Default value for "created_at"

[aboutsam]

[Illuminate\Database\QueryException]
SQLSTATE[42000]: Syntax error or access violation: 1067 Invalid default value for 'created_at' (
SQL: create table comments (id int unsigned not null auto_increment primary key, text varc
har(255) not null, author varchar(255) not null, created_at timestamp default 0 not null, u pdated_at timestamp default 0 not null) default character set utf8 collate utf8_unicode_ci)