Earth.Parts #25 Kerogen & dead-carbon cycling over timescales of thousands to millions of years
Over timescales of centuries to millions of years the retention of carbon (C) as CO2 in the atmosphere is strongly moderated by the burial of organic carbon in sedimentary rocks and the rate of rock weathering at Earth's surface.
Dead plant remains can become buried on land in peat bogs or carried by rivers to the ocean. Dead plankton fall into the ocean depths. Only a tiny amount of dead organic C per year becomes buried in sediments that later are compressed into rock. A similar tiny amount of natural weathering of rocks at Earth's surface, on an annual basis, returns that old C to the air as CO2.
During the Carboniferous Period around 350-400 million years ago, C burial exceeded weathering of C from rocks, and as a result O2 in air skyrocketed to up to ~30% by volume, compared with today's 21%. Too much C burial removed to much CO2 from air, leading to world cooling and the loss of rainforests worldwide. The C cycle can be perturbed, and the results can have a major impact on the biosphere.
Пікірлер: 6
Why were the oxygen levels so low 190 million years ago according to the chart @6:36?
@EarthParts
5 жыл бұрын
Oxygen levels were low during the Jurassic and Cretaceous Periods, and the reasons for this excursion aren't well understood. Likely options seem to include issues with ocean circulation leading to deep-sea anoxia, or the evolution of more plankton with organic-carbon shells instead of calcium carbonate shells might have altered the carbon cycle. Geochemical evidence (i.e. black shales laid down then) shows the low-O2 phase happened but there doesn't look to be a strong definitive consensus yet on what caused it.
Out of curiosity is this a hobby or do you teach a class with these?
@EarthParts
6 жыл бұрын
Yes, I teach an introductory geology course online at Western Michigan University, where I'm an associate professor in the Department of Geosciences. I'm building these videos to function as the lecture content for the course, so students taking the course get more out of it and have more to go on than just reading the textbook and taking exams on it. I take each topic from the syllabus and develop a video or set of videos to cover that subject in the same detail I'd provide in a traditional in-person class lecture series. I develop the storyboards for my videos directly from my own lecture slides & notes. My goal with Earth.Parts is to make all that content available for free to everyone, as basically a public service to promote better general understanding of the Earth & planetary sciences. Thanks for watching!
Random question. What will happen when Africa collided into Europe what will the mountain chain look like?
@EarthParts
6 жыл бұрын
Thanks for your question. Actually what you describe has happened a few times already; Africa and Europe are neighboring continents with an unquiet boundary and sometimes tectonic forces have pushed them together more aggressively than other times. The Alps are one big result of those two continents pushing together, and the active volcanoes of Italy are another dramatic expression of this massive tectonic event. I talk about this a lot in EarthParts #20, which focuses on continental collisions!