Earth's first atmosphere was composed of mainly which of the following gases? O hydrogen and helium
O carbon dioxide and oxygen
O nitrogen and oxygen
O carbon monoxide and ozone

explanation:

since the crust is readily accessible, scientists have been able to perform hands-on experiments to determine its composition; studies on the more distant mantle and core have limited opportunities samples. so scientists also rely on analyses of seismic waves and gravity and as well as magnetic studies.

in plessy v. ferguson in 1896, the u.s. supreme court ruled that racially separate facilities, if equal, did not violate the constitution. segregation, the court said, wasn't discrimination.

in brown v. board of education, the court overturned plessy v. ferguson, and declared that racial segregation in public schools violated the equal protection clause of the 14th amendment.