The core has the largest density, being made of iron and nickel
The mantle has an intermediate density and the crust has the lowest density.
The correct answer is - cyanobacteria.
The atmospheric oxygen came from the cyanobacteria. These were one of the earliest living organisms on Earth. The cyanobacteria was using photosynthesis in order to create its own food. The photosynthesis process requires sunlight, carbon dioxide, water, and oxygen. The oxygen is mostly released as a waste product from the process of photosynthesis, thus the cyanobacteria were literally releasing oxygen that was ending up into the atmosphere. As more and more cyanobacteria there were across the planet, more and more oxygen they were releasing into the atmosphere, slowly changing the composition of the atmosphere, and setting the basis of it as we know it now.
They were seeking greater economic opportunity, while some, such as the pilgrims in 1600s looking for freedom.
NOAA's Office for Coastal Management maintains a detailed online interactive mapping tool called Historical Hurricane Tracks at www.coast.noaa.gov/hurricanes. This tool offers users the ability to search and display global tropical cyclone data. The information can also be downloaded in widely-used GIS data formats.
Satellites, reconnaissance aircraft, Ships, buoys, radar, and other land-based platforms are important tools used in hurricane tracking and prediction. While a tropical cyclone is over the open ocean, remote measurements of the storm's intensity and track are made primarily via satellites.
