LC6C. Stay Current—How and When Did Complex Life Begin?

Understanding Evolution – a one-stop source for information on evolution.2019-11-14. Alien genes from bacteria helped plants conquer the land. By Elizabeth Pennisi, Science Magazine. 

2024-03-07. Peering into the past to identify the species most at risk from climate change. [https://www.science.org/doi/10.1126/science.adj5763] By Erin Saupe, Cooper Malanoski, et al, Science. Excerpt: A polar bear floating on a tiny piece of sea ice has become the iconic image of the extinction risks of climate change. But not all threats to species from our warming planet are so easy to see. That’s why paleobiologist Erin Saupe, Ph.D. student Cooper Malanoski, and their colleagues turned to the fossil record. By understanding which species fell victim to climactic fluctuations in the past, they aimed to get a better sense of which organisms might be most vulnerable now. “Despite the threat that climate change poses to biodiversity, we do not yet fully understand how it causes animals to go extinct,” Saupe and Malanoski explain in an article for The Conversation. So, the team examined data from nearly 300,000 marine invertebrate fossils from the last 485 million years, using statistics to examine how traits of the animals and their environment link to their likelihood of extinction. “Alarmingly, our research has, for the first time, identified climate change as a significant predictor of extinction,” the pair write. Species that experienced local climate changes of 7°C or greater were more likely to perish, regardless of any specific traits, they report in the most recent issue of Science. [Climate change is an important predictor of extinction risk on macroevolutionary timescales] …The best predictor of extinction was a small geographic range, but smaller bodies and a narrow temperature tolerance added to a species’ odds of dying out.

2016-01-11. Ancient Start of Animal Evolution Wasn’t Delayed by Low Oxygen. By Cody Sullivan, Earth & Space Science News (EoS; AGU). Excerpt: New research finds that Earth had sufficient oxygen 1.4 billion years ago for animals to evolve. Therefore, low oxygen levels probably didn’t hold back evolution, as scientists have long thought….  https://eos.org/articles/ancient-start-of-animal-evolution-wasnt-delayed-by-low-oxygen

2010 July 26. Translating Stories of Life Forms Etched in Stone. By Sean B. Carroll, The New York Times. Excerpt: …The difficulty posed by the Cambrian Explosion was that in Darwin’s day (and for many years after), no fossils were known in the enormous, older rock formations below those of the Cambrian. This was an extremely unsettling fact for his theory of evolution because complex animals should have been preceded in the fossil record by simpler forms… but we now have fossil records from the time immediately preceding the Cambrian. The rocks reveal a world whose oceans were teeming with a variety of life forms, including primitive animals, which is certainly good news for Darwin.
…This once-worrisome gap in the fossil record is a period of intense interest to geologists as well as paleontologists. The former have even given it its own division in the geological timescale. The Ediacaran Period, from 635 to 542 million years ago, is the first new geological period to be named in more than a century. Moreover, geologists have developed some intriguing theories about how dramatic changes in the Earth’s climate and chemistry during the Ediacaran may have allowed for the evolution of animals
…But finding these fossils has posed many new mysteries. Many of the creatures are so unlike modern forms that deciphering what they are and how they lived continues to challenge paleontologists. Prof. Andrew Knoll of Harvard University has likened the Ediacaran forms to a paleontological “Rorschach” test because different scientists often interpret the same fossil very differently.
…The kinds of animals that paleontologists have been especially eager to identify in the Ediacaran are those with bilateral body symmetry, the feature characteristic of the majority of modern animal groups, including ourselves.
…Recent chemical analyses of Ediacaran sediments reveal that the deep ocean lacked oxygen before and during that ice age, then became much richer in oxygen and stayed that way after the glaciers melted. That sharp rise in oxygen may have been the catalyst to the evolution of animals, including our ancestors.

2008 October 17. Evolution Primers. National Center for Science Education – articles on evolution.