Does islam require burial of the dead?

Question

Does islam require burial of the dead? What verses/hadiths mandate that?

Can grave sites be reused after some time (e.g. 200 years) ? I am asking this because the practice of burying the dead in dedicated 25 sq ft of space, with the growing world population, yet ever more scarce arable land, seems like a wasteful practice, to say the least.

Answer 1

(1) Yes Islam requires a burial, It's fardh kifayath. What we get in quran is mentioned by Shoaib above. And there are hadiths saying to do the burial as early as possible :
روى البخاري ومسلم أن النبي صلى الله عليه وسلم قال: أسرعوا بالجنازة، فإن تك صالحة فخير تقدمونها عليه، وإن يكن سوى ذلك فشر تضعونه عن رقابكم. وقال صلى الله عليه وسلم: إذا مات أحدكم فلا تحبسوه، وأسرعوا به إلى قبره. قال الحافظ ابن حجر في فتح الباري: أخرجه الطبراني بإسناد حسن
Also there is an ijma'a of scholars that the burial is compulsory :
قال ابن المنذر في الإجماع: وأجمعوا على أن دفن الميت لازم، واجب على الناس، لا يسعهم تركه عند الإمكان، ومن قام به منهم سقط فرض ذلك على سائر المسلمين. اهــ. وهو من فروض الكفايات، بمعنى أنه لا يطلب من واحد من المسلمين بعينه أن يتولى دفنه، وإنما يجب أن يتولى بعضهم دفنه، فإن قام بعضهم بدفنه سقط الواجب عنهم جميعا، وإن لم يتول أحد دفنه أثموا جميعا
Says that the burial is compulsory, if someone from a community does that the all other muslims are freed.

(2) Yes Grave sites can be reused after a specific time This time changes with the location, the experts know the duration needed for the body to fully mixed with the soil.
Here are some words from scholars :
قال النووي الشافعي في المجموع: يجوز نبش القبر إذا بلي الميت وصار تراباً وحينئذ يجوز دفن غيره فيه، ويجوز زرع تلك الأرض وبناؤها وسائر وجوه الانتفاع والتصرف فيها باتفاق الأصحاب، وإن كانت عارية رجع فيها المعير، وهذا كله إذا لم يبق للميت أثر من عظم ولا غيره، قال أصحابنا رحمهم الله: ويختلف ذلك باختلاف البلاد والأرض ويعتمد فيه قول أهل الخبرة بها... إلى أن قال: وهذا كله إذا لم يبق للميت أثر من عظم وغيره، إلا أنه إذا دعت ضرورة لإدخال ميت على آخر قبل بلاء الأول جاز

You can see more here

Answer 2

There is the story, in Quran, of a man who kills his brother

Thereupon Allah sent forth a raven who began to scratch the earth to show him how he might cover the corpse of his brother. So seeing he cried: 'Woe unto me! Was I unable even to be like this raven and find a way to cover the corpse of my brother? Then he became full of remorse at his doing. (5:31)

This verse is self-explanatory as regards the preferred mode of disposing off the dead. Anthropologists would say that burial is a cultural artifact, but for a Muslim reading the Quran, that custom began with the guidance of God.

To answer your question about reusing graves, I think the following Hadith sufficiently covers it:

The Prophet (ﷺ) buried every two martyrs of Uhud in one grave. bukhari/23/101

Erecting tombs is not mandated by Islam, in fact it is abhorred. Possibly the best example of a truly Islamic graveyard is Jannat-Al-Baqih. However, in practice, the choice of decorating graves is somewhat directly proportional to the Sufic bent of the culture. The more the Sufi element in Muslim culture the more the tendency to decorate graves. This is perhaps due to the Sufi veneration of saints and Awlia-Allah posthumously by building shrines around their graves.