Bhashya
पृथिवी वाव गौतमाग्निरित्यादि पूर्ववत् ।तस्याः पृथि-व्याख्यस्याग्नेः संवत्सर एव समित्, संवत्सरेण हि कालेनसमिद्धा पृथिवी व्रीह्यादिनिष्पत्तये भवति ।आकाशो धूमः,पृथिव्या इवोत्थित आकाशो दृश्यते— यथा अग्नेर्धूमः ।रात्रिरर्चिः, पृथिव्या हि अप्रकाशात्मिकाया अनुरूपा रात्रिः,तमोरूपत्वात्—अग्नेरिवानुरूपमर्चिः ।दिशः अङ्गाराः, उप-शान्तत्वसामान्यात् ।अवान्तरदिशः विस्फुलिङ्गाः, क्षुद्र-त्वसामान्यात् ॥
In plain words
The earth itself is this fire, as explained before. For this earth-fire, the year is the fuel; through the passage of time the earth grows fruitful and brings forth grains. Space is its smoke, appearing to rise from the earth just as smoke rises from a hearth. Night is its flame, matching the dark nature of the earth just as a flame matches a fire. The directions are its embers, because of their quiet stillness, and the intermediate directions are its sparks, because of their smallness.
Close to the Sanskrit
The earth indeed is this fire of Gautama, as before. Of that fire named earth, the year alone is the fuel, for with time as fuel the earth becomes kindled for the production of rice and grains. Space is smoke; space is seen risen from the earth like smoke from fire. Night is the flame; night corresponds to the earth which is of a non-luminous nature, because of being of the nature of darkness—like the matching flame of a fire. The directions are the embers, due to the commonality of being tranquil. The intermediate directions are the sparks, due to the commonality of being small.