Sahih Al-Bukhari records that when Ibn `Abbas was question about this matter, he said that the earth was created before heaven, and the earth was spread out only after the creation of the heaven. Several Tafsir scholars of old and recent times also said similarly, as we have elaborated on in the Tafsir of Surat An-Nazi`at (chapter 79). The result of that discussion is that the word Daha (translated above as "spread'') is mentioned and explained in Allah's statement,
﴿وَالاٌّرْضَ بَعْدَ ذَلِكَ دَحَـهَا - أَخْرَجَ مِنْهَا مَآءَهَا وَمَرْعَـهَا - وَالْجِبَالَ أَرْسَـهَا ﴾
(And the earth, after that, He spread it out. And brought forth therefrom its water and its pasture. And the mountains He has fixed firmly.) (79:30-32)
Therefore, Daha means that the earth's treasures were brought to its surface after finishing the job of creating whatever will reside on earth and heaven. When the earth became Daha, the water burst out to its surface and the various types, colors, shapes and kinds of plants grew. The stars started rotating along with the planets that rotate around them. And Allah knows best.
﴿وَإِذْ قَالَ رَبُّكَ لِلْمَلَـئِكَةِ إِنِّي جَاعِلٌ فِى الأَرْضِ خَلِيفَةً قَالُواْ أَتَجْعَلُ فِيهَا مَن يُفْسِدُ فِيهَا وَيَسْفِكُ الدِّمَآءَ وَنَحْنُ نُسَبِّحُ بِحَمْدِكَ وَنُقَدِّسُ لَكَ قَالَ إِنِّي أَعْلَمُ مَا لاَ تَعْلَمُونَ ﴾
(30. And (remember) when your Lord said to the angels: "Verily, I am going to place (mankind) generations after generations on earth.'' They said: "Will You place therein those who will make mischief therein and shed blood, ـ while we glorify You with praises and thanks and sanctify You.'' He (Allah) said: "I know that which you do not know.'')