive extinctions, wiping out entire lineages.
How did flowering plants evolve?
From towering maples and oaks to tiny roses, tulips and lilies, flowering plants exist in all shapes and sizes. They occupy every corner of the world, from North America to Antarctica. Flowering plants are also known as angiosperms. Angiosperms are diverse and widespread, representing almost 78% of all land plants. Land plants first popped up around 475 million years ago, well after algae and fungi. It took a long time for plants to get used to land and begin to flower – around 300 years. Angiosperms finally began to evolve around 130 million years ago. 130 million years might not sound like a short time, but on an evolutionary scale it’s the blink of an eye. They existed for around 70 million years prior to the K-T extinction.
After angiosperms appear in the fossil record, they suddenly diversify, forming hundreds of species. Organisms are constantly in competition with each other for resources. Occasionally, life comes up with a key innovation. A key innovation allows one kind of organism to access resources that nobody else has gotten to. Flowers and seeds are a key innovation which allowed angiosperms to beat out all other land plants.
Pollination is central to the success of flowering plants. Pollen from one flower enters another. This makes the offspring plants more diverse. The fruits that form after pollination protect the seeds. Animals that eat the fruits take the seed far away, allowing the plants to colonize new areas. All of these processes didn’t exist before flowering plants!
Interestingly, flowering plants and insects seemed to have evolved together. Since flowers benefit insects, and insects benefit flowers, both of them benefitted from this association!
How do we know flowering plants survived mass extinction?
Today, we find out how animals are related to each other using their visual features, as well as genetic information. We can then draw linkages between different lineages – it’s like a family tree, but for species. This process is known as phylogeny. When trying to track extinctions, it’s very important to see if there are certain groups that are going extinct more than others. In the case of angiosperms, we found out that they were going extinct much less than other lineages.
Fossils are our window into ages past. Although advances are being made in trying to recover genetic data from more recent bone fossils, 65 million years is too far back for DNA to survive. Researchers have to rely on the features they can see through fossils alone. The fossil record is also imperfect. We can only examine what we’ve found, and many fossils remain buried deep in the ground. Certain animals, like those with bony skeletons and hard shells also preserve better. Plant fossils are particularly rare.
Despite all of these challenges, researchers have managed to uncover a spectacular number of plant fossils. Comparing the features, they grouped together similar looking plants into lineages. By examining the number of lineages which look similar to the flowering plants we see today, researchers estimated how many flowering plant groups went extinct. Although many individual species went extinct, particularly those close to the asteroid impact site, a vast number of lineages persisted.
Scientists are unsure why flowering plants in particular were able to survive the mass extinction when other species weren’t able to. In general, large organisms seem to go extinct at higher rates than smaller organisms. Large life forms need more resources, and often struggle in times of scarcity. Smaller flowering plants might have weathered the extinction event better.
Angiosperms also have a curious ability to double their genetic material. Many flowering plants seem to have doubled their genetic material around the same time as the K-T extinction, but it’s not clear whether it happened before or after the event. Research is ongoing as to why this doubling might have helped them survive.
It’s incredible to imagine that our buttercups and sunflowers are survivors. Their ancestors withstood one of the worst mass extinctions on planet Earth, and continued to flourish. The next time a flower in your garden blooms in the midday sun, remember that its ancestor bloomed under a sky of asteroid debris – and survived!
Glossary
Key innovation: A new trait that allows the success of a particular group
Phylogeny: A family tree of species and lineages
Pollination: The movement of pollen from one flower to another
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Yamini Srikanth: Author Yamini's (he/they) interests lie in environmental education, science communication and trying to build a better world. When not languishing in front of his laptop, they can be found outside, poking at any insect, bird or plant. They love making science accessible, especially to those who aren't encouraged to pursue it. Yamini hopes that the young women who read Smore love learning from their articles and get just a little bit more excited about science! View all posts
