Precambrian Earth

3. molecules that combine to form proteins
7. a microscopic single-celled organism that has neither a distinct nucleus with a membrane nor other specialized organelles. Prokaryotes include the bacteria and cyanobacteria.
9. a sedimentary deposit that consists of alternating thin layers of iron oxides (such as magnetite or hematite) and iron-poor minerals (such as shale or chert)
10. a laminated usually mounded sedimentary fossil formed from layers of cyanobacteria, calcium carbonate, and trapped sediment
11. sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides.
13. a land mass that was an independent continent about 500 million years ago and that currently includes Greenland and a large part of the North American continent
14. any cell or organism that possesses a clearly defined nucleus.
15. a small rocky body orbiting the sun. Large numbers of these, ranging in size from nearly 600 miles (1,000 km) across (Ceres) to dust particles, are found (as the asteroid belt ) especially between the orbits of Mars and Jupiter, though some have more eccentric orbits, and a few pass close to the earth or enter the atmosphere as meteors.
17. the nuclear area of Precambrian rocks present in each of the continents.

1. When planets begin to melt, the materials in them begin to separate from one another. The heaviest materials, such as metallic iron, sink to form cores. Low-density magmas rise, forming crusts.
2. any of a major group (Cyanobacteria) of photosynthetic bacteria that are single-celled but often form colonies in the form of filaments, sheets, or spheres and are found in diverse environments (such as salt and fresh water, soils, and on rocks)
4. an isolated fragment of continental crust forming part of a small crust plate.
5. a meteor that survives its passage through the earth's atmosphere such that part of it strikes the ground. More than 90 percent of meteorites are of rock, while the remainder consist wholly or partly of iron and nickel.
6. a large stable block of the earth's crust forming the nucleus of a continent.
8. one of the world's largest geologic continental shields, centered on Hudson Bay and extending for 8 million square km
12. taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period
16. a mineral occurring as prismatic crystals, typically brown but sometimes in translucent varieties of gem quality. It consists of zirconium silicate and is the chief ore of zirconium.