The reason scientists believe this is that there was basically no oxygen in the atmosphere at this time, which meant that cells needed to be anaerobic to survive,<span> going around the problem of no oxygen in the atmosphere.
Hope this helps.</span>
Answer:
<h3>The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in the Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo.</h3>
The right option here is the second choice listed - humans have
miscroscopic subunits in the kidneys called nephrons to filter blood,
and spiders have malpighian tubules to absorb salts and wastes.
