Event name: Andrew H. Knoll - Through Space and Time
Event time and place: Edward St. John Teaching and Learning Center, University of Maryland on April 4th, 2024
I attended Andrew H. Knoll's presentation "Through Space and Time" on April 4th, 2024 in the Edward St. John Learning and Teaching Center. The presentation focused on the fossil record of life and environment over time. The oldest fossil record of animals is only 575 million years old and animals make up a much smaller portion of the estimated global biomass compared to plants. The three major branches of the last universal common ancestor are bacteria, archaea, and eukaryote, and animals only make up a small portion of eukaryotes. Some earlier records of life and environment include carbonates, microbes, and stromatolites. Ancient oceans were covered with microbial communities. Chemical clues from biomarker molecules exist in older rocks. For example in Northern Siberia, these biomarkers and isotopic signatures show signs of microbial reefs. Early life existed before oxygenation which occurred 2.2 to 2.4 billion years ago. Signs of oxygenation come from banded iron formations, sulfur isotopes, and detrital uraninite and pyrite. Oxygenic photosynthesis from cyanobacteria contributed to oxygenation. At the beginning of the Paleozoic era, oxygen reached modern levels. During the Cambrian Explosion, there was an increase in bilateral body plans. The emergence of macroscopic animals coincided with the increase in oxygen. While not a lot of oxygen is needed for sponges to survive, animals require a much higher level of oxygen. Also, an increase in continental runoff leads to an increase in phosphorus, increasing photosynthesis. This increase in nutrients and oxygen leads to animal diversification.
I believe that the main points of the presentation were convincing. Throughout the presentation, Dr. Knoll cited many studies that supported his conclusions, some of which he himself or his colleagues conducted. Additionally, he showed many of the sites of rock formations, some of which he had visited himself, including Shark Bay, Bahama Banks, and Mistaken Point, Newfoundland. The rock formations at these sites contained microbes which revealed information about life and environment during the time periods they formed. For example, carbonates were deposited on the Bahama Banks and stromatolites can be found in Shark Bay. At Mistaken Point, Newfoundland, Ediacaran fossils from more complex organisms from about 565 million years ago can be found. In Northern Siberia, both molecular biomarkers and isotopic signatures showed the existence of microbial reefs in the rock formations. The support of Dr. Knoll's arguments with data from specific sites made his points very convincing.
My prior knowledge on this topic aligns with the claims made during this presentation. For example, since animals are very new to Earth compared to bacteria and plants, it makes sense that they make up a smaller portion of Earth's total biomass. Additionally, since animals are much more complex than bacteria and microorganisms, they appear much later in the fossil record. My background knowledge about plant growth supports the argument that an increase in phosphorus increases photosynthesis, which in turn increases oxygen levels. Phosphorus is one of the main nutrients that plants need from soil as it is needed for cell division, photosynthesis, and healthy plant growth. While an increase in nutrients and oxygen most likely contributed to the Cambrian Explosion and helped support more complex life forms, there were likely many other factors that contributed to this. Dr. Knoll discussed other factors such as the rise of carnivory, which he believed was a driver of ecological diversity. By discussing multiple factors Dr. Knoll crafted a more holistic explanation of how the Cambrian Explosion occurred.
At times, especially during the question and answer segment, Dr. Knoll considered many different possible viewpoints. For example, when asked about the origins of life, he discussed the two primary ideas, either in lakes or in hypothermal vents in the oceans. By considering multiple viewpoints and expressing that there was a need for more research in these areas, he avoided logical fallacies. This approach helped to strengthen his argument and create a more open scientific discussion.