Question

1.How did plants contribute to the first mass extinction event? Please answer in detail.

2.Take a look at the Revive and Restore project. What are two animals they are attempting to bring back? How? Will these be identical to the original? Is this project worth doing?

Answer 1

1. An extinction event ( mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the rate of speciation.

"In the plant kingdom, mass extinction events can be seen as opportunities for turnover leading to renewed biodiversity," Some important plant groups, such as the "gymnosperms " (including pines, spruce and firs) lost a great deal of their diversity through extinction. On the other hand, flowering plants (angiosperms) did not suffer from increased extinction, and shortly after the impact they underwent a new rapid increase in their diversity. These evolutionary dynamics contributed to make flowering plants dominate today's global diversity above all other plant groups.

Fossils of microscopic spores indicate that simple plants perhaps similar to mosses and liverworts of today first arrived on land roughly 470 million years ago. This happened relatively recently compared to another Earth shaping event perpetrated by tiny microorganisms that share plants ability to photosynthesize, or use sunlight to produce sugar. About 2 billion years earlier, cyanobacteria, also called blue green algae, are believed to have begun pumping oxygen into our atmosphere as a by-product of photosynthesis.

At roughly this time, perhaps a little later, the planet cooled, glaciers spread and sea levels dropped. The result was the end-Ordovician mass extinction, which decimated the oceans, where life was largely confined at the time. Before the extinction, the atmosphere had many times the level of carbon dioxide, an important greenhouse gas, we see today. But something caused the carbon dioxide and subsequently, temperatures  to drop.  Plants enhance a process called silicate weathering, which sucks carbon out of the atmosphere and ultimately tucks it away at the bottom of the oceans.

• Caron dioxide in the atmosphere forms carbonic acid. It falls as acid rain, reacting with rocks, which contain silicates, to form bicarbonate. The bicarbonate eventually washes into the ocean and where it forms limestone.
• So, it's almost like a pump that pumps carbon dioxide into the ocean floor," said Liam Dolan, a study researcher and a professor of botany at Oxford University in the United Kingdom. "The ocean floor is where it's sequestered."

Plants help in multiple ways. To get the nutrients they need, plans secrete acids that dissolve rocks, releasing the needed minerals. Later, when roots evolved, plants began physically breaking up the rocks.

A theory called the "Devonian plant hypothesis" suggests that more complex plants, called vascular plants that arrived on the scene much later, contributed to the Devonian mass extinction by the same cooling mechanism.  Dolan and his colleagues suspected that the earlier pioneers had a similar impact. He and colleagues, including Timothy Lenton of the University of Exeter, tested how a modern moss, Physcomitrella patens, affected the release of elements from two types of rock: granite and the softer andesite. They found that the moss enhanced the weathering comparable to vascular plants.

Using a climate model, they showed that, if plants like the moss inhabited 15 percent of the currently vegetated land between 475 million and 460 million years ago, atmospheric carbon dioxide would drop enough to cause global cooling and trigger the spread of glaciers.The land plants may also have contributed to the "extinction" by fertilizing the oceans with phosphorus they released from rocks, Dolan said. This extra phosphorus would have caused the waters to lose oxygen as occurs in modern dead zones, such as in the Gulf of Mexico.

"Thus, the evolution of the first land plants could have indirectly contributed to killing of many of their compatriots in the ocean".

2. "Woolly Mammoth" and a hairy, close relative of the elephant that lived in the Arctic, and the " passenger pigeon", a small, gray bird with a pinkish red breast once extremely common in North America.

There are three main approaches to de-extinction species.

• The first, called "backbreeding", involves finding living species that have traits similar to the extinct species. Selective breeding of these animals is done to make a version that more closely resembles the extinct animal a process already underway for some extinct species like aurochs. This isn’t really a true de-extinction, but it might still let us fill in missing ecological functions. In the case of mammoths, scientists have  tried to mate Asian elephants with more body hair than usual.

• A second option is cloning. Scientists would take a preserved cell from a recently extinct animal (ideally before the last of its kind died) and extract the nucleus. They would then swap this nucleus into an egg cell from the animal’s closest living relative and implant the egg into a surrogate host. The infant lived only 7 minutes however, because of genetic problems with its lungs.) Cloning may eventually give us basically identical genetic copies of extinct species, but we’ll be restricted to animals that went extinct more recently and have well-preserved cells with intact nuclei. The mammoth and the passenger pigeon may never be cloned.

• The lastest option is genetic engineering. In this method , researchers would line up the genome of an extinct animal with that of its closest living relative. They would then use CRISPR and other gene-editing tools to swap relevant genes from the extinct animal into the living species and implant the hybrid genome into a surrogate (or grow it in an artificial womb). This approach doesn’t produce genetically identical copies of extinct animals, but rather modern versions of an animal engineered to look and behave like its extinct relatives. This is the technology being used by the mammoth and passenger pigeon groups.

How identical are they?

“If you're willing to accept something that is an elephant that has a few mammoth genes inserted into its genome and therefore is able to make some proteins that mammoths might, we're probably closer to that,”

In the case of passenger pigeons project , the scientists resurrect the bird using its closest living relative, the band-tailed pigeon, but how many genes need to be swapped to constitute success is somewhat arbitrary. “The two genomes are 97% the same. That 3% has built up over many millions of years and the majority of it is noise,” he says. “So the actual differences are much likely a smaller portion probably within the realm of several thousand mutations.   Genetically coaxing to behave like their extinct relatives might restore the ecosystem’s lost function”. Even if researchers can pinpoint and transfer those key mutations (a daunting task), DNA is only half the battle. From there it’s a matter of getting the hybrid cell to grow in a surrogate, hoping all the genes work harmoniously together, bringing the hybrid to term, and hoping it acts like the extinct species even though it was raised by a modern relative.  

It’s a monumental task, but scientists says that if the team can secure enough funding, “there’s no reason that we can’t have the first generations of passenger pigeons by something like 2022 to 2025. Everyone running these projects would very much like to be in 10-year time frames.

Today, successional habitats are rare and declining throughout eastern North America, leading to declines in dozens of plant and animal species. Human interventions designed to produce successional habitats are costly and infeasible to scale up to meet conservation needs . Restoring passenger pigeons offers a more effective solution. Its somewhat worthy process.