Sentences with phrase «widespread glaciation»

[65] Earlier still, a 200 - million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 Ma, by a colossal volcanic outgassing that raised the CO2 concentration of the atmosphere abruptly to 12 %, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day.

During the Oligocene (t = 38 to 22 m.y. ago), widespread glaciation probably occurred throughout Antarctica, although no ice cap existed.

Robock, A., C. M. Ammann, L. Oman, D. Shindell, S. Levis, and G. Stenchikov 2009: Did the Toba volcanic eruption of ~ 74k BP produce widespread glaciation?

On the other hand, during those periods between widespread glaciation, the water had melted from the ice sheets and polar areas, flowed, back into the oceans and sea level was as high or higher than now.

[10] Earlier still, a 200 - million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 million years ago, by a colossal volcanic outgassing which raised the CO2 concentration of the atmosphere abruptly to 12 percent, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day.

Climate models suggest that widespread glaciations couldn't take place at that time unless CO2 levels dropped to about eight times what they are at present, says Tim Lenton, an earth scientist at the University of Exeter in the United Kingdom.

Geologists knew of some fairly widespread glaciations in the past: there was an ice - age at the end of the Ordovician period, some 445 million years back and, going further back again, there were some huge, perhaps planet - wide glaciations in the Proterozoic eon.

Geologists knew of some fairly widespread glaciations in the past: there was an ice - age at the end of the Ordovician period, some 445 million years back and, going further back again, there were some huge, perhaps planet - wide glaciations in the Proterozoic eon.

Not exact matches

This Wisconsin glaciation left widespread impacts on the North American landscape.

The glaciological community has for decades harbored the widespread belief that the thermal evolution of the ice sheet, and the effect of this evolution on ice flow, are central in the ice - age cycling (not all communities agree, but there is plenty of literature on this from the land - ice crowd), so use of a temperature - independent rheology for the ice leaves out one favored explanation for termination of extensive glaciation.

Widespread indeed is the notion that very high CO2 in geologic past coincided with glaciation and that somehow negates today's relatively paltry 370 ppm CO2.

The three lines are: (1) the beginning: the Khirthar transgression and the onset of neritic carbonate accumulation in the Bartonian Age (preceding onset of the Middle Eocene climatic optimum [MECO]-RRB-; (2) the midlife change (Bartonian - Priabonian transition): the shift from carbonate - rich to carbonate - poor, higher - nutrient environments under estuarine circulation, causing widespread dysaerobia culminating in opaline silicas; and (3) the Eocene - Oligocene = Priabonian - Rupelian boundary and glaciation during oxygen isotope event Oi - 1, with return of improved ventilation in neritic environments and resumption of carbonate accumulation.

A CO2 threshold of below ~ 500 ppm is suggested for the initiation of widespread, continental glaciations, although this threshold was likely higher during the Paleozoic due to a lower solar luminosity at that time.

Does this mean that we are in for «widespread, continental glaciations»?

Although there is limited evidence of ice - rafted debris in the Arctic from the Miocene and into the Eocene, suggesting some continental glaciation (Stickley et al., 2009; St. John and Krissek, 2002), empirical evidence suggests that widespread Northern Hemisphere glaciation did not occur until 2.75 Ma (Ravelo et al., 2004), which is substantiated by recent Pliocene paleotemperature SST estimates near Svalbard between 10 and 18 °C (Robinson, 2009).

This is corroborated by model simulations indicating that atmospheric CO2 levels must fall below 280 ppmv to promote widespread continental glaciation of the Northern Hemisphere (DeConto et al., 2008) and 250 ppmv to promote major continental glaciation on Greenland (Lunt et al., 2008), both of which are well below recent estimates of Pliocene atmospheric CO2 estimates of ∼ 390 ppmv (Pagani et al., 2010).