{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}


Indicang persistence also carbonate deposits predicted

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: [email protected] in [email protected] divergences –  In fact, later studies based on many more genes and many more lineages have reduced the discrepancy –  [email protected] animal age at ~700 mya •  Animals existed but were @ny or soe and lee no fossils –  Snowball Earth Snowball Earth •  Models 1960’s: Lowering of greenhouse gases  ­> cooling  ­> glacial ice and snow reflect heat ­ ­> [email protected] feedback for temperature drop •  Albedo = [email protected] of incoming [email protected] reflected back, increases with more ice •  Self ­reversing: Escape from the snowball through CO2 effect (J Kirschvink 1992) •  Evidence: synchronous glacial deposits globally, at or near equator, through reversals of [email protected] fields ([email protected] persistence) –  Also carbonate deposits predicted in the greenhouse sequel to the Snowball Earth have been found at many sites, capping the glacial deposits –  Many other [email protected] now being tested and extended –  Snowball Earth view is increasingly accepted •  [email protected] for Life on Earth? •  One of the hypothesized Snowball stages was about 550 Mya, beginning of Cambrian 6 4/9/13 Science 2004 Vernanimalcula - “Small spring animal” (after the ‘winter’ of Snowball Earth) ~ 180 microns long = 580-600 Mya Implies Bilateria arose well before Cam...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online