Grit: how to to tell between two commits which is newer?

I'd like to be able to tell between two Grit::Commit objects, which is newer. What I mean by newer is that if commit_A is a parent (or parent of a parent,etc) of commit_B, then commit_B is newer. This assumes that commit_A and commit_B are on the same branch.

I thought about using Grit::Commit#date(), but I think this'll be inaccurate.

Any ideas?

Here is what I ended up implementing. See comments for explanation.

Performance is dog slow, but it was worse when using repo.git.rev_list(via method_missing).

require 'grit'

module Grit

    class Commit

        # Returns true if any commits in +commits+ are decendants of calling commit. True
        # means that one or more commits in +commits+ are newer.
        def has_decendant_in? *commits 
            total_commits = commits.flatten
            raise ArgumentError "at least one commit required." if total_commits.empty?
            total_commits.each do |commit|
                return true if repo.commits_between(commit.id, id).empty?
            end
            return false
        end

        # Returns an Array of commits which tie for being the newest commits. Ties can
        # occur when commits are in different branches.
        def self.newest *commits
            oldest_commits = []
            total_commits = commits.flatten
            raise ArgumentError "at least one commit required." if total_commits.empty?
            (total_commits).each do |commit|
                if commit.has_decendant_in?(total_commits - [commit])
                    oldest_commits << commit 
                end
            end
            return total_commits - oldest_commits
        end

    end

end