Final answer:
The main reasons Earth lacked a substantial atmosphere during accretion and early heating include not enough gravitational attraction, high temperatures preventing retention of gases, and the absence of a differentiated core to produce a protective magnetic field. Over time, Earth cooled, volcanic activity increased, and impacts from space contributed to the formation of an early atmosphere and oceans.
Step-by-step explanation:
The main answer to why Earth probably did not have much of an atmosphere during the period of accretion and early heating is 4) all of the above. Initially, Earth would not have been dense enough to have enough gravitational attraction to retain the light gases that make up an atmosphere. Moreover, the high heat from accretion and core formation would prevent Earth from retaining volatile compounds like gases, as they would escape into space. Additionally, a differentiated core, which generates a magnetic field to shield and protect an atmosphere from solar winds, would not yet have existed.Early heating of the Earth would have contributed to the loss of atmosphere due to the thermal escape of gases. And without a magnetic field, the solar winds would strip away particles from the upper atmosphere. Over time, as the Earth continued to cool and volcanism increased, gases such as water vapor, carbon dioxide, methane, and ammonia released from the planet's interior started to accumulate, forming the early atmosphere. This was further enriched by impacts from comets and asteroids, leading to the atmosphere and oceans we have today.In conclusion, the combination of insufficient gravity, high temperatures, and lack of a protective magnetic field contributed to Earth's initial inability to maintain a substantial atmosphere during the accretion phase and early heating periods.