Reverse chronology of post listing

I”m working on modifying a theme that is based on 2010.

I want to make the posts on this blog display earliest to oldest, but I don’t see how to do this in the theme:

I understand I need to add . "&order=ASC" to a wp_get_posts query, but I can’t find any.

Just index.php:
get_template_part( 'loop', 'index' );

and loop.php it seems to have the posts already:
while ( have_posts() ) : the_post();

Where should I look?

You can add code below to the beginning of loop.php

add_action('pre_get_posts', 'wpse_change_post_order');

function wpse_change_post_order($query){
    $query->set('order','ASC');
    $query->set('orderby','date');

}

the oldest posts will be in the home page.