Without these extreme greenhouse conditions, liquid water would not have occurred on the Earth’s surface.In contrast, direct evidence of rainfall in the geological record is very difficult to find.This enabled the atmospheric oxygen level to increase appreciably.By the time of the widespread appearance of eukaryotes at 1.8 billion years ago, oxygen concentration had risen to 10 percent of present atmospheric level (PAL).Glacial deposits are not necessarily limited to high latitudes.In general, they are complementary to the , and red beds that are climatically sensitive and restricted to low latitudes.It can also be inferred that stromatolite-bearing dolomites of rock, a sedimentary sequence spanning the period from 1.65 billion to 800 million years ago, were deposited in warm, tropical waters.
However, the presence of many types of filamentous microfossils dated to 3.45 billion years ago in the ) in BIFs.
The oxygen that combined the ferrous iron was provided as a waste product of cyanobacterial metabolism.
A major burst in the deposition of BIFs from 3.1 billion to 2.5 billion years ago—peaking about 2.7 billion years ago—cleared the oceans of ferrous iron.
Nevertheless, the original terminology to distinguish Precambrian rocks from all younger rocks is still used for subdividing within 50 degrees.
Most fossil carbonates, evaporites, phosphorites, and red beds of Phanerozoic age dating back to the Cambrian have a similar bimodal distribution with respect to their paleoequators.