Most of the world's iron ore, including that found in northern Minnesota, formed during the middle Precambrian period, ranging in age from 1.8 to 2.5 billion years old. They are composed of alternating layers of iron-rich material, most often magnetite or
hematite, and silica. These iron oxide minerals formed on the ocean floor, creating the banded iron deposits you see here. What
was the source of the oxygen that helped to produce these deposits?
A)
B)
The oxygen that was released into the atmosphere as a by-product of
photosynthesis caused iron deposits to oxidize creating the iron oxide
minerals
Photosynthetic organisms making oxygen as a by-product of
photosynthesis and the oxygen reacted with the iron dissolved in seawater
to form iron oxide minerals.
The decomposition of carbon-based life forms in the oceans released
oxygen and carbon dioxide. These gases reacted with the iron deposits
forming the minerals mentioned
in Earths early biosphere there were not organisms that underwent
aerobic cellular respiration and an excess oxygen built up in the
atmosphere. This oxygen reacted with iron deposits to form iron oxide
minerals
D

The speed of  sound:   sound travels  at different speeds depending on what it istraveling through. of the three mediums (gas, liquid, and solid)  sound waves travel the slowest through  gases, faster  through  liquids, and fastest  through  solids.

Nitrate poisoning for the first onebaby blue syndrome

Mantle convection  is the slow  creepingmotion of earth's solid silicate  mantle  caused by  convection  currents carrying  heat from the interior  to the planet's surface.[1][2]  the earth's surface  lithosphere, which rides atop the  asthenosphere  (the two components of the  upper mantle), is divided into a number of  plates  that are continuously being created and consumed at their opposite  plate boundaries. accretion occurs as mantle is added to the growing edges of a plate, associated with  seafloor spreading. this hot added material cools down by  conduction  and  convection  of heat. at the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of  subduction  usually at an  ocean trench.[3]this subducted material sinks through the earth's interior. some subducted material appears to reach the lower mantle,[4]  while in other regions, this material is impeded from sinking further, possibly due to a phase transition from  spinel  to  silicate perovskiteand  magnesiowustite, an  endothermic reaction.[5]the subducted oceanic crust triggers  volcanism, although the basic mechanisms are varied. volcanism may occur due to processes that add buoyancy to partially melted mantle causing an upward flow due to a decrease in density of the partial melt.secondary forms of convection that may result in surface volcanism are postulated to occur as a consequence of intraplate extension[6]  and  mantle plumes.[7]it is because the mantle can convect that the  tectonic plates  are able to move around the earth's surface.[8]mantle convection seems to have been much more active during the  hadean  period, resulting in gravitational sorting of heavier molten  iron, and  nickel  elements and  sulphides  in the core, and lighter  silicate minerals  in the  mantle.