The greenhouse effect and ozone hole issues are, however, related. For example, CFCs are involved in both issues: CFCs, in addition to destroying stratosphere ozone, are also greenhouse gases. It has traditionally been thought there is not much mixing of the troposphere and stratosphere. But there is recent evidence of transport of stratospheric ozone into the troposphere (see "Ozone-rich transients in the upper equatorial Atlantic troposphere," by Suhre et al., Nature , Vol. 388, 14 August 1997, pages 661-663, and the related discussion paper, "Ozone clouds over the Atlantic," by Crutzen and Lawrence, on pages 625-626 in the same issue of Nature ). So ozone depletion in the stratosphere could result in reduced concentrations of this greenhouse gas in the troposphere. Conversely, global climate change could also affect ozone depletion through changes in stratospheric temperature and water vapor (see "The effect of climate change on ozone depletion through changes in stratospheric water vapour," by Kirk-Davidoff et al., Nature, Vol. 402, 25 November 1999, pages 399-401).
The increased carbon dioxide amount in the atmosphere that causes global warming is a cause of concern for many people because of its potential dangerous effects to the Earth and the environment....
This analysis and discussion activity introduces students to the basic principles of how biological organisms use energy. The focus is on understanding the roles of ATP and cellular respiration. In addition, students apply the principles of conservation of energy and conservation of matter to avoid common errors and correct common misconceptions. (NGSS)
These Teacher Notes summarize basic concepts and information related to energy, ATP, cellular respiration, and photosynthesis. These Teacher Notes also review common misconceptions and suggest a sequence of learning activities designed to develop student understanding of important concepts and overcome any misconceptions.
There are many solutions to slowing or stopping the effects of global warming including planting trees, cutting carbon dioxide emissions, and using alternative fuels....
In Paleocene oceans, sharks filled the empty niches left by aquatic reptiles, but it took coral reefs ten million years to begin to recover, . As Africa and India moved northward, the shrank, and in the late Paleocene and early Eocene, one of the last Tethyan anoxic events laid down Middle East oil, and the last Paleocene climate event is called the (“PETM”). The PETM has been the focus of a great deal of recent research because of its parallels to today’s industrial era, when carbon dioxide and other greenhouse gases are massively vented to the atmosphere, causing a warming atmosphere and acidifying oceans. The seafloor communities suffered a mass extinction and the PETM’s causes are uncertain, but the when the global ocean warmed sufficiently is a prominent hypothesis. Scientists also look to the usual suspects of volcanism, changes in oceanic circulation, and a bolide impact.
When sea levels rise as dramatically as they did in the Cretaceous, coral reefs will be buried under rising waters and the ideal position, for both photosynthesis and oxygenation, is lost, and reefs can die, like burying a tree’s roots. About 125 mya, reefs made by , which thrived on , began to displace reefs made by stony corals. They may have prevailed because they could tolerate hot and saline waters better than stony corals could. About 116 mya, an , probably caused by volcanism, which temporarily halted rudist domination. But rudists flourished until the late Cretaceous, when they went extinct, perhaps due to changing climate, although there is also evidence that the rudists . Carbon dioxide levels steadily fell from the early Cretaceous until today, temperatures fell during the Cretaceous, and hot-climate organisms gradually became extinct during the Cretaceous. Around 93 mya, , perhaps caused by underwater volcanism, which again seems to have largely been confined to marine biomes. It was much more devastating than the previous one, and rudists were hit hard, although it was a more regional event. That event seems to have , and a family of . On land, , some of which seem to have , also went extinct. There had been a decline in sauropod and ornithischian diversity before that 93 mya extinction, but it subsequently rebounded. In the oceans, biomes beyond 60 degrees latitude were barely impacted, while those closer to the equator were devastated, which suggests that oceanic cooling was related. shows rising oxygen and declining carbon dioxide in the late Cretaceous, which reflected a general cooling trend that began in the mid-Cretaceous. Among the numerous hypotheses posited, late Cretaceous climate changes have been invoked for slowly driving dinosaurs to extinction, in the “they went out with a whimper, not a bang” scenario. However, it seems that dinosaurs did go out with a bang. A big one. Ammonoids seem to have been brought to the brink with nearly marine mass extinctions during their tenure on Earth, and it was no different with that late-Cretaceous extinction. Ammonoids recovered once again, and their lived in the late Cretaceous, but the end-Cretaceous extinction marked their final appearance as they went the way of and other iconic animals.
It can be helpful at this juncture to grasp the cumulative impact of , inventing , inventing , inventing that made possible, and inventing . Pound-for-pound, the complex organisms that began to dominate Earth’s ecosphere during the Cambrian Period consumed energy about 100,000 times as fast as the Sun produced it. Life on Earth is an incredibly energy-intensive phenomenon, powered by sunlight. In the end, only so much sunlight reaches Earth, and it has always been life’s primary limiting variable. Photosynthesis became more efficient, aerobic respiration was an order-of-magnitude leap in energy efficiency, the oxygenation of the atmosphere and oceans allowed animals to colonize land and ocean sediments and even fly, and life’s colonization of land allowed for a . Life could exploit new niches and even help create them, but the key innovations and pioneering were achieved long ago. If humanity attains the , new niches will arise, even of the , but all other creatures living on Earth have constraints, primarily energy constraints, which produce very real limits. Life on Earth has largely been a for several hundred million years, but the Cambrian Explosion was one of those halcyonic times when animal life had its greatest expansion, not built on the bones of a mass extinction so much as blazing new trails.
Before the era of mass extinction investigation that began in the 1980s, a hundred hypotheses were presented in the scientific literature for the dinosaur extinction, but it was a kind of scientific parlor game. Scientists from all manner of specialties concocted their hypotheses. But even during the current era of scientific study of mass extinctions, much is unknown or controversial and even the data is in dispute, let alone its interpretation. Dynamics may have conflated to produce catastrophic effects, such as increasing atmospheric carbon dioxide concentration warming the land and oceans to the extent that otherwise stable on the ocean floor and in permafrost would be liberated and escape into the atmosphere. That situation is to the , , and extinctions, as well as helping end the . Today, there is genuine fear among climate scientists that , as global warming continues and hydrocarbons are burned with abandon, which could contribute to catastrophic runaway conditions. Wise scientists admit that humanity is currently conducting a huge chemistry experiment with Earth, and while the outcomes are far from certain, the .
Mass extinctions always have critical geophysical aspects to them, and often geochemical. Continental shelves under shallow seas, which are home to most marine life, are vulnerable to sea level and oceanic current changes. Stagnant waters, or waters that have too many nutrients dumped into them, can lose their oxygen, which triggers anoxic events that kill complex life. A continental shelf exposed to the atmosphere by a falling sea level would obviously lose its marine life, and that marine life might have had nowhere else to go. Sea levels can rise or fall for different reasons. The most obvious reason has been advancing and retreating ice sheets, as water is removed from or added to the oceans, but the aggregate continental landmass has always grown (possibly sporadically), continents can rise and can fall during the journeys of their tectonic plates, and the ocean’s collective basin has fluctuated in size, as water was hydrated into rocks, and also falling when and rising again as they fragmented. Generally, when , the continental shelves lost their marine life, and , anoxic conditions often accompanied them. There is evidence that the ozone layer has been periodically damaged, which stressed all plants and animals that the Sun directly shined on. The positions of the continents, both in relation to each other and their proximity to the equator or poles, can have dramatic effects, including impacts on global climate. Global climate changes and moving continents can turn rainforests into deserts and vice versa.