Hadean & Archean

3. the North and South Poles that align generally with the axis of rotation
5. Ultramafic lava from the Archean Eon
8. about 4.5 to 3.8 billion years ago, failed planets and smaller asteroids slammed into larger worlds
9. named for the underworld of the dead
11. a calcareous mound built up of layers of lime-secreting cyanobacteria and trapped sediment, found in Precambrian rocks as the earliest known fossils, and still being formed in lagoons in Australasia
17. any of the world's main continuous expanses of land
18. from red, orange and yellow to brilliant shades of green these form an organic crust on rocks and boulders
19. Αρχή (ancient Greek) for ‘Beginning’
20. oldest rock that is also metamorphic

1. mineral used to determine the age of very old rock
2. moon rock
4. the massive driving force that grinds solid rock into powder
6. Earth and Moon tug-of-war
7. also called lithospheric plate
10. large, dark, basaltic plains on Earth's Moon
12. Heavier elements spiraled and gelled together into planets of their own. Earth and the other terrestrial planets coalesced to form spheres. The heaviest material like zinc and iron sank to form an inner core. Finally, lighter material remained on top meshing together to create a crust.
13. In this time, the Earth's crust had cooled enough for continents to form and for the earliest known life to start
14. ancient planet in the early Solar System that, according to the giant-impact hypothesis, collided with the early Earth
15. 1 Billion Years
16. a large stable block of the earth's crust forming the nucleus of a continent