What is Palaeoproterozoic?
[[Image:Stromatolites Cochabamba.jpg|thumb|right|250px| Palaeoproterozoic [[stromatolite]] from [[Bolivia]], South America]] The '''Palaeoproterozoic''' was the first [[era]] of the [[Proterozoic]] [[eon]]. It came after the [[Archaean]] eon, and lasted from 2500 to 1600 [[million]] years ago (mya). In the Palaeoproterozoic, there was a huge production of [[stromatolite]]s by [[cyanobacteria]]. The first [[unicellular]] [[eukaryote]] organisms also appeared in the [[fossil]] record. The first [[supercontinent]] grew, and some of the rocks were normal [[sedimentary rock]]s, not [[Metamorphic rock|metamorphosed]]. == Basic differences in Earth physics == Because the Earth was only half as old as now, there were some basic differences from today. Heat in the Earth's interior was greater than today. This was mainly due to the higher abundance of [[radioactive]] [[isotope]]s, which decay as time passes. Temperatures at the surface were also higher, due to radiation from the Earth's interior, and due to a [[methane]] and [[carbon dioxide]]-based [[Greenhouse effect|greenhouse]] atmosphere. During the previous eon, the Archaean, the oceans were hot (55–85&nbsp;°C).<ref name=Reddy/> This was only partly balanced by the fact that the Sun's radiation was lower at that time. Paleontological evidence on the Earth's rotational history suggests that ~1.8 billion years ago, there were about 450 days in a year, implying 20 hour days.<ref>Giorgio Pannella 1972. [http://www.springerlink.com/content/u4pl7170jr5427t6/ Paleontological evidence on the Earth's rotational history since early precambrian] {{Webarchive|url=https://web.archive.org/web/20200706171244/http://www.springerlink.com/content/u4pl7170jr5427t6/ |date=2020-07-06 }} ''Astrophysics and Space Science'' '''16'''.2 p212</ref> Further back, the Earth day had about 17 hours, and there were 514±33 days per year. The Earth–Moon distance for the earliest Palaeoproterozoic was 51.9±3.3 Earth [[Radius|radii]] (compared to 60.27 at present).<ref>Williams G.E. 2000. Geologi